A novel remediation strategy of mixed calcium peroxide and degrading bacteria for polycyclic aromatic hydrocarbon contaminated water

Polycyclic aromatic hydrocarbons (PAHs) are a class of toxic organic pollutants commonly detected in the aqueous phase. Traditional biodegradation is inefficient and advanced oxidation technologies are expensive. In the current study, a novel strategy was developed using calcium peroxide (CP) and PAH-degrading bacteria (PDB) to effectively augment PAH degradation by 28.62-59.22%. The PDB consisted of the genera Acinetobacter, Stenotrophomonas, and Comamonas. Applying the response surface model (RSM), the most appropriate parameters were identified, and the predictive degradation rates of phenanthrene (Phe), pyrene (Pyr), and ΣPAHs were 98%, 76%, and 84%, respectively. The constructed mixed system could reduce 90% of Phe and more than 60% of ΣPAHs and will perform better at pH 5-7 and lower salinity. Because PAHs tend to bind to dissolved organic matter (DOM) with larger molecular weights, humic acid (HA) had a larger negative effect on the PAH-degradation efficiency of the CP-PDB mixed system than fulvic acid (FA). The proposed PAH-degradation pathways in the mixed system were based on the detection of intermediates at different times. The investigation constructed and optimized a novel environmental PAH-degradation strategy. The synergistic application of PDB and oxidation was extended for organic contaminant degradation in aqueous environments.

In Situ Mitochondrial Biomineralization for Drug-Free Cancer Therapy

The common clinical chemotherapy often brings serious side effects to patients, mainly due to the off-target and leakage of toxic drugs. However, this is fatal for some specific clinical tumors, such as brain tumors and neuroma. This study performs a drug-free approach by encapsulating black phosphorus (BP) and calcium peroxide (CaO2) in liposomes with surface-modified triphenylphosphonium (BCLT) to develop mitochondria targeting calcification for cancer therapy without damaging normal cells. BCLT preferentially accumulates inside tumor mitochondria and then is activated by near-infrared (NIR) laser irradiation to produce abundant PO4 3- and Ca2+ to accelerate in situ mitochondrial mineralization, leading to mitochondrial dysfunction and cancer cell death. More importantly, both PO4 3- and Ca2+ are essential components of metabolism in the body, and random gradient diffusion or premature leakage does not cause damage to adjacent normal cells. This achievement promises to be an alternative to conventional chemotherapy in clinical practice for many specific tumor types.

Enzymatic machinery of wood-inhabiting fungi that degrade temperate tree species

Deadwood provides habitat for fungi and serves diverse ecological functions in forests. We already have profound knowledge of fungal assembly processes, physiological and enzymatic activities, and resulting physico-chemical changes during deadwood decay. However, in situ detection and identification methods, fungal origins, and a mechanistic understanding of the main lignocellulolytic enzymes are lacking. This study used metaproteomics to detect the main extracellular lignocellulolytic enzymes in 12 tree species in a temperate forest that have decomposed for 8 ½ years. Mainly white-rot (and few brown-rot) Basidiomycota were identified as the main wood decomposers, with Armillaria as the dominant genus; additionally, several soft-rot xylariaceous Ascomycota were identified. The key enzymes involved in lignocellulolysis included manganese peroxidase, peroxide-producing alcohol oxidases, laccase, diverse glycoside hydrolases (cellulase, glucosidase, xylanase), esterases, and lytic polysaccharide monooxygenases. The fungal community and enzyme composition differed among the 12 tree species. Ascomycota species were more prevalent in angiosperm logs than in gymnosperm logs. Regarding lignocellulolysis as a function, the extracellular enzyme toolbox acted simultaneously and was interrelated (e.g. peroxidases and peroxide-producing enzymes were strongly correlated), highly functionally redundant, and present in all logs. In summary, our in situ study provides comprehensive and detailed insight into the enzymatic machinery of wood-inhabiting fungi in temperate tree species. These findings will allow us to relate changes in environmental factors to lignocellulolysis as an ecosystem function in the future.

Enhancing cold and drought tolerance in cotton: a protective role of SikCOR413PM1

The present study explored the potential role of cold-regulated plasma membrane protein COR413PM1 isolated from Saussurea involucrata (Matsum. & Koidz)(SikCOR413PM1), in enhancing cotton (Gossypium hirsutum) tolerance to cold and drought stresses through transgenic methods. Under cold and drought stresses, the survival rate and the fresh and dry weights of the SikCOR413PM1-overexpressing lines were higher than those of the wild-type plants, and the degree of leaf withering was much lower. Besides, overexpressing SikCOR413PM1 overexpression increased the relative water content, reduced malondialdehyde content and relative conductivity, and elevated proline and soluble sugar levels in cotton seedlings. These findings suggest that SikCOR413PM1 minimizes cell membrane damage and boosts plant stability under challenging conditions. Additionally, overexpression of this gene upregulated antioxidant enzyme-related genes in cotton seedlings, resulting in enhanced antioxidant enzyme activity, lowered peroxide content, and reduced oxidative stress. SikCOR413PM1 overexpression also modulated the expression of stress-related genes (GhDREB1A, GhDREB1B, GhDREB1C, GhERF2, GhNAC3, and GhRD22). In field trials, the transgenic cotton plants overexpressing SikCOR413PM1 displayed high yields and increased environmental tolerance. Our study thus demonstrates the role of SikCOR413PM1 in regulating stress-related genes, osmotic adjustment factors, and peroxide content while preserving cell membrane stability and improving cold and drought tolerance in cotton.

New insights into peroxide toxicology: sporulenes help Bacillus subtilis endospores from hydrogen peroxide

AIM

The purpose of the present study was to understand the possible events involved in the toxicity of hydrogen peroxide (H2O2) to wild and sporulene-deficient spores of Bacillus subtilis, as H2O2 was previously shown to have deleterious effects.

METHODS AND RESULTS

The investigation utilized two strains of B. subtilis, namely the wild-type PY79 (WT) and the sporulene-deficient TB10 (ΔsqhC mutant). Following treatment with 0.05% H2O2 (v/v), spore viability was assessed using a plate count assay, which revealed a significant decrease in cultivability of 80% for the ΔsqhC mutant spores. Possible reasons for the loss of spore viability were investigated with microscopic analysis, dipicholinic acid (DPA) quantification and propidium iodide (PI) staining. Microscopic examinations revealed the presence of withered and deflated morphologies in spores of ΔsqhC mutants treated with H2O2, indicating a compromised membrane permeability. This was further substantiated by the absence of DPA and a high frequency (50%-75%) of PI infiltration. The results of fatty acid methyl ester analysis and protein profiling indicated that the potentiation of H2O2-induced cellular responses was manifested in the form of altered spore composition in ΔsqhC B. subtilis. The slowed growth rates of the ΔsqhC mutant and the heightened sporulene biosynthesis pathways in the WT strain, both upon exposure to H2O2, suggested a protective function for sporulenes in vegetative cells.

CONCLUSIONS

Sporulenes serve as a protective layer for the inner membrane of spores, thus assuming a significant role in mitigating the adverse effects of H2O2 in WT B. subtilis. The toxic effects of H2O2 were even more pronounced in the spores of the ΔsqhC mutant, which lacks this protective barrier of sporulenes.

Aquaporin-7 Facilitates Proliferation and Adipogenic Differentiation of Mouse Bone Marrow Mesenchymal Stem Cells by Regulating Hydrogen Peroxide Transport

Hydrogen peroxide (H2O2) is a major form of reactive oxygen species that play an important role in the survival, proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs). The regulatory mechanisms of H2O2 homeostasis in BMSCs are not fully understood. Here we demonstrate for the first time that aquaglyceroporin AQP7 is a functional peroxiporin expressed in BMSCs and remarkably upregulated upon adipodenic induction. The proliferation ability of BMSCs from AQP7-/- mice was significantly decreased, as indicated by fewer clonal formation and cell cycle arrest compared with wildtype BMSCs. AQP7 deficiency caused accumulation of intracellular generated H2O2 during BMSCs proliferation, leading to oxidative stress and inhibition of PI3K/AKT and STAT3 signaling pathways. After adipogenic induction, however, the AQP7-/- BMSCs exhibited greatly reduced adipogenic differentiation with fewer lipid droplets formation and lower cellular triglycerides content than wildtype BMSCs. In such case AQP7 deficiency was found to diminish import of extracellular H2O2 produced by plasma membrane NADPH Oxidases, resulting in altered AMPK and MAPK signaling pathways and reduced expression of lipogenic genes C/EBPα and PPARγ. Our data revealed a novel regulatory mechanism of BMSCs function through AQP7-mediated H2O2 transport across plasma membrane. AQP7 is a peroxiporin mediating H2O2 transport across the plasma membrane of BMSCs. During proliferation, AQP7 deficiency results in accumulation of intracellular generated H2O2 due to reduced export, which inhibited STAT3 and PI3K/AKT/insulin receptor signaling pathways and cell proliferation. During adipogenic differentiation, however, AQP7 deficiency blocked the uptake of extracelluar H2O2 generated through plasma membrane NOX enzymes. The reduced intracellular H2O2 level causes decreased expression of lipogenic genes C/EBPα and PPARγ due to altered AMPK and MAPK signaling pathways, leading to impaired adipogenic differentiation.

The multifaceted nature of peroxiredoxins in chemical biology

Peroxiredoxins (Prx), thiol-dependent peroxidases, were first identified as H2O2 detoxifiers, and more recently as H2O2 sensors, intermediates in redox-signaling pathways, metabolism modulators, and chaperones. The multifaceted nature of Prx is not only dependent on their peroxidase activity but also strongly associated with specific protein-protein interactions that are being identified, and where the Prx oligomerization dynamics plays a role. Their oxidation by a peroxide substrate forms a sulfenic acid that opens a route to channel the redox signal to diverse protein targets. Recent research underscores the importance of different Prx isoforms in the cellular processes behind disease development with potential therapeutic applications.

Molecular therapy of cardiac ischemia-reperfusion injury based on mitochondria and ferroptosis

Excessive death of myocardial cells can lead to various cardiovascular diseases and even develop into heart failure, so developing ideal treatment plans based on pathogenesis is of great significance for cardiopathy. After the heart undergoes ischemia‒reperfusion (I/R), myocardial cells accumulate a large amount of peroxides, leading to mitochondrial dysfunction and inducing ferroptosis. Ferroptosis is a form of iron-dependent regulatory cell death (RCD) caused by imbalanced redox and iron metabolism that leads to severe cell damage through the accumulation of peroxides. The mechanism of ferroptosis is highly correlated with mitochondrial metabolism. Myocardial cells are rich in a large number of mitochondria, which serve as energy supply centers and are prone to producing reactive oxygen species (ROS), providing opportunities for oxidative stress caused by ferroptosis. Ferroptosis is related to various cardiovascular diseases, and potential treatment methods designed around ferroptosis may alter the pathological progression of cardiovascular diseases. Therefore, this review investigates the regulatory mechanisms of ferroptosis, exploring the close pathological and physiological connections between ferroptosis and mitochondrial and cardiac I/R injury. Targeting ferroptosis and mitochondria for intervention may be an effective plan for preventing and treating cardiac I/R injury.

Imaging of mtHyPer7, a Ratiometric Biosensor for Mitochondrial Peroxide, in Living Yeast Cells

Mitochondrial dysfunction, or functional alteration, is found in many diseases and conditions, including neurodegenerative and musculoskeletal disorders, cancer, and normal aging. Here, an approach is described to assess mitochondrial function in living yeast cells at cellular and subcellular resolutions using a genetically encoded, minimally invasive, ratiometric biosensor. The biosensor, mitochondria-targeted HyPer7 (mtHyPer7), detects hydrogen peroxide (H2O2) in mitochondria. It consists of a mitochondrial signal sequence fused to a circularly permuted fluorescent protein and the H2O2-responsive domain of a bacterial OxyR protein. The biosensor is generated and integrated into the yeast genome using a CRISPR-Cas9 marker-free system, for more consistent expression compared to plasmid-borne constructs. mtHyPer7 is quantitatively targeted to mitochondria, has no detectable effect on yeast growth rate or mitochondrial morphology, and provides a quantitative readout for mitochondrial H2O2 under normal growth conditions and upon exposure to oxidative stress. This protocol explains how to optimize imaging conditions using a spinning-disk confocal microscope system and perform quantitative analysis using freely available software. These tools make it possible to collect rich spatiotemporal information on mitochondria both within cells and among cells in a population. Moreover, the workflow described here can be used to validate other biosensors.

Structural evidence for intermediates during O2 formation in photosystem II

In natural photosynthesis, the light-driven splitting of water into electrons, protons and molecular oxygen forms the first step of the solar-to-chemical energy conversion process. The reaction takes place in photosystem II, where the Mn4CaO5 cluster first stores four oxidizing equivalents, the S0 to S4 intermediate states in the Kok cycle, sequentially generated by photochemical charge separations in the reaction center and then catalyzes the O-O bond formation chemistry1-3. Here, we report room temperature snapshots by serial femtosecond X-ray crystallography to provide structural insights into the final reaction step of Kok's photosynthetic water oxidation cycle, the S3→[S4]→S0 transition where O2 is formed and Kok's water oxidation clock is reset. Our data reveal a complex sequence of events, which occur over micro- to milliseconds, comprising changes at the Mn4CaO5 cluster, its ligands and water pathways as well as controlled proton release through the hydrogen-bonding network of the Cl1 channel. Importantly, the extra O atom Ox, which was introduced as a bridging ligand between Ca and Mn1 during the S2→S3 transition4-6, disappears or relocates in parallel with Yz reduction starting at approximately 700 μs after the third flash. The onset of O2 evolution, as indicated by the shortening of the Mn1-Mn4 distance, occurs at around 1,200 μs, signifying the presence of a reduced intermediate, possibly a bound peroxide.

Protein S-glutathionylation and sex dimorphic effects on hydrogen peroxide production by dihydroorotate dehydrogenase in liver mitochondria

Dihydroorotate dehydrogenase (DHODH) oxidizes dihydroorotate to orotate for pyrimidine biosynthesis, donating electrons to the ubiquinone (UQ) pool of mitochondria. DHODH has a measurable rate for hydrogen peroxide (H₂O₂) production and thus contributes to cellular changes in redox tone. Protein S-glutathionylation serves as a negative feedback loop for the inhibition of H₂O₂ by several α-keto acid dehydrogenases and respiratory complexes in mitochondria, as well as ROS sources in liver cytoplasm. Here, we report this redox signaling mechanism also inhibits H₂O₂ production by DHODH in liver mitochondria isolated from male and female C57BL6N mice. We discovered that low amounts of the glutathionylation catalyst, disulfiram (50-500 nM), almost abolished H₂O₂ production by DHODH in mitochondria from male mice. Similar results were collected with diamide, however, higher doses (1000-5000 μM) were required to elicit this effect. Disulfiram and diamide also significantly suppressed H₂O₂ production by DHODH in female liver mitochondria. However, liver mitochondria from female mice were more resistant to disulfiram or diamide-mediated inhibition of H₂O₂ genesis when compared to samples from males. Analysis of the impact of disulfiram and diamide on DHODH activity revealed that both compounds inhibited the dehydrogenase directly, however the effect was less in female mice. Additionally, disulfiram and diamide impeded the use of dihydroorotate fueled oxidative phosphorylation in mitochondria from males and females, although samples collected from female rodents displayed more resistance to this inhibition. Taken together, our findings demonstrate H₂O₂ production by DHODH can be inhibited by glutathionylation and sex can impact this redox modification.

Metal binding and oligomerization properties of FurC (PerR) from Anabaena sp. PCC7120: an additional layer of regulation?

Metal and redox homeostasis in cyanobacteria is tightly controlled to preserve the photosynthetic machinery from mismetallation and minimize cell damage. This control is mainly taken by FUR (ferric uptake regulation) proteins. FurC works as the PerR (peroxide response) paralog in Anabaena sp. PCC7120. Despite its importance, this regulator remained poorly characterized. Although FurC lacks the typical CXXC motifs present in FUR proteins, it contains a tightly bound zinc per subunit. FurC:Zn stoichiometrically binds zinc and manganese in a second site, being manganese more efficient in the binding of FurC:Zn to its DNA target PprxA. Oligomerization analyses of FurC:Zn evidence the occurrence of different aggregates ranging from dimers to octamers. Notably, intermolecular disulfide bonds are not involved in FurC:Zn dimerization, being the dimer the most reduced form of the protein. Oligomerization of dimers occurs upon oxidation of thiols by H2O2 or diamide and can be reversed by DTT. Irreversible inactivation of the regulator occurs by metal catalyzed oxidation promoted by ferrous iron. However, inactivation upon oxidation with H2O2 in the absence of iron was reverted by addition of DTT. Comparison of models for FurC:Zn dimers and tetramers obtained using AlphaFold Colab and SWISS-MODEL allowed to infer the residues forming both metal-binding sites and to propose the involvement of Cys86 in reversible tetramer formation. Our results decipher the existence of two levels of inactivation of FurC:Zn of Anabaena sp. PCC7120, a reversible one through disulfide-formed FurC:Zn tetramers and the irreversible metal catalyzed oxidation. This additional reversible regulation may be specific of cyanobacteria.

Selenoprotein P - Selenium transport protein, enzyme and biomarker of selenium status

The habitual intake of selenium (Se) varies strongly around the world, and many people are at risk of inadequate supply and health risks from Se deficiency. Within the human organism, efficient transport mechanisms ensure that organs with a high demand and relevance for reproduction and survival are preferentially supplied. To this end, selenoprotein P (SELENOP) is synthesized in the liver and mediates Se transport to essential tissues such as the endocrine glands and the brain, where the "SELENOP cycle" maintains a privileged Se status. Mouse models indicate that SELENOP is not essential for life, as supplemental Se supply was capable of preventing the development of severe symptoms. However, knockout mice died under limiting supply, arguing for an essential role of SELENOP in Se deficiency. Many clinical studies support this notion, pointing to close links between health risks and low SELENOP levels. Accordingly, circulating SELENOP concentrations serve as a functional biomarker of Se supply, at least until a saturated status is achieved and SELENOP levels reach a plateau. Upon toxic intake, a further increase in SELENOP is observed, i.e., SELENOP provides information about possible selenosis. The SELENOP transcripts predict an insertion of ten selenocysteine residues. However, the decoding is imperfect, and not all these positions are ultimately occupied by selenocysteine. In addition to the selenocysteine residues near the C-terminus, one selenocysteine resides central within an enzyme-like environment. SELENOP proved capable of catalyzing peroxide degradation in vitro and protecting e.g. LDL particles from oxidation. An enzymatic activity in the intact organism is unclear, but an increasing number of clinical studies provides evidence for a direct involvement of SELENOP-dependent Se transport as an important and modifiable risk factor of disease. This interaction is particularly strong for cardiovascular and critical disease including COVID-19, cancer at various sites and autoimmune thyroiditis. This review briefly highlights the links between the growing knowledge of Se in health and disease over the last 50 years and the specific advances that have been made in our understanding of the physiological and clinical contribution of SELENOP to the current picture.

Ohr - OhrR, a neglected and highly efficient antioxidant system: Structure, catalysis, phylogeny, regulation, and physiological roles

Ohrs (organic hydroperoxide resistance proteins) are antioxidant enzymes that play central roles in the response of microorganisms to organic peroxides. Here, we describe recent advances in the structure, catalysis, phylogeny, regulation, and physiological roles of Ohr proteins and of its transcriptional regulator, OhrR, highlighting their unique features. Ohr is extremely efficient in reducing fatty acid peroxides and peroxynitrite, two oxidants relevant in host-pathogen interactions. The highly reactive Cys residue of Ohr, named peroxidatic Cys (C_p), composes together with an arginine and a glutamate the catalytic triad. The catalytic cycle of Ohrs involves a condensation between a sulfenic acid (C_p-SOH) and the thiol of the second conserved Cys, leading to the formation of an intra-subunit disulfide bond, which is then reduced by dihydrolipoamide or lipoylated proteins. A structural switch takes place during catalysis, with the opening and closure of the active site by the so-called Arg-loop. Ohr is part of the Ohr/OsmC super-family that also comprises OsmC and Ohr-like proteins. Members of the Ohr, OsmC and Ohr-like subgroups present low sequence similarities among themselves, but share a high structural conservation, presenting two Cys residues in their active site. The pattern of gene expression is also distinct among members of the Ohr/OsmC subfamilies. The expression of ohr genes increases upon organic hydroperoxides treatment, whereas the signals for the upregulation of osmC are entry into the stationary phase and/or osmotic stress. For many ohr genes, the upregulation by organic hydroperoxides is mediated by OhrR, a Cys-based transcriptional regulator that only binds to its target DNAs in its reduced state. Since Ohrs and OhrRs are involved in virulence of some microorganisms and are absent in vertebrate and vascular plants, they may represent targets for novel therapeutic approaches based on the disruption of this key bacterial organic peroxide defense system.

Reactive oxygen species-inducing titanium peroxide nanoparticles as promising radiosensitizers for eliminating pancreatic cancer stem cells

BACKGROUND

Despite recent advances in radiotherapy, radioresistance in patients with pancreatic cancer remains a crucial dilemma for clinical treatment. Cancer stem cells (CSCs) represent a major factor in radioresistance. Developing a potent radiosensitizer may be a novel candidate for the eradication of pancreatic CSCs.

METHODS

CSCs were isolated from MIA PaCa-2 and PANC1 human pancreatic cancer cell lines. Titanium peroxide nanoparticles (TiOxNPs) were synthesized from titanium dioxide nanoparticles (TiO2NPs) and utilized as radiosensitizers when added one hour prior to radiation exposure. The antitumor activity of this novel therapeutic strategy was evaluated against well-established pancreatic CSCs model both in vitro and in vivo.

RESULTS

It is shown that TiOxNPs combined with ionizing radiation exhibit anti-cancer effects on radioresistant CSCs both in vitro and in vivo. TiOxNPs exhibited a synergistic effect with radiation on pancreatic CSC-enriched spheres by downregulating self-renewal regulatory factors and CSC surface markers. Moreover, combined treatment suppressed epithelial-mesenchymal transition, migration, and invasion properties in primary and aggressive pancreatic cancer cells by reducing the expression of proteins relevant to these processes. Notably, radiosensitizing TiOxNPs suppressed the growth of pancreatic xenografts following primary or dissociating sphere MIA PaCa-2 cell implantation. It is inferred that synergy is formed by generating intolerable levels of reactive oxygen species (ROS) and inactivating the AKT signaling pathway.

CONCLUSIONS

Our data suggested the use of TiOxNPs in combination with radiation may be considered an attractive therapeutic strategy to eliminate pancreatic CSCs.

Adiponectin ameliorates placental injury in gestational diabetes mice by correcting fatty acid oxidation/peroxide imbalance-induced ferroptosis via restoration of CPT-1 activity

PURPOSE

In gestational diabetes (GDM), abnormalities occur not only in glucose metabolism, but also in lipid metabolism. Adiponectin (ADPN) plays an important role in the regulation of lipid metabolism. In this paper, the role and mechanism of ADPN in GDM are discussed.

METHODS

GDM model was formed in pregnant mice induced by high-fat diet and streptozotocin, and blood glucose level was detected after ADPN treatment. The levels of TG, TC, HDL-C, and LDL-C in blood lipid of mice were detected by biochemical apparatus. HE staining was used to detect the placenta damage in mice. The expression of oxidative stress-related indexes in placental tissues was also detected by ELISA. Placental iron deposition was detected by Prussian blue staining. Redox capacity of placental tissue was detected by ELISA. Western blot was used to detect the expression of ferroptosis-related proteins in placental tissues. The expression of ADPN in placenta and peripheral blood was detected by ELISA, and the expression of ADPNR, downstream CPT-1, and GLUT4 of placenta were detected by RT-qPCR and western blot. Subsequently, trophoblast cells were induced by palmitic acid and glucose, and the cell activity was detected by CCK-8. The results in animal experiments were verified in cell experiments by RT-qPCR, western blot, and fluorescence labeling of iron ions. Finally, ADPN and CPT-1 inhibitor PM were given to trophoblast cells to further explore the mechanism.

RESULTS

ADPN inhibited blood glucose and lipid levels in GDM mice. ADPN inhibited oxidation/peroxide imbalance-induced ferroptosis in placental tissues of GDM mice. ADPN inhibited the expression of CPT-1 and GLUT4 in placental tissues of GDM mice. This result was also confirmed in cell experiments, and this process may be achieved by regulating CPT-1.

CONCLUSIONS

ADPN ameliorated placental injury in GDM by correcting fatty acid oxidation/peroxide imbalance-induced ferroptosis via restoration of CPT-1 activity.

Magnolol additive improves growth performance of Linwu ducklings by modulating antioxidative status

Magnolol is a bioactive polyphenolic compound commonly found in Magnolia officinalis. The aim of this study is to clarify the contribution of the magnolol additive on the growth performance of Linwu ducklings aging from 7 to 28 d, comparing to the effects of antibiotic additive (colistin sulphate). A total of 325, 7-d-old ducklings were assigned to 5 groups. Each group had 5 cages with 13 ducklings in each cage. The ducklings in different groups were fed with diets supplemented with 0, 100, 200 and 300 mg/kg magnolol additive (MA) (Control, MA100, MA200 and MA300) and 30 mg/kg colistin sulphate (CS30) for 3 weeks, respectively. Parameters regarding to the growth performance, intestinal mucosal morphology, serum biochemical indices, antioxidant and peroxide biomarkers and the expression levels of antioxidant-related genes were evaluated by one way ANOVA analysis. The results showed that 30 mg/kg colistin sulphate, 200 and 300 mg/kg magnolol additive improved the average final weight (P = 0.045), average daily body weight gain (P = 0.038) and feed/gain ratios (P = 0.001) compared to the control group. 200 and 300 mg/kg magnolol additive significantly increased the villus height/crypt depth ratio of ileum, compared to the control and CS30 groups (P = 0.001). Increased serum level of glucose (P = 0.011) and total protein (P = 0.006) were found in MA200 or MA300 group. In addition, comparing to the control and CS30 groups, MA200 or MA300 significantly increased the levels of superoxide dismutase (P = 0.038), glutathione peroxidase (P = 0.048) and reduced glutathione (P = 0.039) in serum. Moreover, the serum and hepatic levels of 8-hydroxy-2'-deoxyguanosine (P = 0.043 and 0.007, respectively) were lower in all MA groups compared to those of the control and CS30 group. The hepatic mRNA expression levels of superoxide dismutase-1, catalase and nuclear factor erythroid-2-related factor 2/erythroid-derived CNC-homology factor were also increased significantly in MA200 and MA300 groups (P < 0.05). Taken together, these data demonstrated that MA was an effective feed additive enhancing the growth performance of Linwu ducklings at 7 to 28 d by improving the antioxidant and intestinal mucosal status. It suggested that MA could be a potential ingredient to replace the colistin sulphate in diets.

The glutathionylation agent disulfiram augments superoxide/hydrogen peroxide production when liver mitochondria are oxidizing ubiquinone pool-linked and branched chain amino acid substrates

Our group has previously observed that protein S-glutathionylation serves as an integral feedback inhibitor for the production of superoxide (O₂^●-)/hydrogen peroxide (H₂O₂) by α-ketoglutarate dehydrogenase (KGDH), pyruvate dehydrogenase (PDH), and complex I in muscle and liver mitochondria, respectively. In the present study, we hypothesized that glutathionylation would fulfill a similar role for the O₂^●-/H₂O₂ sources sn-glycerol-3-phosphate dehydrogenase (G3PDH), proline dehydrogenase (PRODH), and branched chain keto acid dehydrogenase (BCKDH). Surprisingly, we found that inducing glutathionylation with disulfiram increased the production of O₂^●-/H₂O₂ by mitochondria oxidizing glycerol-3-phosphate (G3P), proline (Pro), or α-keto-β-methylvaleric acid (KMV). Treatment of mitochondria oxidizing G3P or Pro with rotenone or myxothiazol increased the rate of ROS production after incubating in 1000 nM disulfiram. Incubating mitochondria treated with disulfiram in both rotenone and myxothiazol prevented this increase in O₂^●-/H₂O₂ production. In addition, when adminstered together, ROS production decreased below control levels. Disulfiram-treated mitochondria displayed higher rates of ROS production when oxidizing succinate, which was inhibited by rotenone, myxothiazol, and malonate, respectively. Disulfiram also increased ROS production by mitocondria oxidizing KMV. Treatment of mitochondria oxidizing KMV with disulfiram and rotenone or myxothiazol did not alter the rate O₂^●-/H₂O₂ production further when compared to mitochondria treated with disulfiram only. Analysis of BCKDH activity following disulfiram treatment revealed that glutathionylation does not inhibit the enzyme complex, indicating this α-keto acid dehydrogenase is not a target for glutathione modification. However, treatment of mitochondria with rotenone and myxothiazol without disulfiram also augmented ROS production. Overall, we were able to demonstrate for the first time that glutathionylation augments ROS production by the respiratory chain during forward electron transfer (FET) and reverse electron transfer (RET) from the UQ pool. Additionally, we were able to show that BCKDH is not a target for glutathione modification and that glutathionylation can also increase ROS production in mitochondria oxidizing branched chain amino acids following the modification of enzymes upstream of BCKDH.

Molecular insights into the endoperoxide formation by Fe(II)/α-KG-dependent oxygenase NvfI

Endoperoxide-containing natural products are a group of compounds with structurally unique cyclized peroxide moieties. Although numerous endoperoxide-containing compounds have been isolated, the biosynthesis of the endoperoxides remains unclear. NvfI from Aspergillus novofumigatus IBT 16806 is an endoperoxidase that catalyzes the formation of fumigatonoid A in the biosynthesis of novofumigatonin. Here, we describe our structural and functional analyses of NvfI. The structural elucidation and mutagenesis studies indicate that NvfI does not utilize a tyrosyl radical in the reaction, in contrast to other characterized endoperoxidases. Further, the crystallographic analysis reveals significant conformational changes of two loops upon substrate binding, which suggests a dynamic movement of active site during the catalytic cycle. As a result, NvfI installs three oxygen atoms onto a substrate in a single enzyme turnover. Based on these results, we propose a mechanism for the NvfI-catalyzed, unique endoperoxide formation reaction to produce fumigatonoid A.

PICK1 Deficiency Exacerbates Sepsis-Associated Acute Kidney Injury

We performed in vitro and in vivo experiments to explore the role of protein kinase C-binding protein 1 (PICK1), an intracellular transporter involved in oxidative stress-related neuronal diseases, in sepsis-related acute kidney injury (AKI). Firstly, PCR, western blotting, and immunohistochemistry were used to observe the expression of PICK1 after lipopolysaccharide- (LPS-) induced AKI. Secondly, by inhibiting PICK1 in vivo and silencing PICK1 in vitro, we further explored the effect of PICK1 on AKI. Finally, the relationship between PICK1 and oxidative stress and the related mechanisms were explored. We found that the expression of PICK1 was increased in LPS-induced AKI models both in vitro and in vivo. PICK1 silencing significantly aggravated LPS-induced apoptosis, accompanied by ROS production in renal tubular epithelial cells. FSC231, a PICK1-specific inhibitor, aggravated LPS-induced kidney injury. Besides, NAC (N-acetylcysteine), a potent ROS scavenger, significantly inhibited the PICK1-silencing-induced apoptosis. In conclusion, PICK1 might protect renal tubular epithelial cells from LPS-induced apoptosis by reducing excessive ROS, making PICK1 a promising preventive target in LPS-induced AKI.

Cu-Ferrocene-Functionalized CaO2 Nanoparticles to Enable Tumor-Specific Synergistic Therapy with GSH Depletion and Calcium Overload

The conversion of endogenous H2 O2 into toxic hydroxyl radical (• OH) via catalytic nanoparticles is explored for tumor therapy and received considerable success. The intrinsic characteristics of microenvironment in tumor cells, such as limited H2 O2 and overexpressed glutathione (GSH), hinder the intracellular • OH accumulation and thus weaken therapeutic efficacy considerably. In this study, fine CaO2 nanoparticles with Cu-ferrocene molecules at the surface (CaO2 /Cu-ferrocene) are successfully designed and synthesized. Under an acidic condition, the particles release Ca2+ ions and H2 O2 in a rapid fashion, while they can remain stable in neutral. In addition, agitated production of • OH occurs following the Fenton reaction of H2 O2 and ferrocene molecules, and GSH is consumed by Cu2+ ions to avoid the potential • OH consumption. More interestingly, in addition to the exogenous Ca2+ released by the particles, the enhanced • OH production facilitates intracellular calcium accumulation by regulating Ca2+ channels and pumps of tumor cells. It turns out that promoted • OH induction and intracellular calcium overload enable significant in vitro and in vivo antitumor phenomena.

Synthesis of Caffeoyl-Prolyl-Histidyl-Xaa Derivatives and Evaluation of Their Activities and Stability upon Long-Term Storage

Antioxidants play a critical role in the treatment of degenerative diseases and delaying the aging of dermal tissue. Caffeic acid (CA) is a representative example of the antioxidants found in plants. However, CA is unsuitable for long-term storage because of its poor stability under ambient conditions. Caffeoyl-Pro-His-NH₂ (CA-Pro-His-NH₂, CA-PH) exhibits the highest antioxidant activity, free radical scavenging and lipid peroxidation inhibition activity among the histidine-containing CA-conjugated dipeptides reported to date. The addition of short peptides to CA, such as Pro-His, is assumed to synergistically enhance its antioxidative activity. In this study, several caffeoyl-prolyl-histidyl-Xaa-NH₂ derivatives were synthesized and their antioxidative activities evaluated. CA-Pro-His-Asn-NH₂ showed enhanced antioxidative activity and higher structural stability than CA-PH, even after long-term storage. CA-Pro-His-Asn-NH₂ was stable for 3 months, its stability being evaluated by observing the changes in its NMR spectra. Moreover, the solid-phase synthetic strategy used to prepare these CA-Pro-His-Xaa-NH₂ derivatives was optimized for large-scale production. We envision that CA-Pro-His-Xaa-NH₂ derivatives can be used as potent dermal therapeutic agents and useful cosmetic ingredients.

The Onset of Systemic Oxidative Stress Associated with the Accumulation of Lipid Peroxidation Product Acrolein in the Skin of Patients with Small-Vessel Vasculitis

Small-vessel vasculitis (SVV) is the inflammation of the vessel wall that can result in hemorrhage and/or ischemia. Among the histological findings in SVV are increased infiltrating neutrophils, which, due to their oxidative burst and myeloperoxidase activity, release excessive reactive oxygen species, triggering a chain reaction of lipid peroxidation and yielding reactive aldehydes such as acrolein. The implication of oxidative stress in the pathogenesis of SVV was studied, focusing on acrolein immunohistochemistry in the affected skin vessels and systemic stress response. Samples from SVV patients and healthy subjects were collected and analyzed for total serum peroxides, total antioxidant capacity, inflammatory and immunological parameters, as well as for the presence of acrolein–protein adducts in the skin tissue specimens. The obtained data showed that systemic redox homeostasis and iron metabolism are altered in SVV patients. Possible biomarkers in the evaluation of oxidative status, disease activity and prevalence were indicated. Furthermore, a strong correlation between the accumulation of acrolein–protein adducts in the skin and the progression of the disease was revealed. Thus, the results of this study demonstrate that SVV is not only associated with systemic oxidative stress but also with tissue-specific oxidative stress that promotes acrolein formation and protein modification correlating with the severity of cutaneous vasculitis.

Adaptation of Dinoroseobacter shibae to oxidative stress and the specific role of RirA

Dinoroseobacter shibae living in the photic zone of marine ecosystems is frequently exposed to oxygen that forms highly reactive species. Here, we analysed the adaptation of D. shibae to different kinds of oxidative stress using a GeLC-MS/MS approach. D. shibae was grown in artificial seawater medium in the dark with succinate as sole carbon source and exposed to hydrogen peroxide, paraquat or diamide. We quantified 2580 D. shibae proteins. 75 proteins changed significantly in response to peroxide stress, while 220 and 207 proteins were differently regulated by superoxide stress and thiol stress. As expected, proteins like thioredoxin and peroxiredoxin were among these proteins. In addition, proteins involved in bacteriochlophyll biosynthesis were repressed under disulfide and superoxide stress but not under peroxide stress. In contrast, proteins associated with iron transport accumulated in response to peroxide and superoxide stress. Interestingly, the iron-responsive regulator RirA in D. shibae was downregulated by all stressors. A rirA deletion mutant showed an improved adaptation to peroxide stress suggesting that RirA dependent proteins are associated with oxidative stress resistance. Altogether, 139 proteins were upregulated in the mutant strain. Among them are proteins associated with protection and repair of DNA and proteins (e. g. ClpB, Hsp20, RecA, and a thioredoxin like protein). Strikingly, most of the proteins involved in iron metabolism such as iron binding proteins and transporters were not part of the upregulated proteins. In fact, rirA deficient cells were lacking a peroxide dependent induction of these proteins that may also contribute to a higher cell viability under these conditions.

Ferric Heme Superoxide Reductive Transformations to Ferric Heme (Hydro)Peroxide Species: Spectroscopic Characterization and Thermodynamic Implications for H-Atom Transfer (HAT)

A new end-on low-spin ferric heme peroxide, [(PIm )FeIII -(O22- )]- (PIm -P), and subsequently formed hydroperoxide species, [(PIm )FeIII -(OOH)] (PIm -HP) are generated utilizing the iron-porphyrinate PIm with its tethered axial base imidazolyl group. Measured thermodynamic parameters, the ferric heme superoxide [(PIm )FeIII -(O2⋅- )] (PIm -S) reduction potential (E°') and the PIm -HP pKa value, lead to the finding of the OO-H bond-dissociation free energy (BDFE) of PIm -HP as 69.5 kcal mol-1 using a thermodynamic square scheme and Bordwell relationship. The results are validated by the observed oxidizing ability of PIm -S via hydrogen-atom transfer (HAT) compared to that of the F8 superoxide complex, [(F8 )FeIII -(O2.- )] (S) (F8 =tetrakis(2,6-difluorophenyl)porphyrinate, without an internally appended axial base imidazolyl), as determined from reactivity comparison of superoxide complexes PIm -S and S with the hydroxylamine (O-H) substrates TEMPO-H and ABNO-H.

The transcriptional response of pathogenic Leptospira to peroxide reveals new defenses against infection-related oxidative stress

Pathogenic Leptospira spp. are the causative agents of the waterborne zoonotic disease leptospirosis. Leptospira are challenged by numerous adverse conditions, including deadly reactive oxygen species (ROS), when infecting their hosts. Withstanding ROS produced by the host innate immunity is an important strategy evolved by pathogenic Leptospira for persisting in and colonizing hosts. In L. interrogans, genes encoding defenses against ROS are repressed by the peroxide stress regulator, PerR. In this study, RNA sequencing was performed to characterize both the L. interrogans response to low and high concentrations of hydrogen peroxide and the PerR regulon. We showed that Leptospira solicit three main peroxidase machineries (catalase, cytochrome C peroxidase and peroxiredoxin) and heme to detoxify oxidants produced during peroxide stress. In addition, canonical molecular chaperones of the heat shock response and DNA repair proteins from the SOS response were required for Leptospira recovering from oxidative damage. Identification of the PerR regulon upon exposure to H₂O₂ allowed to define the contribution of this regulator in the oxidative stress response. This study has revealed a PerR-independent regulatory network involving other transcriptional regulators, two-component systems and sigma factors as well as non-coding RNAs that putatively orchestrate, in concert with PerR, the oxidative stress response. We have shown that PerR-regulated genes encoding a TonB-dependent transporter and a two-component system (VicKR) are involved in Leptospira tolerance to superoxide. This could represent the first defense mechanism against superoxide in L. interrogans, a bacterium lacking canonical superoxide dismutase. Our findings provide an insight into the mechanisms required by pathogenic Leptospira to overcome oxidative damage during infection-related conditions. This will participate in framing future hypothesis-driven studies to identify and decipher novel virulence mechanisms in this life-threatening pathogen.

Leptospirosis is a zoonotic infectious disease responsible for over one million of severe cases and 60 000 fatalities annually worldwide. This neglected and emerging disease has a worldwide distribution, but it mostly affects populations from developing countries in sub-tropical areas. The causative agents of leptospirosis are pathogenic bacterial Leptospira spp. There is a considerable deficit in our knowledge of these atypical bacteria, including their virulence mechanisms. During infection, Leptospira are confronted with the deadly oxidants produced by the host tissues and immune response. Here, we have identified the leptospiral factors necessary for overcoming infection-related oxidative stress. We found that Leptospira solicit peroxidases to detoxify oxidants as well as chaperones of the heat shock response and DNA repair proteins of the SOS response to recover from oxidative damage. Moreover, our study indicates that the oxidative stress response is orchestrated by a regulatory network involving PerR and other transcriptional regulators, sigma factors, two component systems, and putative non-coding RNAs. These findings provide insights into the mechanisms required by pathogenic Leptospira to tolerate infection-related oxidants and could help identifying novel virulence factors and developing new therapeutic targets.

Hepatitis B virus surface protein induces oxidative stress by increasing peroxides and inhibiting antioxidant defences in human spermatozoa

Hepatitis B virus (HBV) infection may affect sperm motility in patients with HBV. HBV surface protein (HBs) decreases mitochondrial membrane potential, impairs motility and induces apoptotic-like changes in human spermatozoa. However, little is known about how human spermatozoa respond to reactive oxygen species (ROS; mainly peroxides) induced by HBs. In this study, HBs induced supraphysiological ROS levels in human spermatozoa and reduced the formation of 2-cell embryos (obtained from hamster oocytes and human spermatozoa). HBs induced a pre-apoptotic status in human spermatozoa, as well as antioxidant defences by increasing glutathione peroxidase 4 (GPX4) and peroxiredoxin 5 (PRDX5) levels. These results highlight the molecular mechanism responsible for the oxidative stress in human spermatozoa exposed to HBV and the antioxidant defence response involving GPX4 and PRDX5.

CYP20-3 deglutathionylates 2-CysPRX A and suppresses peroxide detoxification during heat stress

In plants, growth-defense trade-offs occur because of limited resources, which demand prioritization towards either of them depending on various external and internal factors. However, very little is known about molecular mechanisms underlying their occurrence. Here, we describe that cyclophilin 20-3 (CYP20-3), a 12-oxo-phytodienoic acid (OPDA)-binding protein, crisscrosses stress responses with light-dependent electron reactions, which fine-tunes activities of key enzymes in plastid sulfur assimilations and photosynthesis. Under stressed states, OPDA, accumulates in the chloroplasts, binds and stimulates CYP20-3 to convey electrons towards serine acetyltransferase 1 (SAT1) and 2-Cys peroxiredoxin A (2CPA). The latter is a thiol-based peroxidase, protecting and optimizing photosynthesis by reducing its toxic byproducts (e.g., H2O2). Reduction of 2CPA then inactivates its peroxidase activity, suppressing the peroxide detoxification machinery, whereas the activation of SAT1 promotes thiol synthesis and builds up reduction capacity, which in turn triggers the retrograde regulation of defense gene expressions against abiotic stress. Thus, we conclude that CYP20-3 is a unique metabolic hub conveying resource allocations between plant growth and defense responses (trade-offs), ultimately balancing optimal growth phonotype.

Chlorothalonil causes redox state change leading to oxidative stress generation in Danio rerio

A diverse range of chemicals are used in agriculture to increase food production on a large scale, and among them is the use of pesticides such as chlorothalonil, a broad-spectrum fungicide used in the control of foliar fungal diseases. This study aimed to elucidate the effects of chlorothalonil on biochemical biomarkers of oxidative stress in tissues of the fish Danio rerio. To achieve this, animals were exposed for 4 and 7 days, to nominal concentrations of chlorothalonil at 0 μg/L (DMSO, 0.001%), 0.1 μg/L and 10 μg/L, and after the exposure period, the tissues (gills and liver) were removed for biochemical analysis. Antioxidant capacity against peroxyl radicals (ACAP) and enzyme activities, such as superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST) and glutamate cysteine ligase (GCL), were evaluated in both tissues. In addition, the concentration of reactive oxygen species (ROS), reduced glutathione (GSH) and lipid peroxidation (LPO) levels were also analysed. A significant increase in ROS concentration, ACAP levels, GST and GCL activities and a significant reduction of LPO levels in gills exposed to the highest concentration were observed after 4 days. However, there was a significant reduction of ACAP and CAT activity, as well as a significant increase of GST activity and LPO levels in gills exposed to the lower concentration after 7 days. The liver was less affected, presenting a significant reduction in CAT activity and LPO levels after 4 days. However, a significant increase in SOD activity and LPO levels occurred after 7 days. These results indicate that chlorothalonil, after 4 days, caused activation of the antioxidant defence system in gills of animals exposed to the highest concentration. However, after 7 days, the lowest concentration of this compound caused oxidative stress in this same organ. Also, the results show that gills were more affected than the liver, probably because gills can be involved in chlorothalonil metabolisation. Therefore, it is possible that the liver could be exposed to lower chlorothalonil concentrations or less toxic metabolites due to the metabolism taking place in the gills.

ROS regulation of RAS and vulva development in Caenorhabditis elegans

Reactive oxygen species (ROS) are signalling molecules whose study in intact organisms has been hampered by their potential toxicity. This has prevented a full understanding of their role in organismal processes such as development, aging and disease. In Caenorhabditis elegans, the development of the vulva is regulated by a signalling cascade that includes LET-60ras (homologue of mammalian Ras), MPK-1 (ERK1/2) and LIN-1 (an ETS transcription factor). We show that both mitochondrial and cytoplasmic ROS act on a gain-of-function (gf) mutant of the LET-60ras protein through a redox-sensitive cysteine (C118) previously identified in mammals. We show that the prooxidant paraquat as well as isp-1, nuo-6 and sod-2 mutants, which increase mitochondrial ROS, inhibit the activity of LET-60rasgf on vulval development. In contrast, the antioxidant NAC and loss of sod-1, both of which decrease cytoplasmic H202, enhance the activity of LET-60rasgf. CRISPR replacement of C118 with a non-oxidizable serine (C118S) stimulates LET-60rasgf activity, whereas replacement of C118 with aspartate (C118D), which mimics a strongly oxidised cysteine, inhibits LET-60rasgf. These data strongly suggest that C118 is oxidized by cytoplasmic H202 generated from dismutation of mitochondrial and/or cytoplasmic superoxide, and that this oxidation inhibits LET-60ras. This contrasts with results in cultured mammalian cells where it is mostly nitric oxide, which is not found in worms, that oxidizes C118 and activates Ras. Interestingly, PQ, NAC and the C118S mutation do not act on the phosphorylation of MPK-1, suggesting that oxidation of LET-60ras acts on an as yet uncharacterized MPK-1-independent pathway. We also show that elevated cytoplasmic superoxide promotes vulva formation independently of C118 of LET-60ras and downstream of LIN-1. Finally, we uncover a role for the NADPH oxidases (BLI-3 and DUOX-2) and their redox-sensitive activator CED-10rac in stimulating vulva development. Thus, there are at least three genetically separable pathways by which ROS regulates vulval development.

Transformation of amino acid tyrosine in chromophoric organic matter solutions: Generation of peroxide and change of bioavailability

Studying the photochemical transformation mechanism of dissolved free amino acids (DFAA) in chromophoric dissolved organic matter (CDOM) solution facilitates the understanding of DFAA's environmental fate and bioavailability change upon solar irradiation in natural surface waters. Tyrosine oxidation product (Tyr-OH) was synthesized to quantify the primary transformation product (tyrosine peroxide, Tyr-OOH) in CDOM solution. Both reactions between superoxide radical anion (O₂^-) and tyrosine radical (Tyr) and between singlet oxygen (¹O₂) and tyrosine (Tyr) yield Tyr-OOH, which is subsequently transformed into Tyr-OH. The reaction between O₂^- and Tyr not only generated Tyr-OOH but also caused the regeneration of Tyr. O₂^- and ¹O₂ contributed 30-44% to Tyr's transformation in CDOM solutions at pH 8.0, in which ¹O₂ oxidation accounted for 6-11%. The contribution of O₂^- to Tyr's phototransformation process was the difference between the total contribution of O₂^- and ¹O₂ and the individual contribution of ¹O₂. Compared with the fast assimilation of Tyr, Tyr-OH was stable in natural water under dark incubation, indicating that phototransformation decreased the bioavailability of Tyr.

Oxidative stress: Noradrenaline as an integrator of responses in the neuroendocrine and immune systems of the ascidian Phallusia nigra

Neurotransmitters play key roles in regulating the homeostasis of organisms in stressful environments. Noradrenaline (NA) is the main neurotransmitter known to modulate immunological parameters, and is important in the crosstalk between the neuroendocrine and immune systems. In this study, using the ascidian Phallusia nigra, we analyzed the level of catecholamines (CA) in the plasma after mechanical stress, and the effect of NA on the oxidative stress (OS) displayed by immune cells. We measured the concentration of reactive oxygen species (ROS), and analyzed whether α- and/or β-adrenoreceptors (ARs) are involved in ROS modulation, lipid peroxidation (LPO), antioxidant capacity against peroxyl radicals (ACAP), and activity of the enzymes catalase (CAT) and glutathione S transferase (GST) in immune cells after incubation with different concentrations of NA, with or without zymosan (ZnA) challenge. The results showed that NA reduced ROS production, even in immune cells challenged with ZnA, and that this modulation occurred through α₁-and β₁-ARs. ACAP levels showed different responses, depending on whether immune cells were challenged or not with ZnA, and also depending on the NA concentration: 1.0 μM NA increased ACAP levels, but 10.0 μM reduced ACAP levels. NA enhanced the activity of CAT and GST in ZnA-challenged and non-challenged immune cells, while 1.0 and 10.0 μM NA effectively reduced LPO. Taken together, these results show that NA can protect cells from ROS damage, decreasing ROS production and LPO, and enhancing ACAP as well as the activity of CAT and GST. The approach used here with this model contributes to understanding the relationship between the neuroendocrine and immune systems, revealing new effects of NA on OS regulation in ascidians.

Activation of artemisinin and heme degradation in Leishmania tarentolae promastigotes: A possible link

Endoperoxides (EPs) appear to be promising drug candidates against protozoal diseases, including malaria and leishmaniasis. Previous studies have shown that these drugs need an intracellular activation to exert their pharmacological potential. The efficiency of these drugs is linked to the extensive iron demand of these intracellular protozoal parasites. An essential step of the activation mechanism of these drugs is the formation of radicals in Leishmania. Iron is a known trigger for intracellular radical formation. However, the activation of EPs by low molecular iron or by heme iron may strongly depend on the structure of the EPs themselves. In this study, we focused on the activation of artemisinin (Art) in Leishmania tarentolae promastigotes (LtP) in comparison to reference compounds. Viability assays in different media in the presence of different iron sources (hemin/fetal calf serum) showed that IC50 values of Art in LtP were modulated by assay conditions, but overall were within the low micromolar range. Low temperature electron paramagnetic resonance (EPR) spectroscopy of LtP showed that Art shifted the redox state of the labile iron pool less than the EP ascaridole questioning its role as a major activator of Art in LtP. Based on the high reactivity of Art with hemin in previous biomimetic experiments, we focused on putative heme-metabolizing enzymes in Leishmania, which were so far not well described. Inhibitors of mammalian heme oxygenase (HO; tin and chromium mesoporphyrin) acted antagonistically to Art in LtP and boosted its IC50 value for several magnitudes. By inductively coupled plasma methods (ICP-OES, ICP-MS) we showed that these inhibitors do not block iron (heme) accumulation, but are taken up and act within LtP. These inhibitors blocked the conversion of hemin to bilirubin in LtP homogenates, suggesting that an HO-like enzyme activity in LtP exists. NADPH-dependent degradation of Art and hemin was highest in the small granule and microsomal fractions of LtP. Photometric measurements in the model Art/hemin demonstrated that hemin requires reduction to heme and that subsequently an Art/heme complex (λmax 474 nm) is formed. EPR spin-trapping in the system Art/hemin revealed that NADPH, ascorbate and cysteine are suitable reductants and finally activate Art to acyl-carbon centered radicals. These findings suggest that heme is a major activator of Art in LtP either via HO-like enzyme activities and/or chemical interaction of heme with Art.

Multi-sensor integration approach based on hyperspectral imaging and electronic nose for quantitation of fat and peroxide value of pork meat

The study assessed the feasibility of merging data acquired from hyperspectral imaging (HSI) and electronic nose (e-nose) to develop a robust method for the rapid prediction of intramuscular fat (IMF) and peroxide value (PV) of pork meat affected by temperature and NaCl treatments. Multivariate calibration models for prediction of IMF and PV using median spectra features (MSF) and image texture features (ITF) from HSI data and mean signal values (MSV) from e-nose signals were established based on support vector machine regression (SVMR). Optimum wavelengths highly related to IMF and PV were selected from the MSF and ITF. Next, recurring optimum wavelengths from the two feature groups were manually obtained and merged to constitute "combined attribute features" (CAF) which yielded acceptable results with (R_c² = 0.877, 0.891; RMSEC = 2.410, 1.109; R_p² = 0.790, 0.858; RMSEP = 3.611, 2.013) respectively for IMF and PV. MSV yielded relatively low results with (R_c² = 0.783, 0.877; RMSEC = 4.591, 0.653; R_p² = 0.704, 0.797; RMSEP = 3.991, 0.760) respectively for IMF and PV. Finally, data fusion of CAF and MSV was performed which yielded relatively improved prediction results with (R_c² = 0.936, 0.955; RMSEC = 1.209, 0.997; R_p² = 0.895, 0.901; RMSEP = 2.099, 1.008) respectively for IMF and PV. The results obtained demonstrate that it is feasible to mutually integrate spectral and image features with volatile information to quantitatively monitor IMF and PV in processed pork meat. Graphical abstract.

Deciphering the in vivo redox behavior of human peroxiredoxins I and II by expressing in budding yeast

Peroxiredoxins (Prxs), scavenge cellular peroxides by forming recyclable disulfides but under high oxidative stress, hyperoxidation of their active-site Cys residue results in loss of their peroxidase activity. Saccharomyces cerevisiae deficient in human Prx (hPrx) orthologue TSA1 show growth defects under oxidative stress. They can be complemented with hPRXI but not by hPRXII, but it is not clear how the disulfide and hyperoxidation states of the hPrx vary in yeast under oxidative stress. To understand this, we used oxidative-stress sensitive tsa1tsa2Δ yeast strain to express hPRXI or hPRXII. We found that hPrxI in yeast exists as a mixture of disulfide-linked dimer and reduced monomer but becomes hyperoxidized upon elevated oxidative stress as analyzed under denaturing conditions (SDS-PAGE). In contrast, hPrxII was present predominantly as the disulfide in unstressed cells and readily converted to its hyperoxidized, peroxidase-inactive form even with mild oxidative stress. Interestingly, we found that plant extracts containing polyphenol antioxidants provided further protection against the growth defects of the tsa1tsa2Δ strain expressing hPrx and preserved the peroxidase-active forms of the Prxs. The extracts also helped to protect against hyperoxidation of hPrxs in HeLa cells. Based on these findings we can conclude that resistance to oxidative stress of yeast cells expressing individual hPrxs requires the hPrx to be maintained in a redox state that permits redox cycling and peroxidase activity. Peroxidase activity decreases as the hPrx becomes hyperoxidized and the limited protection by hPrxII compared with hPrxI can be explained by its greater sensitivity to hyperoxidation.

Melatonin Inhibits Peroxide Production in Plant Mitochondria

The effect of melatonin on respiration and production (release) of hydrogen peroxide during succinate oxidation in mitochondria isolated from lupine cotyledons and epicotyls of pea seedlings was studied. It was shown for the first time that melatonin (10-7-10-3 M) had a significant inhibitory effect on the production of peroxide by plant mitochondria, which was characterized by concentration dependence and species specificity. At the same time, melatonin (at a concentration of up to 100 μM) had virtually no effect on mitochondrial respiration rate and respiratory control coefficient. The results confirm the antioxidant function of melatonin and indicate that it is involved in the regulation of ROS levels and maintenance of redox balance in plant mitochondria.

Differential oxidation processes of peroxiredoxin 2 dependent on the reaction with several peroxides in human red blood cells

Peroxiredoxins (Prxs) detoxify hydrogen peroxide (H₂O₂), peroxynitrite, and various organic hydroperoxides. However, the differential oxidative status of Prxs reacted with each peroxide remains unclear. In the present study, we focused on the oxidative alteration of Prxs and demonstrated that, in human red blood cells (RBCs), peroxiredoxin 2 (Prx2) is readily reactive with H₂O₂, forming disulfide dimers, but was not easily hyperoxidized. In contrast, Prx2 was highly sensitive to the relatively hydrophobic oxidants, such as tert-butyl hydroperoxide (t-BHP) and cumene hydroperoxide. These peroxides hyperoxidized Prx2 into oxidatively damaged forms in RBCs. The t-BHP treatment formed hyperoxidized Prx2 in a dose-dependent manner. When organic hydroperoxide-treated RBC lysates were subjected to reverse-phase high performance liquid chromatography, two peaks derived from hyperoxidized Prx2 appeared along with the decrease of that corresponding to native Prx2. Liquid chromatography-tandem mass spectrometry analysis clearly showed that hyperoxidation to sulfonic acid (-SO₃H) at Cys-51 residue was more advanced in a newfound hyperoxidized Prx2 compared to another hydrophobic hyperoxidized form previously identified. These results indicate that irreversible hyperoxidation of the Prx2 monomer in RBCs was easily caused by organic hydroperoxide but not H₂O₂. Thus, it is important to detect the hyperoxidation of Prx2 into sulfinic or sulfonic acid derivates of Cys-51 because hyperoxidized Prx2 is a potential marker of oxidative injury caused by organic hydroperoxides in human RBCs.

Unraveling the effects of peroxiredoxin 2 nitration; role of C-terminal tyrosine 193

Peroxiredoxins (Prx) are enzymes that efficiently reduce hydroperoxides through active participation of cysteine residues (C_P, C_R). The first step in catalysis, the reduction of peroxide substrate, is fast, 10⁷ - 10⁸ M^-1s^-1 for human Prx2. In addition, the high intracellular concentration of Prx positions them not only as good antioxidants but also as central players in redox signaling pathways. These biological functions can be affected by post-translational modifications that could alter the peroxidase activity and/or interaction with other proteins. In particular, inactivation by hyperoxidation of C_P, which occurs when a second molecule of peroxide reacts with the C_P in the sulfenic acid form, modulates their participation in redox signaling pathways. The higher sensitivity to hyperoxidation of some Prx has been related to the presence of structural motifs that disfavor disulfide formation at the active site, making the C_P sulfenic acid more available for hyperoxidation or interaction with a redox protein target. We previously reported that treatment of human Prx2 with peroxynitrite results in tyrosine nitration, a post-translational modification on non-catalytic residues, yielding a more active peroxidase with higher resistance to hyperoxidation. In this work, studies on various mutants of hPrx2 confirm that the presence of the tyrosyl side-chain of Y193, belonging to the C-terminal YF motif of eukaryotic Prx, is necessary to observe the increase in Prx2 resistance to hyperoxidation. Moreover, our results underline the critical role of this structural motif on the rate of disulfide formation that determines the differential participation of Prx in redox signaling pathways.

Bioremediation of benzene-contaminated groundwater by calcium peroxide (CaO2) nanoparticles: Continuous-flow and biodiversity studies

Calcium peroxide (CaO₂) nanoparticles have been extensively applied in treatment of contaminated groundwater through bioremediation or modified Fenton (MF) processes. In the present study utilization of CaO₂ in bioremediation and MF (CaO₂+FeSO₄) reaction is investigated for benzene (50 mg/L) removal in continuous flow sand-packed columns. The results indicated that MF produced OH radicals markedly increased benzene remediation at first 30 days (up to 93%). But, OH generation rate was gradually declined when the pH was increased and finally 75% of initial benzene removed after 100d. In bioremediation column, because of supplying adequate oxygen by CaO₂, the number of planktonic bacteria logarithmically increased to more than 5 × 10⁶ CFU/mL (two orders of magnitude) and consequently 100% benzene removal was achieved by the end of experiment. Scanning electron microscopy analysis visualized the attached biofilm growth on sand surfaces in CaO₂ injected columns indicating their key role in the remediation process. The impact of each process on the microbial biodiversity of groundwater was investigated by next generation sequencing (NGS) of the 16S rRNA gene. The alpha and beta analysis indicated that microbial diversity is decreased by CaO₂ injection while benzene-degrading species such as Silanimonas, Arthrobacter and Pseudomonas spp. were dominated in remediation column.

CeVO4 Nanozymes Catalyze the Reduction of Dioxygen to Water without Releasing Partially Reduced Oxygen Species

In this study, we report a remarkably active CeVO₄ nanozyme that functionally mimics cytochrome c oxidase (CcO), the terminal enzyme in the respiratory electron transport chain, by catalyzing a four-electron reduction of dioxygen to water. The nanozyme catalyzes the reaction by using cytochrome c (Cyt c), the biological electron donor for CcO, at physiologically relevant pH. The CcO activity of the CeVO₄ nanozymes depends on the relative ratio of surface Ce³⁺ /Ce⁴⁺ ions, the presence of V⁵⁺ and the surface-Cyt c interactions. The complete reduction of oxygen to water takes place without release of any partially reduced oxygen species (PROS) such as superoxide, peroxide and hydroxyl radicals.

Comparison of inert and non-inert cathode in cathode/Fe3+/Peroxymonosulfate processes on iohexol degradation

To investigate the effect of cathode materials on organics degradation in a cathode/Fe³⁺/PMS process, different cathode materials (platinum, copper and iron) were selected and their performances were compared with iohexol as target organics. The optimal conditions were found to be different for different cathode/Fe³⁺/PMS processes. With a relatively high cathodic current input (2.0 mA/cm²), similar results were found for all the three cathode/Fe³⁺/PMS processes. With a small cathodic current input (not higher than 1.0 mA/cm²), the iohexol removal followed the order of Fe-cathode/Fe³⁺/PMS > Cu-cathode/Fe³⁺/PMS > Pt-cathode/Fe³⁺/PMS, due to the corrosion of Cu-cathode and Fe-cathode and the more serious corrosion of Fe-cathode than Cu-cathode. The corrosion of non-inert cathode materials (Cu-cathode and Fe-cathode) meant that these cathodes not only transmitted electrons but also participated in aqueous reactions, which complicated the mechanisms of cathode/Fe³⁺/PMS processes. The radical identification experiments indicated that SO₄^- was more important than OH for iohexol degradation in Cu-cathode/Fe³⁺/PMS process, while OH played a major role in Pt-cathode/Fe³⁺/PMS and Fe-cathode/Fe³⁺/PMS processes. The different reaction mechanisms resulted in different iohexol transformation pathways in cathode/Fe³⁺/PMS processes with different cathode materials.

Upregulation of peroxide scavenging enzymes and multidrug efflux proteins highlight an active sodium hypochlorite response in Pseudomonas fluorescens biofilms

The oxidative biocide sodium hypochlorite is among the most commonly used antimicrobial agents in the control of surface-attached microbial communities (biofilms). Clarifying the genetic response of microorganisms in biofilms to hypochlorite may contribute to improved biofilm control strategies. Here, RNA-seq was used to investigate the differential gene expression response of industrially relevant Pseudomonas fluorescens biofilms to sub-lethal concentrations of sodium hypochlorite. Pseudomonas biofilms responded to hypochlorite exposure with increased transcription of genes encoding peroxide scavenging enzymes (e.g., alkyl hydroperoxide reductase (Ahp) and hydroperoxide resistance protein (Ohr)), oxidative stress repair enzymes (e.g., the periplasmic sulfoxide reductase YedYZ complex), and multidrug efflux (e.g., MexEF pumps). In addition, genes involved in amino acid synthesis and energy metabolism were down-regulated following hypochlorite exposure. This work improves the current understanding of genetic response mechanisms to biocides and contributes to the optimization of biocides and application strategies.

Effect of antioxidant supplements on lipid peroxidation levels in primary cortical neuron cultures

Oxidative stress, specifically lipid peroxidation, is a major driving force in neurodegenerative processes. However, the exact role of lipid peroxidation remains elusive as reliable real-time detection and quantification of lipid peroxyl radicals proves to be challenging in vitro and in vivo. Motivated by this methodological limitation, we have optimized conditions for real-time imaging and quantification of lipid peroxyl radical generation in primary neuron cultures using the lipophilic fluorogenic antioxidant H₄BPMHC (8-((6-hydroxy-2,5,7,8-tetramethylchroman-2-yl)-methyl)-1,5-di(3-chloropropyl)-pyrromethene fluoroborate), an α-tocopherol analog probe. By subjecting neurons to different antioxidant conditions in the presence and absence of lipid peroxidation inducing stressors (Haber-Weiss reagents), we maximized H₄BPMHC sensitivity and confirmed its potential to temporally resolve subtle and marked differences in lipid peroxidation levels in real-time. Herein we report imaging and quantification of homeostatic and induced lipid peroxidation in primary neuron cultures, supporting the use of this probe for investigating healthy and diseased states. Overall these results provide the necessary foundation and impetus towards using H₄BPMHC for elucidating and mapping lipid peroxyl radical contributions to ROS-associated pathological processes in neurons.

Influences of Light Intensity and β-Carotene on Polycyclic Aromatic Hydrocarbons and Aldehydes in Vegetable Oil: A Case Study Using Palm Oil

This study investigated the effects of three light intensities on four types of palm oils during consecutive storage for 12 months at 4 °C. The concentrations of 4-hydroxy-2- trans-hexenal (4-HHE), 4-hydroxy-2- trans-nonenal (4-HNE), polycyclic aromatic hydrocarbon (PAH)4, and PAH8 in the oils significantly increased with the increasing light intensity after storage. The red palm oil had the lowest rate of increase of 4-HNE, while 5° palm oil had the highest rate of increase of the PAH, OPAH, 4-HNE, and peroxide values during storage. For the same type of oil, OPAHs increased significantly under a light intensity of 6000 lx (lx) after storage. The increasing concentrations of 9FO, ATQ, and BaPO in the oils stored at 6000 lx showed a positive relation to their corresponding parent PAHs, indicating that PAH oxidation occurred at 6000 lx. The results suggest that light intensity and β-carotene may control PAHs, OPAHs, and 4-hydroxy-trans- alkenals for vegetable oil storage, transportation, and retail.

Structural and functional changes in RNAse A originating from tyrosine and histidine cross-linking and oxidation induced by singlet oxygen and peroxyl radicals

Oxidation can be induced by multiple processes in biological samples, with proteins being important targets due to their high abundance and reactivity. Oxidant reactions with proteins are not comprehensively understood, but it is known that structural and functional changes may be a cause, or a consequence, of disease. The mechanisms of oxidation of the model protein RNAse A by singlet oxygen (¹O₂) were examined and compared to peroxyl radical (ROO^•) oxidation, both common biological oxidants. This protein is a prototypic member of the RNAse family that exhibits antiviral activity by cleaving single-stranded RNA. RNAse A lacks tryptophan and cysteine residues which are major oxidant targets, but contains multiple histidine, tyrosine and methionine residues; these were therefore hypothesized to be the major sites of damage. ¹O₂ and ROO^• induce different patterns and extents of damage; both induce cross-links and side-chain oxidation, and ¹O₂ exposure modulates enzymatic activity. Multiple products have been characterized including methionine sulfoxide and sulfone, alcohols, DOPA, 2-oxohistidine, histidine-derived ring-opened species and inter- and intra-molecular cross-links (di-tyrosine, histidine-lysine, histidine-arginine, tyrosine-lysine). In addition to methionine modification, which appears not to be causative to activity loss, singlet oxygen also induces alteration to specific histidine, tyrosine and proline residues, including modification and cross-linking of the active site histidine, His12. The high homology among the RNAse family suggests that similar modifications may occur in humans, and be associated with the increased risk of viral infections in people with diabetes, as markers for ¹O₂ have been found in early stages of this pathology.

Identification of urate hydroperoxide in neutrophils: A novel pro-oxidant generated in inflammatory conditions

Uric acid is the final product of purine metabolism in humans and is considered to be quantitatively the main antioxidant in plasma. In vitro studies showed that the oxidation of uric acid by peroxidases, in presence of superoxide, generates urate free radical and urate hydroperoxide. Urate hydroperoxide is a strong oxidant and might be a relevant intermediate in inflammatory conditions. However, the identification of urate hydroperoxide in cells and biological samples has been a challenge due to its high reactivity. By using mass spectrometry, we undoubtedly demonstrated the formation of urate hydroperoxide and its corresponding alcohol, hydroxyisourate during the respiratory burst in peripheral blood neutrophils and in human leukemic cells differentiated in neutrophils (dHL-60). The respiratory burst was induced by phorbol myristate acetate (PMA) and greatly increased oxygen consumption and superoxide production. Both oxygen consumption and superoxide production were further augmented by incubation with uric acid. Conversely, uric acid significantly decreased the levels of HOCl, probably because of the competition with chloride by the catalysis of myeloperoxidase. In spite of the decrease in HOCl, the overall oxidative status, measured by GSH/GSSG ratio, was augmented in the presence of uric acid. In summary, the present results support the formation of urate hydroperoxide, a novel oxidant in neutrophils oxidative burst. Urate hydroperoxide is a strong oxidant and alters the redox balance toward a pro-oxidative environment. The production of urate hydroperoxide in inflammatory conditions could explain, at least in part, the harmful effect associated to uric acid.

Effect of Glutathione Dehydrogenase of Lactobacillus sanfranciscensis on Gluten Properties and Bread Volume in Type I Wheat Sourdough Bread

Disulfide exchange reactions in wheat dough impact the polymerization of gluten and the volume of bread. In wheat sourdoughs fermented with Lactobacillus sanfranciscensis, glutathione reductase activity accumulates thiols. This study investigated the role of glutathione reductase and NADH oxidase of L. sanfranciscensis on disulfide exchange reactions, peroxide levels, and gluten polymerization in type I wheat sourdoughs. Fermentation with L. sanfranciscensis DSM20451 Δ gshR lacking glutathione reductase activity reduced the thiol levels in dough when compared to the wild type strain L. sanfranciscensis DSM20451. Fermentation with any strain reduced peroxides in wheat doughs when compared to a chemically acidified control. The impact of baker's yeast on thiol and peroxide levels was greater than the impact of lactobacilli. The depolymerization of gluten proteins was dependent on the free thiol content and dough acidification. Bread produced with the glutathione reductase deficient mutant strain had the highest specific volume compared with all the other groups.

Physiological analysis of the effect of altitudinal gradients on Leymus secalinus on the Qinghai-Tibetan Plateau

On the Qinghai-Tibetan Plateau, the high-altitudinal gradients can negatively affect plant distribution and limit plant growth and reproduction. Leymus secalinus (Georgi) Tzvel. is an important forage crop on the Qinghai-Tibetan Plateau and has an excellent ability to fix sand and improve soil. To evaluate the effect of altitude on the physiological characteristics of L. secalinus on the Qinghai-Tibetan Plateau, we measured the lipid peroxidation; chlorophyll a (Chl a), chlorophyll b (Chl b), total carotenoid (Car), soluble protein, proline and soluble sugar contents; and the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in leaves from eight different altitudes in Minhe County and Huangzhong County. The leaves were collected at the initial bloom stage, and the average vertical distance between two adjacent collection sites was approximately 100 meters. The reduction in Chl a and Chl b contents and the increase in Car contents can allow plants to weaken their light absorption and avoid photodamage to the chloroplast. The decrease in malondialdehyde (MDA) content associated with lower lipid peroxidation, and the changes of CAT, SOD and POD activities reflect a higher reactive oxygen species (ROS) scavenging capacity in high-altitude plants. The increase in proline and soluble sugar contents with elevation suggests that proline and soluble sugar may play a key role in the osmotic adjustment of plants in alpine regions. The results suggested that altitudinal gradients negatively affect L. secalinus on the Qinghai-Tibetan Plateau and that the adaptation mechanism and survival strategies of L. secalinus were attributed to the combined effects of multiple protective strategies.

Testing biomarker feasibility: a case study of Laeonereis culveri (Nereididae, Annelida) exposed to sewage contamination in a subtropical estuary

The feasibility of biomarkers to accurately detect pollution in estuaries and coastal areas appears to be overestimated in the scientific literature, and is likely stemming from a bias towards publishing only positive results. Herein, we test the applicability of antioxidant capacity and lipid peroxidation to detect potential in situ sewage impacts on a subtropical estuary. We experimentally assessed variation in malondialdehyde (MDA, an indicator of lipid peroxidation) and total antioxidant capacity against peroxyl radicals (ACAP) through transplantations of the worm Laeonereis culveri from control to sewage-polluted areas. Variations in biomarkers were more related to natural environmental variability and small-scale heterogeneity among areas than to experimental exposure to sewage. Use of oxidative stress biomarkers is promising but further experimental work under real-life conditions is necessary to further validate and establish their accuracy and feasibility for practical purposes.

Novofumigatonin biosynthesis involves a non-heme iron-dependent endoperoxide isomerase for orthoester formation

Novofumigatonin (1), isolated from the fungus Aspergillus novofumigatus, is a heavily oxygenated meroterpenoid containing a unique orthoester moiety. Despite the wide distribution of orthoesters in nature and their biological importance, little is known about the biogenesis of orthoesters. Here we show the elucidation of the biosynthetic pathway of 1 and the identification of key enzymes for the orthoester formation by a series of CRISPR-Cas9-based gene-deletion experiments and in vivo and in vitro reconstitutions of the biosynthesis. The novofumigatonin pathway involves endoperoxy compounds as key precursors for the orthoester synthesis, in which the Fe(II)/α-ketoglutarate-dependent enzyme NvfI performs the endoperoxidation. NvfE, the enzyme catalyzing the orthoester synthesis, is an Fe(II)-dependent, but cosubstrate-free, endoperoxide isomerase, despite the fact that NvfE shares sequence homology with the known Fe(II)/α-ketoglutarate-dependent dioxygenases. NvfE thus belongs to a class of enzymes that gained an isomerase activity by losing the α-ketoglutarate-binding ability.