Bimetallic iron-copper nanozyme for determination and degradation of norfloxacin in foods

Iron-copper nanozymes (Fe-Cu NZs) with good peroxidase activity were prepared through hydrothermal method by using copper nitrate as copper source, iron acetate as iron source and 2, 5-dihydroxyterephthalic acid as organic ligand. Upon oxidation of the colourless TMB to light blue products by Fe-Cu NZs, the addition of Norfloxacin (NOR) resulted in a colour change to dark blue. The absorbance of the system correlated linearly with NOR concentration in the range of 3.3 μM to 66 μM, and the detection limit (LOD) was 0.386 μM. A rapid colourimetric assay for the determination of NOR in food matrices was developed, with a detection time of only one minute. Additionally, the assay facilitated the simultaneous catalytic degradation of NOR via Fe-Cu NZs. The primary degradation mechanism of NOR was identified as the transformation of the quinolone ring and the cleavage of the C9 = C10 double bond, which was substantiated by high-performance liquid chromatography (HPLC).

A novel electrochemical strategy to detect hydrogen peroxide by utilizing peroxidase-mimicking activity of cerium oxide/graphene oxide nanocomposites

We herein describe a novel electrochemical strategy to detect hydrogen peroxide (H2O2) by utilizing the peroxidase-mimicking activity of cerium oxide nanoparticles (CeO2 NP) and reduced graphene oxide (rGO). Particularly, CeO2 NP/rGO nanocomposites were deposited on the commercial electrode by a very convenient and direct electrochemical reduction of graphene oxide. Due to the peroxidase-mimicking activity of CeO2 NP and the outstanding electrochemical properties of reduced graphene oxide, the reduction current of H2O2 was greatly enhanced. Based on this strategy, we reliably determined H2O2 down to 1.67 μM with excellent specificity and further validated its practical capabilities by robustly detecting H2O2 present in heterogeneous human serum samples. We believe that this work could serve as a new facile platform for H2O2 detection.

Determination of low concentrations of glucose through colorimetric analysis using CoFe2O4 magnetic catalyst and SAT-3

Natural enzyme mimics have attracted attention as alternatives to natural peroxidases. Among these, magnetic nanoparticles, especially ferrites, have attracted attention because of their unique electronic and physical structures, which are expected to be applied in various fields, including high-frequency magnetic materials, biomaterials, gas sensors, and semiconductor photocatalysts. The structural properties of the synthesized catalysts were investigated using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The prepared CoFe2O4 exhibited a spinel ferrite structure and formed a wood-flake-like bulk structure. In this study, magnetic CoFe2O4 was prepared using a precipitation method as a natural enzyme mimetic. CoFe2O4 showed excellent peroxidase-like activity, as demonstrated by the Michaelis-Menten constant (Km) and the maximum velocity (Vmax). The linear ranges of the calibration curves for H2O2 and glucose were in the range of 0-500 µM, and the detection limits were 1.83 and 5.91 µM, respectively. This analytical method was applied for the determination of glucose in human serum, and the results were satisfactory and consistent with certified values. The performance of this sensor was comparable to or superior to those of several other sensors commonly used for glucose analysis, indicating that its practical application is feasible.

Effect of proline content and histidine ligation on the dynamics of Ω-loop D and the peroxidase activity of iso-1-cytochrome c

To study how proline residues affect the dynamics of Ω-loop D (residues 70 to 85) of cytochrome c, we prepared G83P and G83A variants of yeast iso-1-cytochrome c (iso-1-Cytc) in the presence and absence of a K73H mutation. Ω-loop D is important in controlling both the electron transfer function of Cytc and the peroxidase activity of Cytc used in apoptosis because it provides the Met80 heme ligand. The G83P and G83A mutations have no effect on the global stability of iso-1-Cytc in presence or absence of the K73H mutation. However, both mutations destabilize the His73-mediated alkaline conformer relative to the native state. pH jump stopped-flow experiments show that the dynamics of the His73-mediated alkaline transition are significantly enhanced by the G83P mutation. Gated electron transfer studies show that the enhanced dynamics result from an increased rate of return to the native state, whereas the rate of loss of Met80 ligation is unchanged by the G83P mutation. Thus, the G83P substitution does not stiffen the conformation of the native state. Because bis-His heme ligation occurs when Cytc binds to cardiolipin-containing membranes, we studied the effect of His73 ligation on the peroxidase activity of Cytc, which acts as an early signal in apoptosis by causing oxygenation of cardiolipin. We find that the His73 alkaline conformer suppresses the peroxidase activity of Cytc. Thus, the bis-His ligated state of Cytc formed upon binding to cardiolipin is a negative effector for the peroxidase activity of Cytc early in apoptosis.

Guanosine-driven hyaluronic acid-based supramolecular hydrogels with peroxidase-like activity for chronic diabetic wound treatment

Guanosine is often used to construct supramolecular hydrogels due to its self-assembly properties, however, the high temperature and strong alkaline construction methods greatly limit its application in biomedical fields. In this work, a guanosine-driven hyaluronic acid-based supramolecular hydrogel was developed under mild condition by employing phenylboronic acid-functionalized hyaluronic acid (HA-PBA) backbone and guanosine molecules. Guanosines self-assembled into G-quartet planes under potassium ion conditions, and formed boronic ester bonds with HA-PBA, which induced rapid formation of dynamically cross-linked hydrogels. Hemin was then binding to the G-quartet plane via π-π interactions in the hydrogels, which exhibited peroxidase activity and were highly effective in killing bacteria by generating hydroxyl radicals in the presence of H2O2. Furthermore, glucose oxidase (GOx) was incorporated into the hydrogels and the HP/G@hemin@GOx hydrogels showed good antibacterial properties, modulation of wound glucose and ROS level, and good therapeutic efficacy for diabetic chronic wounds. Overall, the self-assembly of guanosine has been shown for the first time to be a feasible method for constructing natural polymer-based supramolecular hydrogels. This guanosine-driven HA-based supramolecular hydrogel can act as a potential wound dressing for chronic diabetic wound treatment. STATEMENT OF SIGNIFICANCE: Chronic wound repair remains an unsolved clinical challenge. Herein, we propose to utilize phenylboronic acid-modified hyaluronic acid and guanosine to construct supramolecular gels with peroxidase activity for chronic wound treatment. The self-assembly behavior of guanosine drives the natural macromolecular backbone to form the hydrogel, and the proposed method simplifies the gelation conditions and improves its biosafety. The G-quartets formed by the self-assembly of guanosine can act as the loading site for hemin. G-quartet/hemin complex imported peroxidase activity to the hydrogels, endowing them with the ability to kill bacteria and regulate ROS levels of cells in the wound site. This guanosine-driven supramolecular hydrogel significantly increased the rate of wound healing in diabetic mice, promising a new strategy for chronic wound treatment.

Molecular cloning and functional characterization of peroxinectin from red swamp crayfish, Procambarus clarkii

Peroxinectin, which has both peroxidase and cell adhesion activities, is crucial for invertebrate innate immune responses. In this study, we first cloned the full-length cDNA of Procambarus clarkii Peroxinectin (denoted as Pc-Px) and evaluated its immune roles. The Pc-Px cDNA had 2460 base pairs (bp) and 819 amino acid residues, including peroxidase domain and a putative integrin-binding motif. Pc-Px tissue expression was found to be ubiquitous in all examined tissues under normal physiological conditions. Pc-Px mRNA levels were highest in hemocytes, followed by gills and heart, and were lowest in the gut. The LPS, PGN, and Poly I:C treatment significantly up-regulated the transcript level of Pc-Px gene, but the expression trends were different after the microbials component treatments. Pc-Px knockdown using double-stranded RNA altered the transcription profiles of various immune-related genes in hepatopancreas of P. clarkii. Taken together, Pc-Px is an important component of immune system that likely to modulate immune function of P. clarkii via regulating immune-associated genes.

Peroxidase activity of rice (Oryza sativa) hemoglobin: distinct role of tyrosines 112 and 151

Five non-symbiotic hemoglobins (nsHb) have been identified in rice (Oryza sativa). Previous studies have shown that stress conditions can induce their overexpression, but the role of those globins is still unclear. To better understand the functions of nsHb, the reactivity of rice Hb1 toward hydrogen peroxide (H2O2) has been studied in vitro. Our results show that recombinant rice Hb1 dimerizes through dityrosine cross-links in the presence of H2O2. By site-directed mutagenesis, we suggest that tyrosine 112 located in the FG loop is involved in this dimerization. Interestingly, this residue is not conserved in the sequence of the five rice non-symbiotic hemoglobins. Stopped-flow spectrophotometric experiments have been performed to measure the catalytic constants of rice Hb and its variants using the oxidation of guaiacol. We have shown that Tyrosine112 is a residue that enhances the peroxidase activity of rice Hb1, since its replacement by an alananine leads to a decrease of guaiacol oxidation. In contrast, tyrosine 151, a conserved residue which is buried inside the heme pocket, reduces the protein reactivity. Indeed, the variant Tyr151Ala exhibits a higher peroxidase activity than the wild type. Interestingly, this residue affects the heme coordination and the replacement of the tyrosine by an alanine leads to the loss of the distal ligand. Therefore, even if the amino acid at position 151 does not participate to the formation of the dimer, this residue modulates the peroxidase activity and plays a role in the hexacoordinated state of the heme.

Heme-Aβ in SDS micellar environment: Active site environment and reactivity

Alzheimer's disease (AD), the most common cause of dementia, is a progressive neurodegenerative disorder that causes brain cell death. Oxidative stress derived from the accumulation of redox cofactors like heme in amyloid plaques originating from amyloid β (Aβ) peptides has been implicated in the pathogenesis of AD. In the past our group has studied the interactions and reactivities of heme with soluble oligomeric and aggregated forms of Aβ. In this manuscript we report the interaction of heme with Aβ that remains membrane bound using membrane mimetic SDS (sodium dodecyl sulfate) micellar medium. Employing different spectroscopic techniques viz. circular dichroism (CD), absorption (UV-Vis), electron paramagnetic resonance (EPR) and resonance Raman (rR) we find that Aβ binds heme using one of its three His (preferentially His13) in SDS micellar medium. We also find that Arg5 is an essential distal residue responsible for higher peroxidase activity of heme bound Aβ in this membrane mimetic environment than free heme. This peroxidase activity exerted by even membrane bound heme-Aβ can potentially be more detrimental as the active site remains close to membranes and can hence oxidise the lipid bilayer of the neuronal cell, which can induce cell apoptosis. Thus, heme-Aβ in solution as well as in membrane-bound form are detrimental.

Effects of naturally occurring S47F/A mutations on the structure and function of human cytochrome c

The sequence and structure of human cytochrome c (hCyt c) exhibit evolutionary conservations, with only a limited number of naturally occurring mutations in humans. Herein, we investigated the effects of the naturally occurring S47F/A mutations on the structure and function of hCyt c in the oxidized form. Although the naturally occurring S47F/A mutations did not largely alter the protein structure, the S47F and S47A variants exhibited a small fraction of high-spin species. Kinetic studies showed that the peroxidase activity of the variants was enhanced by ∼2.5-fold under neutral pH conditions, as well as for the rate in reaction with H₂O₂, when compared to those of wild-type hCyt c. In addition, we evaluated the interaction between hCyt c and human neuroglobin (hNgb) by isothermal titration calorimetry (ITC) studies, which revealed that the binding constant was reduced by ∼8-fold as result of the mutation of the hydrophilic Ser to the hydrophobic Phe/Ala. These findings provide valuable insights into the role of Ser47 in Ω-loop C in sustaining the structure and function of hCyt c.

Ag+-gated peroxidase activity of gold nanoparticles for sensitive detection of Escherichia coli

Escherichia coli (E. coli) is one of the most ubiquitous foodborne pathogens that can cause infections and threaten human health. Herein, a colorimetric method for sensitive detection of E. coli was established by using enzyme-nanozyme cascade reaction for signal amplification. Gold nanoparticles (AuNPs) are well-known nanozymes due to their high peroxidase-like activity. When the dense cetyltrimethylammonium bromide (CTAB) membrane on the surfaces of AuNPs kept the substrate away from AuNPs, the peroxidase activity of AuNPs was inhibited. However, the CTAB membrane could be disrupted by Ag⁺, resulting in enhanced peroxidase activity of AuNPs. When E. coli was present, the enzyme-nanozyme cascade reaction was initiated. The substrate p-aminophenyl β-D-galactopyranoside (PAPG) was hydrolyzed to the reductive p-aminophenol (PAP) by beta-galactosidase (β-gal) in E. coli, reducing Ag⁺ to Ag. Consequently, CTAB-AuNPs remained weak peroxidase activity and could not catalyze the H₂O₂-mediated oxidation of TMB. As the amount of E. coli increased, the absorbance of TMB decreased along with a color change from deep blue to pink. The absorbance intensity displayed a linear dependence on E. coli from 1.0 × 10² to 1.0 × 10⁹ CFU mL^-1. Therefore, the proposed method holds good prospects in foodborne pathogenic bacteria detection.

Parameters optimization of Fe3O4 NPs synthesis by Tamarindus indica leaf extract possessing both peroxidase as well as excellent dye removal activity

This study reports optimized conditions for the green synthesis of iron (II,III) oxide nanoparticles (Fe₃O₄ NPs) from Tamarindus indica (T. indica) leaf extract. The synthetic parameters like concentration of leaf extract, solvent system, buffer, electrolyte, pH, and time were optimized for Fe₃O₄ NPs synthesis. Fe₃O₄ NPs were obtained from the synthesis protocol by measuring size (80 ± 3 nm approx.), characteristics color changes, and an absorption peak between 270 nm and 280 nm using a UV-visible spectrophotometer, scanning electron microscope (SEM), and an energy dispersive X-ray spectrometer (EDS) study. Peroxidase activity was tested with 3,3,5,5-Tetramethylbenzidine (TMB) oxidation in the presence of hydrogen peroxide and dye removal activity was tested with malachite green (MG). The results indicated that the successful synthesis of Fe₃O₄ nanoparticles using aqueous leaf extract of T. indica is a practical alternative for biomedical applications due to its potent peroxidase activity and high dye removal capacity (about 93% with UV light and 55% with room light).

Conserved acidic second shell residue modulates the structure, stability and activity of non-seleno human peroxiredoxin 6

1-Cys peroxiredoxin6 (Prdx6) is unique and inducible bifunctional enzyme in the mammalian lungs and plays a role in the progression and inhibition of cancerous cells at different stages. The enzyme possesses two distinct active sites for phospholipase A2 and peroxidase activity. The conserved residues surrounding the peroxidase active site, also called as second shell residues are Glu50, Leu71, Ser72, His79 and Arg155. Since there is no study done about the active site stabilization of the transition state of Prdx6, there are a lot of questions unanswered regarding the Prdx6 peroxidase activity. In order to evaluate the role of second shell conserved residue Glu50, present in close vicinity to peroxidatic active site, we substituted this negatively charged residue with Alanine and Lysine. To explore the effect of mutation on the biophysical parameters, the mutant proteins were compared with Wild-Type by using biochemical, biophysical, and in silico methods. Comparative spectroscopic methods and enzyme activity demonstrate that the Glu50 plays a significant role in maintaining the structure, stability, and function of protein. From the results we conclude that Glu50 significantly controls the structure; stability and may be involved in the active site stabilization of transition state for proper position of diverse peroxides.

Enzymatic Properties of Red Beet (Beta vulgaris L.) Leaf, root Pulp, and peel

BACKGROUND

Beetroot (Beta vulgaris L.) is botanically classified as a herbaceous biennial belonging to the Chenopodiaceae family and has several varieties with bulb colors ranging from yellow to red. Peroxidases are widely occurring in organisms including microorganisms, plants, and animals, and have been involved in various physiological and biochemical functions.

OBJECTIVE

The study was conducted to investigate the characteristics of enzyme extracts from red beet leaves, root pulp, and peel.

METHODOLOGY

The enzyme extraction involved the homogenization of the sample and filtrate in cold acetone and then the filtrate was homogenized in 0.1M sodium acetate buffer, pH 7. The protein content was determined using the Lowry assay using bovine serum albumin (BSA) as a standard protein. Then, enzymatic activity was determined by peroxidase, polyphenol oxidase, and catalase assays. The antioxidant activities of the enzyme extract were conducted by using DPPH and hydrogen peroxide free radical scavenging activities.

RESULTS

The result indicated that the Enzymatic activity of crude enzyme extract of red beet leaf, root pulp and peel indicated that significantly the highest total soluble protein (16.68mg/ml), peroxidase activity (PODA, 111.50U/ml), polyphenol oxidase activity (PPOA, 170.90U/ml), polyphenol oxidase specific activity (PPOspa, 10.25U/mg), catalase activity (CATA, 180.50U/ml) and catalase specific activity (CATspa, 10.82U/mg), were recorded for red beet leaf enzyme extract. The antioxidant activity of the enzyme extracts demonstrated that significantly higher DPPH radical scavenging activity of leaf extract (59.16) and peel extract (61.92) were recorded. The Pearson correlation coefficient of enzyme activity parameters and free radical scavenging activities presented that protein content was significantly and positively correlated with CATA, PPOA, and PPOspa. Catalase-specific activity (CATspa) was significant and positively correlated only with HPSA. Peroxidase-specific activity (PODspa) was significant and positively correlated with PODA and DPPH. Based on the plot for principal component PC2 vs PC1 for D statistics DPPH, PODA, and PODspa have close PC1 and PC2 scores (with vector angle [90]^0) showing similar/correlated effects.

CONCLUSION

In this study, B. vulgaris has shown promising peroxidase enzyme activity. Beetroot peel contained higher antioxidant compounds thus promising a more intense utilization of the peels in food and nutraceuticals.

Ethylene positively regulates Cd tolerance via reactive oxygen species scavenging and apoplastic transport barrier formation in rice

Ethylene regulates plant root growth and resistance to environment stress. However, the role and mechanism of ethylene signaling in response to Cd stress in rice remains unclear. Here, we revealed that ethylene signaling plays a positive role in the resistance of rice to Cd toxicity. Blocking the ethylene signal facilitated root elongation under normal conditions, but resulted in severe oxidative damage and inhibition of root growth under Cd stress. Conversely, ethylene signal enhancement by EIN2 overexpression caused root bending, similar to the response of roots to Cd stress, and displayed higher Cd tolerance than the wildtype (WT) plants. Comparative transcriptome analysis indicated EIN2-mediated upregulation of genes involved in flavonoid biosynthesis and peroxidase activity under Cd stress. The synthesis of phenolic acids and flavonoids were positively regulated by ethylene. Thus, the ein2 (ethylene insensitive 2) mutants displayed lower ROS scavenging capacity than the WT. Moreover, a significant increase in Cd accumulation and relatively increased apoplastic flow were observed in the root apex of the ein2 mutant compared with the WT plants. Overall, EIN2-mediated Cd resistance in rice is mediated by the upregulation of flavonoid biosynthesis and peroxidase activity to induce ROS scavenging, and apoplastic transport barrier formation reduces Cd uptake.

Enhancement of Activity for Peroxidase-Mimicking DNAzyme by Covalent Attachment of Hemin to G-Quadruplex-Forming Oligonucleotide Using Click Chemistry

Peroxidase-mimicking DNAzymes are used in the development of new bioanalytical assays due to their advantages like thermal stability, simple synthesis and purification, and ability to hybridize with the complementary strand of nucleic acid. Here, we describe the method of covalent attachment of hemin to DNA oligonucleotide using click chemistry that allows good yield (60-70%) of the final conjugate product. The activity of obtained DNAzymes is monitored using chromogenic and fluorogenic substrates.

Molecular insights on the conformational dynamics of a P76C mutant of human cytochrome c and the enhancement on its peroxidase activity

In apoptotic pathway, the interaction of Cytochrome c (Cytc) with cardiolipin in vivo is a key process to induce peroxidase activity of Cytc and trigger the release of Cytc in the inner mitochondria into cytosol. The peroxidase active form of Cytc occurs due to local conformational changes that support the opening of the heme crevice and the loss of an axial ligand between Met80 and heme Fe. Structural adjustments at the Ω-loop segments of Cytc are required for such process. To study the role of the distal Ω-loop segments comprising residues 71-85 in human Cytc (hCytc), we investigated a cysteine mutation at Pro76, one of the highly conserved residues in this loop. The effect of P76C mutant was explored by the combination of experimental characterizations and molecular dynamics (MD) simulations. The peroxidase activity of the P76C mutant was found to be significantly increased by ∼13 folds relative to the wild type. Experimental data on global denaturation, alkaline transition, heme bleaching, and spin-labeling Electron Spin Resonance were in good agreement with the enhancement of peroxidase activity. The MD results of hCytc in the hexacoordinate form suggest the important changes in P76C mutant occurred due to the unfolding at the central Ω-loop (residues 40-57), and the weakening of H-bond between Tyr67 and Met80. Whereas the experimental data implied that the P76C mutant tend to be in equilibrium between the pentacoordinate and hexacoordinate forms, the MD and experimental information are complementary and were used to support the mechanisms of peroxidase active form of hCytc.

Neuroprotective effects of Withania somnifera in the SH-SY5Y Parkinson cell model

Parkinson's disease is the most frequent neurodegenerative motor disorder. The clinical syndrome and pathology involve motor disturbance and the degeneration of dopaminergic neurons in the substantia nigra. Root extracts of Withania. somnifera, commonly called Ashwagandha, contain several major chemical constituents known as withanolides. Studies have shown that W. somnifera extracts exhibit numerous therapeutic effects including inflammation and oxidative stress reduction, memory and cognitive function improvement. This study aimed to evaluate the protective effects of KSM-66, W. somnifera root extract, on 6-hydroxydopamine (6-OHDA)-induced toxicity in the human neuroblastoma SH-SY5Y cell line, as well as the associated oxidative response protein expression and redox regulation activity focused on S-glutathionylation. SH-SY5Y cells were treated with 6-OHDA preceded or followed by treatment with the KSM-66 extract. Using KSM-66 concentrations ranging from 0.25 to 1 mg/ml before and after treatment of the cells with 6-OHDA has resulted in an increased viability of SH-SY5Y cells. Interestingly, the extract significantly increased glutathione peroxidase activity and thioltransferase activity upon pre- or post- 6-OHDA treatment. KSM-66 also modulated oxidative response proteins: peroxiredoxin-I, VGF and vimentin proteins upon 6-OHDA pre/post treatments. In addition, the extract controlled redox regulation via S-glutathionylation. Pre-treatment of SH-SY5Y cells with KSM-66 decreased protein-glutathionylation levels in the cells treated with 6-OHDA. The rescue of mitochondria with 0.5 mg/ml KSM-66 extract showed an increase in ATP levels. These findings suggest that W. somnifera root extract acts as a neuroprotectant, thereby introducing a potential agent for the treatment or prevention of neurodegenerative diseases.

Tobacco hairy root's peroxidases are rhythmically controlled by phenol exposure

Plants like almost all living organisms, have developed a biological clock or circadian clock (CC) capable of synchronizing and adjusting various metabolic and physiological processes at certain times of the day and in a period of 24 h. This endogenous timekeeping is able to predict the environmental changes providing adaptive advantages against stressful conditions. Therefore, the aim of this work was to analyze the possible link between metabolism of xenobiotic compounds (MXC) and the CC. Synchronized Nicotiana tabacum hairy roots (HRs) were used as a validated plant model system, and peroxidases (PODs), key enzymes of the phase I in the MCX, were evaluated after phenol treatment. Two POD genes were selected and their temporal expression profiles as well as the total POD activity were analyzed in order to find circadian oscillations either under control conditions or phenol treatment. It was demonstrated that these PODs genes showed oscillatory profiles with an ultradian period (period length shorter than the circadian period), and preserving the same phases and expression peaks still under phenol treatment. The total PODs activity showed also a marked oscillatory behavior mainly in phenol-treated HRs with the highest levels at ZT23. Untreated HRs showed decrease and increase in the intensity of some basic isoforms at light and dark phase, respectively, while in phenol- treated HRs, an increase in the intensity of almost all isoforms was observed, mainly during the dark phase, being coincident with the high PODs activity detected at ZT23. The periodic analysis determined an ultradian period either in total POD activity or in the POD activity of isoform VI, being 18.7 and 15.3 h, respectively. Curiously, in phenol treated HRs, the period length of total POD activity was longer than in untreated HRs, suggesting that phenol could induce a marked oscillatory behavior in the POD activity with better performance during the dark phase, which explain the higher phenol removal efficiencies at ZT23. These findings showed novel information about the performance of PODs, which would be rhythmically controlled at biochemical level, by phenol exposure.

Molecular cloning and functional characterization of a thioredoxin peroxidase gene in Echinococcus multilocularis

Thioredoxin peroxidase (TPx) plays an important role in protecting parasites against oxidative damage. However, studies on the role of TPxs in Echinococcus multilocularis are limited. In this study, one tpx gene of E. multilocularis, named as emtpx-1, was identified. EmTPx-1 shares two positionally conserved cysteine residues (Cys48 and Cys169) with orthologs from other platyhelminths. EmTPx-1 is highly expressed in the germinal layer and present in exosome-like vesicles secreted by E. multilocularis metacestodes. EmTPx-1 displays peroxidase activity, which removes hydrogen peroxide in the presence of dithiothreitol. Furthermore, EmTPx-1 could protect DNA from oxidative damages, and EmTPx-1-expressing E. coli cells had an enhanced resistance to oxidative stress. In addition, EmTPx-1 enhanced the expression of arg1, ym1, and il-10, but suppressed inos, tnf-α, and il-1β expression in LPS-stimulated macrophages. Our data suggest a critical role for EmTPx-1 in oxidative stresses and M2 macrophage polarization.

Influence of cysteine-directed mutations at the Ω-loops on peroxidase activity of human cytochrome c

Cytochrome c (Cytc) is a multifunctional protein associated with electron shuttling in the inner membrane of mitochondria and also involving in the apoptotic pathway. It has been identified that mutations located in the flexible central 40-57 Ω-loop including the naturally occurring G41S, Y48H, and A51V mutants, which are found in patients with thrombocytopenia 4, a platelet disorder, alter the structural properties of human Cytc (hCytc) that associated to enhanced peroxidase activity. In this work we compared the cysteine-directed mutants of hCytc located in three different parts of Ω-loops, i.e., T28C and G34C (proximal Ω-loop), and A50C (central Ω-loop), with respect to the wild-type (WT) hCytc. The mutants and WT hCytc were structurally characterized by circular dichroism, heating and chemical denaturations, and fluorescence spectroscopy. The flexibility at the cysteine mutated sites was directly determined by site-directed spin-labeling Electron Spin Resonance. Alkaline transitions were determined by pH titration and the alkaline conformers were related to peroxidase activity of all hCytc proteins. Structural and dynamic characterizations were rationally correlated to the modulation of peroxidase activity in these mutants in comparison to the WT hCytc. We found that the cysteine mutations at residues T28 and G34, both located in the same region of Ω-loop, developed different conformations and dynamical properties that lead to different effects on the rates of peroxidase activity (G34C was ~2.6 folds higher), whereas the rate of G34C was closer to that of A50C mutant. The results implied that the flexibility and local structures of the proximal Ω-loop could also play an important role in modulating the peroxidase activity which can be associated to apoptosis.

Mechanism of reactivation of the peroxidase catalytic activity of human cyclooxygenases by reducing cosubstrate quercetin

Our earlier studies show that the peroxidase activity of cyclooxygenase 1 and 2 (COX-1 and COX-2) can be reactivated in vitro and in vivo by the presence of certain naturally-occurring flavonoids such as quercetin and myricetin, which serve as reducing cosubstrates. These compounds can activate COX at nanomolar concentrations. In the present study, quercetin is used as a representative model compound to investigate the chemical mechanism by which the peroxidase activity of human COX-1 and COX-2 is reactivated after each catalytic cycle. Molecular docking and quantum mechanics calculations are carried out to probe the interactions of quercetin with the peroxidase sites of COX-1/2 and the reactivation mechanism. It is found that some of the partially-ionized states of quercetin can bind tightly and closely inside the peroxidase active sites of the COX enzymes and directly interact with heme Fe ion. While quercetin contains several phenolic hydroxyl groups, it is found that only the C-3'-OH group can effectively donate an electron for the reduction of heme because it not only can bind closely and tightly inside the peroxidase sites of COX-1/2, but it can also facilely donate an electron to heme Fe ion. This investigation provides a mechanistic explanation for the chemical process by which quercetin reactivates COX-1/2 peroxidases. This knowledge would aid in the rational design of drugs that can selectively target the peroxidase sites of COX-1/2 either as activators or inhibitors.

Early sex determination of Ginkgo biloba based on the differences in the electrocatalytic performance of extracted peroxidase

Ginkgo biloba is a dioecious plant. Male ginkgoes are mainly used in landscaping, while females are mainly used for fruit production. However, sex identification of ginkgo is a difficult task, especially at the seedling stage. In this work, we present for the first time the use of electrochemical techniques for the identification of ginkgo sex based on the differences in peroxides within male and female ginkgos. Graphene was used to concentrate peroxides in ginkgo extract, thereby improving electrochemical signal sensitivity. The electrochemical reduction of hydrogen peroxide catalyzed by peroxidase was used as a prob for sex determination in ginkgo. This electrochemical identification technique can be used not only for the analysis of adult ginkgo, but also successfully for the analysis of tissue culture seedlings and live seedlings. This electrochemical sensor has excellent discrimination ability due to the difference in peroxidase content in the leaves and petiole of ginkgo of different sexes. This electrochemical sensor allows for a rapid identification of the sex of ginkgo and has a very strong potential for field analysis.

The effects of exogenous application of melatonin on the degradation of polycyclic aromatic hydrocarbons in the rhizosphere of Festuca

The study aimed to assess the effects of melatonin, a plant growth regulator, on the degradation of phenanthrene (Phe) and pyrene (Py), in the rhizosphere of the Festuca grass. The experiments were divided into the following groups: 1) soil contaminated with Phe and Py, without the Festuca, 2) contaminated soil + Festuca, 3-5), contaminated soil + Festuca + the application of melatonin in three separate doses: 10, 50, or 100 μM. After 90 days, the effects of melatonin supplementation on the degradation of polycyclic aromatic hydrocarbons (PAHs) were analyzed by evaluating the rate of PAHs degradation, the expression of genes encoding salicylaldehyde dehydrogenase (SDH) and glutathione peroxidase (GPX) enzymes in Pseudomonas putida, as well as by measuring the total activity of dehydrogenase and peroxidase enzymes. Our results have shown that in soil contaminated by 300 mg kg^-1 PAHs, application of melatonin (10, 50, 100 μM), resulted in the following increase in the dehydrogenase and peroxidase activity in all three applied doses (19% and 5.7%), (45.3% and 34.3%), (40.9% and 14.3%), respectively in comparison to the control group. The experiment showed that soil supplementation with melatonin at 50 μM, resulted in the highest removal rate of PAHs. According to our results, melatonin demonstrated a potentially favorable role in enhancing plant biomass, as well as an increase in soil bacterial population, and the activity of antioxidative enzymes in P. putida, causing all tested parameters of the soil and the expression of desired genes to be advantageously altered for the degradation of the chosen PAHs.

Lysine 72 substitutions differently affect lipid membrane permeabilizing and proapoptotic activities of horse heart cytochrome c

Peroxidase activity of cytochrome c (cyt c)/cardiolipin (CL) complex is supposed to be involved in the initiation of apoptosis via peroxidative induction of mitochondrial membrane permeabilization. As cyt c binding to CL-containing membranes is at least partially associated with electrostatic protein/lipid interaction, we screened single-point mutants of horse heart cyt c with various substitutions of lysine at position 72, considered to play a significant role in both the binding and peroxidase activity of the protein. Contrary to expectations, K72A, K72R and K72L substitutions exerted slight effects on both the cyt c binding to CL-containing liposomal membranes and the cyt c/H₂O₂-induced calcein leakage from liposomes, used here as a membrane permeabilization assay. Both the binding and permeabilization were decreased to various extents, but not significantly, in the case of K72E and K72N mutants. A drastic difference was found between the sequence of the permeabilizing activities of the cyt c variants and the previously described order of their proapoptotic activities (Chertkova et al., 2008).

Rapid in-situ growth of gold nanoparticles on cationic cellulose nanofibrils: Recyclable nanozyme for the colorimetric glucose detection

Novel microwave-assisted green in-situ synthesis of positively charged gold nanoparticles (AuNPs) supported by cationic cellulose nanofibrils (C.CNF) within 30 s and devoid of additional reducing agent is reported. Peroxidase activity of these positive AuNPs was studied and that appeared to be superior over its negative charged counterpart. Further the AuNPs@C.CNF is casted into a film which makes it reusable. Using TMB substrate, simple and sensitive colorimetric detection methods for H₂O₂ and glucose were established. Under optimal conditions, the linear ranges were found to be 0.5-30 μM and 1-60 μM, and the detection limits were 0.30 and 0.67 μM for H₂O₂ and glucose, respectively. The film was potentially reused for the detection of glucose up to five cycles without a decrease in the activity. Further, this technique was employed to quantify glucose in human serum samples, and the obtained results were comparable with those of the standard GOD-POD method.

Structural and functional characterization of complexes between heme and dimeric parallel G-quadruplex DNAs

Heme has been receiving considerable interest as a prosthetic group of ribozymes and deoxyribozymes, because heme-bound nucleic acids exhibit peroxidase-like catalytic activities (Travascio, P., Li, Y., and Sen, D. (1998) Chem. Biol, 5, 505-517). The interaction of heme with dimeric G-quadruplexes formed from d(TAGGGTTAGGGT) and d(TAGGGTTAGGGA) has been characterized to gain a deeper understanding of the molecular recognition of G-quadruplex DNAs by heme. We found that heme binds selectively to the 3'-terminal G-quartet of a dimeric parallel G-quadruplex of d(TAGGGTTAGGGT), whereas binding of heme to a dimeric antiparallel G-quadruplex of d(TAGGGTTAGGGA) does not occur, suggesting that an orderly arrangement of the constituent guanine deoxyribose rings, with respect to the G-quartet plane, is crucial for the binding of heme to the DNA. The preferential binding of heme to the 3'-terminal G-quartet of parallel G-quadruplex DNAs allowed a systematic modification of the heme environment in the complex through the DNA sequence. The activity of the complexes was found to increase with increasing number of adenine bases adjacent to the heme in the complexes, possibly due to improvement of the accessibility of aromatic substrate, i.e., 10-acetyl-3,7-dihydroxyphenoxazine, to the heme, and an increase in the frequency of appearance of a specific orientation of the adenine bases, with respect to the heme, optimized for its activity as an acid-base catalyst to enhance the peroxidase activity of the complex.

Hemoglobins from Scapharca subcrenata (Bivalvia: Arcidae) likely play an bactericidal role through their peroxidase activity

Hemoglobin (Hb) is an iron-containing respiratory protein present in all vertebrates and some invertebrates. The blood clam Scapharca subcrenata is one of the few invertebrates that have Hb-containing red hemocytes. In this study, we purified Hb (Ss-Hb), including Ss-HbI and Ss-HbII, from S. subcrenata hemocytes using gel chromatography with a recovery rate of 70.71%, and then characterized their peroxidase activities. Both Ss-Hbs possessed peroxidase activity with high affinity to the substrates guaiacol and H₂O₂. Moreover, both Ss-Hbs had structural similarities, such as type b heme, proximal histidine (His), distal His, and heme pocket arginine (Arg), with other peroxidases. The optimal peroxidase activity of both Ss-Hbs was at pH 5 and 35 °C, but this was inhibited in the presence of Cu²⁺ and Fe²⁺. Ss-Hbs produced [Formula: see text] in the presence of H₂O₂. β-phenylethylamine, a substrate of peroxidase, increased the [Formula: see text] generation, while Cu²⁺, an inhibitor of peroxidase, inhibited this reaction. These results indicated that the peroxidase cycle of Ss-Hb was involved in the production of [Formula: see text] . A large amount of [Formula: see text] may be generated by the peroxidase cycle if the substrate is sufficient. During the incubation of Ss-Hbs with Bacillus subtilis, it was speculated that trace H₂O₂, probably from autoxidation of Ss-Hbs or generated by B. subtilis, started the peroxidase cycle of Ss-Hb. and produced a large amount of [Formula: see text] in the presence of sufficient substrate in the culture medium. It is therefore reasonable to assume that Ss-Hbs played an antibacterial role owing to their peroxidase activity, which produced [Formula: see text] .

Modulating the biological function of protein by tailoring the adsorption orientation on nanoparticles

Protein orientation in nanoparticle-protein conjugates plays a crucial role in binding to cell receptors and ultimately, defines their targeting efficiency. Therefore, understanding fundamental aspects of the role of protein orientation upon adsorption on the surface of nanoparticles (NPs) is vital for the development of clinically important protein-based nanomedicines. In this work, new insights on the effect of the different orientation of cytochrome c (cyt c) bound to gold nanoparticles (GNPs) using various ligands on its apoptotic activity is reported. Time-of-Flight Secondary-Ion Mass Spectrometry (ToF-SIMS), electrochemical and circular dichroism (CD) analyses are used to investigate the characteristics of cyt c orientation and structure on functionalized GNPs. These studies indicate that the orientation and position of the heme ring inside the cyt c structure can be altered by changing the surface chemistry on the GNPs. A difference in the apoptosis inducing capability because of different orientation of cyt c bound to the GNPs is observed. These findings indicate that the biological activity of a protein can be modulated on the surface of NPs by varying its adsorption orientation. This study will impact on the rational design of new nanoscale biosensors, bioelectronics, and nanoparticle-protein based drugs.

Comparative transcriptome analysis of Tilletia horrida infection in resistant and susceptible rice (Oryza sativa L.) male sterile lines reveals potential candidate genes and resistance mechanisms

Rice kernel smut (RKS), caused by the basidiomycete fungus Tilletia horrida, is one of the most devastating diseases affecting the production of male sterile lines of rice (Oryza sativa) worldwide. However, the molecular mechanisms of resistance to T. horrida have not yet been explored. In the present study, RNA sequencing analysis of rice male sterile lines, that are resistant and susceptible to RKS (Jiangcheng 3A and 9311A, respectively) was conducted after T. horrida infection. Transcriptomic analysis showed that a greater number of differentially expressed gene (DEGs) was observed in Jiangcheng 3A compared with 9311A after T. horrida inoculation. Furthermore, 4, 425 DEGs were uniquely detected in Jiangcheng 3A, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of these DEGs revealed that oxidoreductase activity, peroxidase activity, cutin, suberine and wax biosynthesis, and flavonoid biosynthesis were key pathways for T. horrida resistance. In summary and based on transcriptome analysis, we suggest a preliminary regulatory mechanism for Jiangcheng 3A cultivar resistance response to T. horrida inoculation.

Catalase active metal-organic framework synthesized by ligand regulation for the dual detection of glucose and cysteine

Mimic enzymes greatly improve the inherent insufficiencies of natural enzymes. Therefore, mimic enzyme sensors attract increasing research interest. Metal-organic framework (MOF) is emerging in the field of mimic enzyme catalysis due to its remarkable structural properties. In this paper, a colorimetric method is designed for rapid and sensitive detection of glucose and cysteine levels. The MOF Eu-pydc (pydc-2,5-pyridinedicarboxylic acid) is synthesized by a new strategy which is regulated by ligands at room temperature and found to have peroxidase activity. Then, the MOF is used as a mimic enzyme to catalyze chromogenic substrate (3,3',5,5'-tetramethylbenzidine, TMB) for colorimetric sensing of glucose. The developed method can accurately detect glucose in the range of 10 μM-1 mM (R² = 0.9958) with a relatively low detection limit about 6.9 μM. Moreover, a cysteine sensor with a detection limit of 0.28 μM is also established based on the disappearance of the color of oxTMB. Additionally, the proposed glucose sensor exhibits excellent selectivity and is successfully applied to blood glucose detection. At the same time, the detection of cysteine is also highly sensitive. In short, the dual sensor is fast, low cost, and convenient, and has great application potential in the diagnosis of disease.

Synthesis of cost-effective magnetic nano-biocomposites mimicking peroxidase activity for remediation of dyes

The present study describes preparation of cellulose incorporated magnetic nano-biocomposites (CNPs) by using cellulose as base material. The prepared CNPs were characterised by SEM, EDAX, TEM, XRD, and FT-IR and found to exhibit an intrinsic peroxidase-like activity with a K_m and V_max of 550 μM and 3.8 μM/ml/min, respectively. The CNPs exhibited higher pH and thermal stability compared to commercial peroxidase. These nanocomposites were able to completely remove (i) a persistent azo dye, methyl orange at a concentration of 50 ppm, within 60 min under acidic conditions (pH 3.0) and also (ii) decolourize commercial textile dye mixture under acidic conditions within 30 min. CNP-mediated degradation of dyes into simple products was further confirmed by UV-Vis and AT-IR spectroscopy The added advantage of CNPs separation after decolourization by simple magnet due to their magnetic properties and consequent reusability makes them fairy attractive system for dye remediation from environmental samples or textile industries effluents.

Electron microscopy cytochemistry and three-dimensional reconstruction of labeled structures in Trypanosoma cruzi

Significant advances have occurred in the area of high-resolution scanning electron microscopy (SEM), especially related to methodologies that allow the observation of intracellular structures that are exposed either by successive abrasion with a gallium ion beam or by sectioning in epoxy-embedded cells. Images of series of successively exposed surfaces can then be rendered into 3D models. Here, we report our observations by combining this approach with classical cytochemical methods to facilitate the 3D reconstruction of labeled structures and organelles. We used epimastigotes of Trypanosoma cruzi whose endocytic pathway was labeled with horseradish peroxidase, followed by fixation and detection of the peroxidase activity using the classical diaminobenzidine-osmium method followed by incubation with thiocarbohydrazide, which increases the concentration of osmium at the sites where the enzyme is located as well as the contrast of lipid-containing structures. This procedure allows not only a better visualization of membranous structures and lipid inclusions but can also easily identify the endocytic tracer (HRP) inside the cell. All structures involved in the endocytic activity could be traced and reconstructed.

Electronic coupling between molybdenum disulfide and gold nanoparticles to enhance the peroxidase activity for the colorimetric immunoassays of hydrogen peroxide and cancer cells

Peroxidase nanoenzymes exhibit a specific affinity toward substrates, thereby demonstrating application potential for realizing the colorimetric immunoassays of hydrogen peroxide (H₂O₂), which can be further used as a probe for imaging cancer cells. To enhance the intrinsic peroxidase activity of molybdenum sulfide (MoS₂) nanomaterials, gold (Au) nanoparticles with an average diameter of approximately 2.1 nm were modified on a MoS₂/carbon surface (denoted as MoS₂/C-Au₆₀₀) via ascorbic acid reduction. MoS₂/C-Au₆₀₀ can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to generate a blue oxidation product in the presence of H₂O₂; this product exhibits peroxidase-like activities, superior to those of most existing MoS₂-based nanoenzymes. Furthermore, MoS₂/C-Au₆₀₀ exhibits a high detection capability for H₂O₂ in the range of 1 × 10^-5 to 2 × 10^-4 mol/L (R² = 0.99), and the lowest detection limit is 1.82 µmol/L in a sodium acetate and acetic acid buffer solution. Steady state kinetics studies indicate that the catalytic mechanism is consistent with the ping-pong mechanism. Given its strong absorption peak at 652 nm in the visible region, MoS₂/C-Au₆₀₀ can be used to image cancer cells due to the enhanced permeability and retention effect. Our findings demonstrate that the synergistic electronic coupling between multiple components can enhance the peroxidase activity, which can facilitate the development of an effective, facile, and reliable method to perform colorimetric immunoassays of H₂O₂ and cancer cells.

Structural insight into the biological functions of Arabidopsis thaliana ACHT1

The Arabidopsis thaliana atypical Cys His-rich thioredoxins (ACHTs) are a small class of atypical thioredoxins (TRXs) located in chloroplasts thylakoids and are characterized by a noncanonical motif at their redox active site, C (G/S)(S/G)C. Previous studies have reported that ACHT1 can interact with A. thaliana 2-Cys peroxiredoxins (2-Cys Prxs, including PrxA and PrxB) to transmit oxidation signals in response to illumination with normal light intensity. In this study, we reported the crystal structure of ACHT1 and show that ACHT1 adopts a canonical TRX fold. Comparison of the structures of ACHT1 in both reducing and oxidizing environments revealed that while the redox environment did not influence the overall structure of ACHT1, it did change the conformation of its catalytic residues. We found that the catalytic C125 of ACHT1 is the target residue for PrxA in vitro. In addition, we found that ACHT1 can reduce the peroxidase activity of PrxA, and further confirmed that the ability of ACHT1 to restore the peroxidase function of PrxA was due to the interaction between the two. Our results provide a structural basis for studying the function of atypical TRXs and the oxidative regulation mechanism of ACHT1 and 2-Cys Prxs in chloroplasts.

Heme•G-Quadruplex DNAzymes: Conditions for Maximizing Their Peroxidase Activity

Catalytic DNAs (DNAzymes) with peroxidase-like activity have great potential in bioanalytical chemistry [1], owing to numerous advantages that DNA enzymes offer over conventional protein enzymes, including structural simplicity, low cost, thermal stability, and straightforward handling and preparation. Maximizing the efficiency of the peroxidase activity of such DNAzymes is a subject in need of review. In this chapter, we discuss the optimal experimental conditions for the peroxidase activity of these DNAzymes and describe general procedures for their utilization.

High-affinity binding and catalytic activity of His/Tyr-based sequences: Extending heme-regulatory motifs beyond CP

BACKGROUND & MOTIVATION

Peptides and proteins can interact with heme through His, Tyr, or Cys in heme-regulatory motifs (HRMs). The Cys-Pro dipeptide is a well investigated HRM, but for His and Tyr such a distinct motif is currently unknown. In addition, many heme-peptide complexes, such as heme-amyloid β, can display a peroxidase-like activity, albeit there is little understanding of how the local primary and secondary coordination environment influences catalytic activity. We thus systematically evaluated a series of His- and Tyr-based peptides to identify sequence features for high-affinity heme binding and their impact on the catalytic activity of heme.

METHODS

We employed solid-phase peptide synthesis to produce 58 nonapeptides, which were investigated by UV/vis, resonance Raman, and 2D NMR spectroscopy. A chromogenic assay was used to determine the catalytic activity of the heme-peptide complexes.

RESULTS

Heme-binding affinity and binding mode were found to be dependent on the coordinating amino acid and spacer length between multiple potential coordination sites in a motif. In particular, HXH and HXXXH motifs showed strong heme binding. Analysis of the peroxidase-like activity revealed that some of these peptides and also HXXXY motifs enhance the catalytic activity of heme significantly.

CONCLUSIONS

We identify HXH, HXXXH, and HXXXY as potential new HRMs with functional properties. Several peptides displayed a strikingly high peroxidase-like activity.

GENERAL SIGNIFICANCE

The identification of HRMs allows to discover yet unknown heme-regulated proteins, and consequently, enhances our current understanding of pathologies involving labile heme.

Improved spectrophotometric assay for lytic polysaccharide monooxygenase

BACKGROUND

The availability of a sensitive and robust activity assay is a prerequisite for efficient enzyme production, purification, and characterization. Here we report on a spectrophotometric assay for lytic polysaccharide monooxygenase (LPMO), which is an advancement of the previously published 2,6-dimethoxyphenol (2,6-DMP)-based LPMO assay. The new assay is based on hydrocoerulignone as substrate and hydrogen peroxide as cosubstrate and aims toward a higher sensitivity at acidic pH and a more reliable detection of LPMO in complex matrices like culture media.

RESULTS

An LPMO activity assay following the colorimetric oxidation of hydrocoerulignone to coerulignone was developed. This peroxidase activity of LPMO in the presence of hydrogen peroxide can be detected in various buffers between pH 4-8. By reducing the substrate and cosubstrate concentration, the assay has been optimized for minimal autoxidation and enzyme deactivation while maintaining sensitivity. Finally, the optimized and validated LPMO assay was used to follow the recombinant expression of an LPMO in Pichia pastoris and to screen for interfering substances in fermentation media suppressing the assayed reaction.

CONCLUSIONS

The biphenol hydrocoerulignone is a better substrate for LPMO than the monophenol 2,6-DMP, because of a ~ 30 times lower apparent K _M value and a 160 mV lower oxidation potential. This greatly increases the measured LPMO activity when using hydrocoerulignone instead of 2,6-DMP under otherwise similar assay conditions. The improved activity allows the adaptation of the LPMO assay toward a higher sensitivity, different buffers and pH values, more stable assay conditions or to overcome low concentrations of inhibiting substances. The developed assay protocol and optimization guidelines increase the adaptability and applicability of the hydrocoerulignone assay for the production, purification, and characterization of LPMOs.

Improved performances of catalytic G-quadruplexes (G4-DNAzymes) via the chemical modifications of the DNA backbone to provide G-quadruplexes with double 3'-external G-quartets

Here we report on the design of a new catalytic G-quadruplex-DNA system (G4-DNAzyme) based on the modification of the DNA scaffold to provide the DNA pre-catalyst with two identical 3'-ends, known to be more catalytically proficient than the 5'-ends. To this end, we introduced a 5'-5' inversion of polarity site in the middle of the G4-forming sequences AG₄A and AG₆A to obtain d(^3'AGG^5'-^5'GGA^3') (or AG₂-G₂A) and d(^3'AGGG^5'-^5'GGGA^3') (or AG₃-G₃A) that fold into stable G4 whose tetramolecular nature was confirmed via nuclear magnetic resonance (NMR) and circular dichroism (CD) investigations. Both AG₂-G₂A and AG₃-G₃A display two identical external G-quartets (3'-ends) known to interact with the cofactor hemin with a high efficiency, making the resulting complex competent to perform hemoprotein-like catalysis (G4-DNAzyme). A systematic comparison of the performances of modified and unmodified G4s lends credence to the relevance of the modification exploited here (5'-5' inversion of polarity site), which represents a new chemical opportunity to improve the overall activity of catalytic G4s.

In Vitro Selection of DNA Aptamers for a Small-Molecule Porphyrin by Gold Nanoparticle-Based SELEX

In this study, a new strategy for the selection of aptamers against small-molecule target was established using gold nanoparticles (AuNPs) as the separation matrix and Zinc(II)-Protoporphyrin IX (ZnPPIX) as the target molecule without the immobilization step due to the absorption of ssDNA on AuNPs. The progress of the selection process was monitored by the recovery rate and the fluorescence enhancement of N-methyl mesoporphyrin IX (NMM) after reacting with each selected pool. After 11 rounds of selection, a truncated aptamer ZnP1.2 with a low-micromolar dissociation constant was obtained, and it also showed good fluorescence enhancement for NMM and the enhanced peroxidase activity after binding with hemin, indicating this functional aptamer has potential to be a light-up fluorescent probe and a DNAzyme which could be used as an alternative to peroxidases for many colorimetric or chemiluminescent detections in biosensing events. The experimental results show that the simple and convenient AuNP-based SELEX is very conducive to the selection of aptamers for small-molecule targets.

The Role of Peroxiredoxin Family in Cancer Signaling

Peroxiredoxins (Prxs) are antioxidant enzymes that protect cells from oxidative stress by reducing intracellular accumulation of reactive oxygen species (ROS). In mammalian cells, the six Prx isoforms are ubiquitously expressed in diverse intracellular locations. They are involved in the regulation of various physiological processes including cell growth, differentiation, apoptosis, immune response and metabolism as well as intracellular ROS homeostasis. Although there are increasing evidences that Prxs are involved in carcinogenesis of many cancers, their role in cancer is controversial. The ROS levels in cancer cells are increased compared to normal cells, thus promoting cancer development. Nevertheless, for various cancer types, an overexpression of Prxs has been found to be associated with poor patient prognosis, and an increasing number of studies have reported that tumorigenesis is either facilitated or inhibited by regulation of cancer-associated signaling pathways. This review summarizes Prx isoforms and their basic functions, the relationship between the expression level and the physiological role of Prxs in cancer cells, and their roles in regulating cancer-associated signaling pathways.

Tandem catalysis driven by enzymes directed hybrid nanoflowers for on-site ultrasensitive detection of organophosphorus pesticide

Accurate analysis of organophosphate pesticides (OPs) with portable devices remain an elusive goal that have received widespread investigative attention in the areas of environmental contamination and disease prevention. Herein, using all-in-one enzyme-inorganic hybrid nanoflowers (ACC-HNFs) to fabricate high-performance artificial enzyme cascade system, we established a sensitive and affordable lab-on-paper biosensor. This biosensor incorporated disposable screen-printed carbon electrode (SPCE) and colorimetric test strips, which enabled the dual-modal readout (electrochemical and colorimetric signal) for on-site monitoring of OPs, achieving an "on-demand" tuning of the detection performance. Using paraoxon as a model analyte, the ACC-HNFs-based lab-on-paper platform could reach a limit of detection down to the femtogram/mL level (6 fg mL^-1). Meticulous design of ACC-HNFs provided a versatile approach for constructing artificial enzyme as a recognizer and amplifier to fill the gap in constructing robust artificial enzyme systems which can be used for on-site contamination monitoring and biological diagnosis.

Quantification of carbonate radical formation by the bicarbonate-dependent peroxidase activity of superoxide dismutase 1 using pyrogallol red bleaching

Carbonate radicals (CO₃•^-) are generated by the bicarbonate-dependent peroxidase activity of cytosolic superoxide dismutase (Cu,Zn-SOD, SOD-1). The present work explored the use of bleaching of pyrogallol red (PGR) dye to quantify the rate of CO₃•^- formation from bovine and human SOD-1 (bSOD-1 and hSOD-1, respectively). This approach was compared to previously reported methods using electron paramagnetic resonance spin trapping with DMPO, and the oxidation of ABTS (2,2-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid). The kinetics of PGR consumption elicited by CO₃•^- was followed by visible spectrophotometry. Solutions containing PGR (5–200 μM), SOD-1 (0.3–3 μM), H₂O₂ (2 mM) in bicarbonate buffer (200 mM, pH 7.4) showed a rapid loss of the PGR absorption band centered at 540 nm. The initial consumption rate (R_i) gave values independent of the initial PGR concentration allowing an estimate to be made of the rate of CO₃•^- release of 24.6 ± 4.3 μM min⁻¹ for 3 μM bSOD-1. Both bSOD-1 and hSOD-1 showed a similar peroxidase activity, with enzymatic inactivation occurring over a period of 20 min. The single Trp residue (Trp³²) present in hSOD-1 was rapidly consumed (initial consumption rate 1.2 ± 0.1 μM min⁻¹) with this occurring more rapidly than hSOD-1 inactivation, suggesting that these processes are not directly related. Added free Trp was rapidly oxidized in competition with PGR. These data indicate that PGR reacts rapidly and efficiently with CO₃•^- resulting from the peroxidase activity of SOD-1, and that PGR-bleaching is a simple, fast and cheap method to quantify CO₃•^- release from bSOD-1 and hSOD-1 peroxidase activity.

•

CO₃•^- are released during the bicarbonate-dependent peroxidase activity of SOD-1.

•

The rate and extent of CO₃•^- release can be determined by pyrogallol red bleaching.

•

Inactivation of bSOD-1 and hSOD-1 occurs rapidly during the reaction.

•

SOD-1 inactivation is independent of the presence of pyrogallol red.

•

This assay should help elucidate protein oxidation/crosslinking mediated by SOD-1.

Prx2 links ROS homeostasis to stemness of cancer stem cells

Cancer stem cells (CSC) with low levels of reactive oxygen species (ROS) are resistant to conventional chemotherapy or radiation therapy. Peroxiredoxin 2 (Prx2) is a redox regulatory protein that plays a key role in maintaining ROS homeostasis in the tumor microenvironment. However, despite the role of Prx2 in ROS-mediated signal transduction, the association of Prx2 with stemness via ROS in CSC has not been thoroughly investigated. In this study, we investigated the link between Prx2 and CSC stemness through regulation of ROS levels in hepatocellular carcinoma (HCC) cells. ROS induced CSC stemness reduction and downregulated stem cell markers in Huh7 and SK-HEP1 cells. Prx2 knockdown decreased CSC sphere formation and expression of stem cell makers with increasing intracellular ROS levels. This effect was reversed by the ROS scavengers NAC and GSH in Prx2 knockdown cells. Conversely, we found that Prx2 overexpression promotes CSC stemness and the peroxidase activity of Prx2 is essential for CSC stemness using peroxidase inactive mutant, Prx2^C51/172S. More importantly, the hyperoxidation-resistant mutant (Prx2^ΔYF), which has a constant ROS scavenging activity even at high concentrations of ROS, increased the CSC stemness and expression of stem cell markers more than Prx2^WT under oxidative stress. Taken together, our findings demonstrate that Prx2 links ROS homeostasis to CSC stemness; Prx2 is a mediator between ROS homeostasis and CSC stemness.

Measurements for Sulfide-Mediated Inhibition of Myeloperoxidase Activity

Oxidative stress-alleviating and inflammation-mediatory functions of hydrogen sulfide were reported to be key features of its biological actions. However, the underlying molecular mechanisms of these biological observations are not fully understood. In conditions where sulfide was proposed to be protective against oxidative stress- or inflammation-induced tissue damage (e.g., reperfusion injury, atherosclerosis, vascular inflammation), the reactive oxidant-producing function of a key neutrophil enzyme, myeloperoxidase, was reported to be a protagonist on the detrimental side. We recently described favorable interactions between sulfide and myeloperoxidase and proposed that the potent inhibition of myeloperoxidase activities could contribute to sulfide's beneficial functions in a number of cardiovascular pathologies. Our chapter is dedicated to aid future studies and drug development endeavors in this area by providing methodological guidance on how to assess the inhibitory potential of sulfide on myeloperoxidase enzymatic activities in isolated protein systems, in neutrophil homogenates, and in live neutrophil preparations.

Process kinetics on physico-chemical and peroxidase activity for different blanching methods of sweet corn

Blanching was performed to inactivate the enzyme using microwave, steam and hot water blanching methods and effect on the enzymatic activity, chemical properties and physical properties of the sweet corn were studied. The effectiveness of each blanching process was evaluated by measuring the loss of peroxidase activity, which was lost after 60, 90 and 120 s with k-values 0.016, 0.024 and 0.028 s^-1 following first order kinetics for microwave, steam and hot water blanching respectively. The total sugar, ascorbic acid, moisture content, kernel mass and geometric diameter changed from 8.40 to 6.30, 7.20 and 7.50 g/100 g; 7.15 to 5.70, 6.10 and 6.60 mg/100 g; 76 to 79.20, 78.20 and 75.30%; 0.47 to 0.53, 0.50 and 0.42 g; 8.00 to 8.50, 8.30 and 7.20 mm at optimum level of blanching during microwave, steam and hot water blanching respectively, indicating higher retention of total sugar and ascorbic acid in microwave blanching. The change in colour, especially increase in brownness was observed during blanching processes. The average R² for zero-order model was 0.945, suggesting use of model for prediction of physico-chemical parameters during blanching process of sweet corn.

Ni-hemin metal-organic framework with highly efficient peroxidase catalytic activity: toward colorimetric cancer cell detection and targeted therapeutics

Background

Given the great benefits of artificial enzymes, a simple approach is proposed via assembling of Ni²⁺ with hemin for synthesis of Ni-hemin metal–organic-frameworks (Ni-hemin MOFs) mimic enzyme. The formation of the Ni-hemin MOFs was verified by scanning electron microscopy, Transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Energy-dispersive X-ray spectroscopy and UV–vis absorption spectroscopy. This novel nanocomposite exhibited surprising peroxidase like activity monitored by catalytic oxidation of a typical peroxidase substrate, 3,3,5,5′-tetramethylbenzidine, in the presence of H₂O₂. By using folic acid conjugated MOF nanocomposite as a recognition element, we develop a colorimetric assay for the direct detection of cancer cells.

Results

The proposed sensor presented high sensitivity and selectivity for the detection of human breast cancer cells (MCF-7) and Human Caucasian gastric adenocarcinoma. By measuring UV–vis absorbance response, a wide detection range from 50 to 10⁵ cells/mL with a detection limit as low as 10 cells/mLwas reached for MCF-7 cells. We further discuss therapeutics efficiency of Ni-hemin MOFs in the presence of H₂O₂ and ascorbic acid. Peroxidase-mimic Ni-hemin MOFs as reactive oxygen species which could damage MCF-7 cancer cells, however for normal cells (human embryonic kidney HEK 293 cells) killing effect was negligible.

Conclusions

Based on these behaviors, the developed method offers a fast, easy and cheap assay for the interest in future diagnostic and treatment application.

Relating the multi-functionality of cytochrome c to membrane binding and structural conversion

Cytochrome c is known as an electron-carrying protein in the respiratory chain of mitochondria. Over the last 20 years, however, alternative functions of this very versatile protein have become the focus of research interests. Upon binding to anionic lipids such as cardiolipin, the protein acquires peroxidase activity. Multiple lines of evidence suggest that this requires a conformational change of the protein which involves partial unfolding of its tertiary structure. This review summarizes the current state of knowledge of how cytochrome c interacts with cardiolipin-containing surfaces and how this affects its structure and function. In this context, we delineate partially conflicting results regarding the affinity of cytochrome c binding to cardiolipin-containing liposomes of different size and its influence on the structure of the protein and the morphology of the membrane.

Functionalized Nano-adsorbent for Affinity Separation of Proteins

Thiol-functionalized silica nanospheres (SiO₂-SH NSs) with an average diameter of 460 nm were synthesized through a hydrothermal route. Subsequently, the prepared SiO₂-SH NSs were modified by SnO₂ quantum dots to afford SnO₂/SiO₂ composite NSs possessing obvious fluorescence, which could be used to trace the target protein. The SnO₂/SiO₂ NSs were further modified by reduced glutathione (GSH) to obtain SnO₂/SiO₂-GSH NSs, which can specifically separate glutathione S-transferase-tagged (GST-tagged) protein. Moreover, the peroxidase activity of glutathione peroxidase 3 (GPX3) separated from SnO₂/SiO₂-GSH NSs in vitro was evaluated. Results show that the prepared SnO₂/SiO₂-GSH NSs exhibit negligible nonspecific adsorption, high concentration of protein binding (7.4 mg/g), and good reused properties. In the meantime, the GST-tagged GPX3 separated by these NSs can retain its redox state and peroxidase activity. Therefore, the prepared SnO₂/SiO₂-GSH NSs might find promising application in the rapid separation and purification of GST-tagged proteins.

A fast and sensitive activity assay for lytic polysaccharide monooxygenase

BACKGROUND

Lytic polysaccharide monooxygenases (LPMO) release a spectrum of cleavage products from their polymeric substrates cellulose, hemicellulose, or chitin. The correct identification and quantitation of these released products is the basis of MS/HPLC-based detection methods for LPMO activity. The duration, effort, and intricate analysis allow only specialized laboratories to measure LPMO activity in day-to-day work. A spectrophotometric assay will simplify the screening for LPMO in culture supernatants, help monitor recombinant LPMO expression and purification, and support enzyme characterization.

RESULTS

Based on a newly discovered peroxidase activity of LPMO, we propose a fast, robust, and sensitive spectrophotometric activity assay using 2,6-dimethoxyphenol (2,6-DMP) and H2O2. The fast enzymatic assay (300 s) consists of 1 mM 2,6-DMP as chromogenic substrate, 100 µM H2O2 as cosubstrate, and an adequate activity of LPMO in a suitable buffer. The high molar absorption coefficient of the formed product coerulignone (ε469 = 53,200 M-1 cm-1) makes the assay sensitive and allows reliable activity measurements of LPMO in concentrations of approx. 0.5-50 mg L-1.

CONCLUSIONS

The activity assay based on 2,6-DMP detects a novel peroxidase activity of LPMO. This activity can be accurately measured and used for enzyme screening, production, and purification, and can also be applied to study binding constants or thermal stability. However, the assay has to be used with care in crude extracts, because other enzymes such as laccase or peroxidase will interfere with the assay. We also want to stress that the peroxidase activity is a homogeneous reaction with soluble substrates and should not be correlated to heterogeneous LPMO activity on polymeric substrates.

Humanlike substitutions to Ω-loop D of yeast iso-1-cytochrome c only modestly affect dynamics and peroxidase activity

Structural studies of yeast iso-1-cytochrome c (L.J. McClelland, T.-C. Mou, M.E. Jeakins-Cooley, S.R. Sprang, B.E. Bowler, Proc. Natl. Acad. Sci. U.S.A. 111 (2014) 6648-6653) show that modest movement of Ω-loop D (residues 70-85, average RMSD versus the native structure: 0.81 Å) permits loss of Met80-heme ligation creating an available coordination site to catalyze the peroxidase activity mediated by cytochrome c early in apoptosis. However, Ala81 and Gly83 move significantly (RMSDs of 2.18 and 1.26 Å, respectively). Ala81 and Gly83 evolve to Ile and Val, respectively, in human cytochrome c and peroxidase activity decreases 25-fold relative to the yeast protein at pH 7. To test the hypothesis that these residues evolved to restrict the peroxidase activity of cytochrome c, A81I and G83V variants of yeast iso-1-cytochrome c were prepared. For both variants, the apparent pK_a of the alkaline transition increases by 0.2 to 0.3 relative to the wild type (WT) protein and the rate of opening the heme crevice is slowed. The cooperativity of acid unfolding is decreased for the G83V variant. At pH 7 and 8, the catalytic rate constant, k_cat, for the peroxidase activity of both variants decreases relative to WT, consistent with the effects on alkaline isomerization. Below pH 7, the loss in the cooperativity of acid unfolding causes k_cat for peroxidase activity to increase for the G83V variant relative to WT. Neither variant decreases k_cat to the level of the human protein, indicating that other residues also contribute to the low peroxidase activity of human cytochrome c.