Systematic engineering of Saccharomyces cerevisiae for efficient synthesis of hemoglobins and myoglobins

Hemoglobin (Hb) and myoglobin (Mb) are kinds of heme-binding proteins that play crucial physiological roles in different organisms. With rapid application development in food processing and biocatalysis, the requirement of biosynthetic Hb and Mb is increasing. However, the production of Hb and Mb is limited by the lower expressional level of globins and insufficient or improper heme supply. After selecting an inducible strategy for the expression of globins, removing the spatial barrier during heme synthesis, increasing the synthesis of 5-aminolevulinate and moderately enhancing heme synthetic rate-limiting steps, the microbial synthesis of bovine and porcine Hb was firstly achieved. Furthermore, an engineered Saccharomyces cerevisiae obtained a higher titer of soybean (108.2 ± 3.5 mg/L) and clover (13.7 ± 0.5 mg/L) Hb and bovine (68.9 ± 1.6 mg/L) and porcine (85.9 ± 5.0 mg/L) Mb. Therefore, this systematic engineering strategy will be useful to produce other hemoproteins or hemoenzymes with high activities.

The effect of acute acid exposure on immunomodulatory protein secretion, cell survival, and cell cycle progression in tumour cell lines

Cancer develops when multiple systems fail to suppress uncontrolled cell proliferation. Breast cancers and oesophageal squamous cell carcinoma (OSCC) are common cancers prone to genetic instability. They typically occur in acidic microenvironments which impacts on cell proliferation, apoptosis, and their influence on surrounding cells to support tumour growth and immune evasion. This study aimed to evaluate the impact of the acidic tumour microenvironment on the production of pro-tumorigenic and immunomodulatory factors in cancer cell lines. Multiple factors that may mediate immune evasion were secreted including IL-6, IL-8, G-CSF, IP-10, GDF-15, Lipocalin-2, sICAM-1, and myoglobin. Others, such as VEGF, FGF, and EGF that are essential for tumour cell survival were also detected. Treatment with moderate acidity did not significantly affect secretion of most proteins, whereas very low pH did. Distinct differences in apoptosis were noted between the cell lines, with WHCO6 being better adapted to survive at moderate acid levels. Conditioned medium from acid-treated cells stimulated increased cell viability and proliferation in WHCO6, but increased cell death in MCF-7. This study highlights the importance of acidic tumour microenvironment in controlling apoptosis, cell proliferation, and immune evasion which may be different at different anatomical sites. Immunomodulatory molecules and growth factors provide therapeutic targets to improve the prognosis of individuals with cancer.

Studies on the binding of CO to low-spin [Fe(II)(Por)L2] complexes: an aid to understanding the binding of CO to haemoglobin and myoglobin

The visible and Mössbauer spectra of [Fe(II)(Por)L₂] and [Fe(II)(Por)L(CO)] complexes (where Por = protoporphyrin IX (PPIX) or tetra(p-sulfophenyl)porphyrin (TPPS) and L = an aliphatic or aromatic nitrogenous base) are reported and discussed. The results are compared to those of previously reported [Fe(II)(Por)L(CO)] complexes (where Por = PPIX, TPPS, PMXPP, TPP, OMTBP and OEP; L = a nitrogenous aromatic ligand) and HbCO (where Hb = haemoglobin) and MyCO (where My = myoglobin). A new approach, to extracting information from the Mössbauer parameters has been developed by plotting those of the [Fe(II)(Por)L₂] complexes against those of [Fe(II)(Por)L(CO)] complexes for the same ligands, has yielded a series of trend lines that show a significant dependence on both the nature of the porphyrin and also of the nitrogenous ligand. Different trend lines were found for aromatic nitrogenous ligands to aliphatic nitrogenous ligands showing that the porphyrins could donate different amounts of charge to the Fe(II) cations as the L ligand changed, and hence, they display electron sink properties. From the plots, it was shown that haemoglobin and myoglobin both bind CO very strongly compared to the model complexes studied herein. Using the reported structural and Mössbauer data for the [Fe(II)(Por)L₂] and [Fe(II)(Por)L(CO)] complexes, it proved possible and instructive to plot the Mössbauer parameters against a number of the bond lengths around the Fe(II) cations. The interpretation of the resulting trend lines both supported and facilitated the extension of our findings enabling further understanding of the geometry of the bonding in CO haemoglobin and CO myoglobin.

Application of simultaneous ultrasonic curing on pork (Longissimus dorsi): Mass transport of NaCl, physical characteristics, and microstructure

This study aimed to investigate the effect of ultrasound curing with various working modes and frequency combinations, including mono-, dual- and tri-frequency, on the content of NaCl and tenderness of pork loins (Longissimus dorsi). The physical qualities, myoglobin, moisture migration, distribution, and microstructure of pork were also evaluated. The results displayed that the NaCl content of samples cured by simultaneous ultrasound (100 W/L) working mode with a frequency combination of 20, 40, and 60 kHz was higher than that of other ultrasound working modes. The effect of ultrasonic brining was significantly better than the static curing when the saline solution was >35 mL. In addition, the samples cured by simultaneous ultrasound had better physical qualities, including more pickling absorptivity, less cooking loss, and lower hardness, tenderness, and chewiness value. The intensity of lightness was reduced, although redness and yellowness remained unaltered compared to static curing. The myoglobin content decreased drastically without changing the oxygenation level, and the relaxation time of T_2b and T₂₁ was delayed. The microstructure indicated that the ultrasonic treatment could promote changes in meat texture. Overall, the simultaneous ultrasound at various frequencies could efficiently accelerate NaCl penetration and improve pork quality.

Resonance Raman Characterization of O2-Binding Heme Proteins

A vast array of critical in vivo processes and pathways are dependent on a multitude of O₂-binding heme proteins which contain a diverse range of functions. Resonance Raman (rR) spectroscopy is an ideal technique for structural investigation of these proteins, providing information about the geometry of the Fe-O-O fragment and its electrostatic interactions with the distal active site. Characterization of these oxy adducts is an endeavor that is complicated by their instability for many heme proteins in solution, an obstacle which can be overcome by applying the rR technique to cryogenically frozen samples. We describe here how to measure rR spectra of heme proteins with stable oxy forms, as well as the technical adaptations required to measure unstable samples at 77 K.

Extracorporeal Removal of Myoglobin in Patients with Rhabdomyolysis and Acute Kidney Injury: Comparison of High and Medium Cut-Off Membrane and an Adsorber Cartridge

INTRODUCTION

The role of extracorporeal myoglobin removal in the treatment of rhabdomyolysis-associated severe acute kidney injury (AKI) is not yet fully established. High cut-off (HCO) and medium cut-off (MCO) dialysis membrane and cytokine adsorber (CytoSorb®) have been used to this purpose in clinical practice. The data on comparative effectiveness of those methods are scarce.

METHODS

In this single-center retrospective study, we included patients with AKI and concomitant rhabdomyolysis (myoglobin >20,000 μg/L), who underwent at least one extracorporeal myoglobin removal procedure. The main outcome parameter was myoglobin reduction ratio, whereas albumin was assessed as a safety parameter.

RESULTS

We analyzed data for 15 patients, who underwent 28 procedures (13 HCO, 9 MCO, and 6 adsorber). Pre-treatment serum myoglobin levels were similar between the groups and myoglobin reduction was significant in HCO (p = 0.03) and MCO groups (p < 0.01) and borderline significant in adsorber group (p = 0.06). Reduction ratios were comparable between the groups (median 0.64 (inter-quartile range IQR 0.13-0.72), 0.54 (IQR 0.51-0.61) and 0.50 (IQR 0.37-0.62), respectively, p = 0.83). Both pre- and post-procedure serum albumin levels were significantly lower in the MCO group. However, with routine albumin substitution in the HCO group only, serum albumin remained stable during the procedures in all subgroups.

CONCLUSIONS

Novel MCO membrane might represent the optimal mode of treatment of severe rhabdomyolysis-associated AKI, as it allows for efficient removal of myoglobin, avoids albumin supplementation and is associated with lower costs. For patients requiring cytokine removal, the adsorption capsule can simultaneously reduce cytokine and myoglobin levels.

Acute diquat poisoning causes rhabdomyolysis

We studied the case of a 36-year-old female patient who self-administered about 30 ml of diquat solution (200 g/L) during a suicide attempt. She developed nausea, vomiting, dizziness, and weakness in her limbs and was admitted to the emergency department of our hospital 4 h later. The patient developed progressive swelling and pain in both calves 12 h after admission. Based on symptoms, lower limb color Doppler ultrasound, and elevated levels of myoglobin and creatine kinase, the patient was diagnosed with rhabdomyolysis caused by diquat poisoning. The patient recovered and was discharged after treatment with hemoperfusion, continuous venovenous hemodialysis, acid suppression, liver protection, low-dose glucocorticoids, etc. Rhabdomyolysis caused by diquat poisoning has not been previously reported. We attempted to analyze the mechanism of this symptom through a literature review. We recommend the routine monitoring of creatine phosphokinase (CK) and myoglobin (MYO) in patients with diquat poisoning to avoid missed diagnosis. Further, the mechanism of this poisoning symptom was discussed through the literature review.

Myoglobin mutant with enhanced nitrite reductase activity regulates intracellular oxidative stress in human breast cancer cells

Heme proteins play vital roles in regulating the reactive oxygen/nitrogen species (ROS/RNS) levels in cells. In this study, we overexpressed human wild-type (WT) myoglobin (Mb) and its double mutant, F43H/H64A Mb with enhanced nitrite reductase (NIR) activity, in the typical representative triple-negative breast cancer cell, MDA-MB-231 cells. The results showed that the overexpression of F43H/H64A Mb increased the level of nitric oxide (NO) and the degree of oxidative stress, and then activated Akt/MAPK mediated apoptotic cascade, whereas WT Mb showed the opposite effect. This study indicates that Mb plays an important role in maintaining the balance of the cellular redox system and could thus be a valuable target for cancer therapy.

Low-frequency EPR of ferrimyoglobin fluoride and ferrimyoglobin cyanide: a case study on the applicability of broadband analysis to high-spin hemoproteins and to HALS hemoproteins

An EPR spectrometer has been developed that can be tuned to many frequencies in the range of ca 0.1–15 GHz. Applicability has been tested on ferrimyoglobin fluoride (MbF) and ferrimyoglobin cyanide (MbCN). MbF has a high-spin (S = 5/2) spectrum with ¹⁹F superhyperfine splitting that is only resolved in X-band along the heme normal. Low-frequency EPR also resolves the splitting in the heme plane. Measurement of linewidth as a function of frequency provides the basis for an analysis of inhomogeneous broadening in terms of g-strain, zero-field distribution, unresolved superhyperfine splittings and dipolar interaction. Rhombicity in the g tensor is found to be absent. MbCN (S = 1/2) has a highly anisotropic low spin (HALS) spectrum for which g_x cannot be determined unequivocally in X-band. Low-frequency EPR allows for measurement of the complete spectrum and determination of the g-tensor.

Color attributes and myoglobin chemistry exhibit relationships with tenderness and calpain-1 abundance in postmortem Longissimus lumborum muscles from Holstein heifers

The objective of this study was to determine the extent that myoglobin and beef color are associated with calpain-1 relative abundance relative and tenderness. Longissimus lumborum (LL) samples from the left side of Holstein beef carcasses (n = 31) were collected immediately post-evisceration for 0 h analyses. At 48 h postmortem six steaks were removed from the right side of each carcass for analyses at 48 and 336 h postmortem. Myoglobin concentrations resulted in negative correlations (P < 0.05) to Warner-Bratzler shear force (WBSF) values at 336 h postmortem. L*, a*, and b* values at 48 h resulted in positive correlations (P < 0.05) with WBSF values at 48 and 336 h. Values for b* at 336 h had positive correlations with calpain-1 concentration at 0 and 336 h. Data from this study indicate a potential relationship between myoglobin concentration and meat color with tenderness aspects and calpain-1 relative abundance.

Paradoxical effects of lipolysis on the lipid oxidation in meat and meat products

Lipolysis in meat and meat products is a phenomenon involving hydrolysis of lipids, notably via enzymatic catalysis that takes place even postmortem. During refrigerated and frozen storage of meat, in particular fish, endogenous lipolytic enzymes actively degrade triacylglycerols and phospholipids resulting in accumulation of free fatty acids and other hydrolytic products. A classical conjecture suggests that lipolysis enhances lipid oxidation which is involved in quality deterioration of fresh meat and, to some degrees, flavor development of certain meat products. Recent studies (<5 years) have shown that under some circumstances, lipolysis of certain lipolytic enzymes can inhibit lipid oxidation in muscle models, which provides more insight in lipid oxidation mechanisms in muscle matrices as well as implies potential strategies for improving meat quality. This review will discuss such paradoxical effects and potential mechanisms of lipolysis on lipid oxidation in meat and meat products.

Myoglobin from Atlantic and Tinker mackerels: Purification, characterization and its possible use as a molecular marker

Here, we report the characterization (purification, autoxidation rate, pseudoperoxidase activity) and amino acid sequence determination of S. scombrus (Atlantic mackerel) and S. colias (Tinker mackerel) mioglobins (Mbs), considering the increasing consumption of fresh and canned mackerel meat and Mb implication in meat storage (e.g.: browning and lipid oxidation). We found that Atlantic mackerel Mb has major autoxidation rate (0.204 ± 0.013 h^-1) compared to Tinker mackerel Mb (0.140 ± 0.009 h^-1), while the pseudoperoxidase activity is major for Tinker mackerel (K_m: 87.71 ± 7.19 μM; k_cat: 0.32 s^-1) Mb with respect to Atlantic mackerel (K_m: 96.08 ± 6.91 μM; k_cat: 0.50 s^-1). These functional differences are confirmed by primary structure determination, in which six amino acid substitutions are found, with the first N-terminal amino acid residue acetylated. Furthermore, we predicted by AphaFold 3D model both fish Mbs and used them to investigate the possible structural differences. In addition, phylogenetic analysis using Mb sequences from Scombridae family confirms that Atlantic and Tinker mackerels are two distinct species. Finally, an analytic qualitative RP-HPLC method to distinguish S. scombrus and S. colias specimens was developed considering the different retention times of the two mackerel apoMbs.

Myoglobin expression by alternative transcript in different mesenchymal stem cells compartments

BACKGROUND

The metabolic phenotype of stem cells is increasingly recognized as a hallmark of their pluripotency with mitochondrial and oxygen-related metabolism playing a not completely defined role in this context. In a previous study, we reported the ectopic expression of myoglobin (MB) in bone marrow-derived hematopoietic stem/progenitor cells. Here, we have extended the analysis to mesenchymal stem cells (MSCs) isolated from different tissues.

METHODS

MSCs were isolated from human placental membrane, mammary adipose tissue and dental pulp and subjected to RT-PCR, Western blotting and mass spectrometry to investigate the expression of MB. A combination of metabolic flux analysis and cyto-imaging was used to profile the metabolic phenotype and the mitochondria dynamics in the different MSCs.

RESULTS

As for the hematopoietic stem/progenitor cells, the expression of Mb was largely driven by an alternative transcript with the protein occurring both in the monomer and in the dimer forms as confirmed by mass spectrometry analysis. Comparing the metabolic fluxes between neonatal placental membrane-derived and adult mammary adipose tissue-derived MSCs, we showed a significantly more active bioenergetics profile in the former that correlated with a larger co-localization of myoglobin with the mitochondrial compartment. Differences in the structure of the mitochondrial network as well as in the expression of factors controlling the organelle dynamics were also observed between neonatal and adult mesenchymal stem cells. Finally, the expression of myoglobin was found to be strongly reduced following osteogenic differentiation of dental pulp-derived MSCs, while it was upregulated following reprogramming of human fibroblasts to induce pluripotent stem cells.

CONCLUSIONS

Ectopic expression of myoglobin in tissues other than muscle raises the question of understanding its function therein. Properties in addition to the canonical oxygen storage/delivery have been uncovered. Finding of Mb expressed via an alternative gene transcript in the context of different stem cells with metabolic phenotypes, its loss during differentiation and recovery in iPSCs suggest a hitherto unappreciated role of Mb in controlling the balance between aerobic metabolism and pluripotency. Understanding how Mb contributes through modulation of the mitochondrial physiology to the stem cell biology paves the way to novel perspectives in regenerative medicine as well as in cancer stem cell therapy.

Development of novel aptasensor for ultra-sensitive detection of myoglobin via electrochemical signal amplification of methylene blue using poly (styrene)-block-poly (acrylic acid) amphiphilic copolymer

Amplification of electrochemical signal in order to betterment of limit of detection in determination of biomarkers has an important role in early detection of some dangerous diseases such as cancers. For this purpose, in this research, two types of poly (styrene)-block-poly (acrylic acid) amphiphilic copolymer (PS₆₁-b-PAA₅₉₆ and PS₅₉₆-b-PAA₆₁) were synthesized by controlled radical polymerization method via reversible addition-fragmentation chain transfer polymerization (RAFT) technique. Chemical structure of block copolymers was confirmed by FT-IR spectroscopy and their surface morphology was assessed by scanning electron microscopy (SEM). Self-assembly of these block copolymers into polymeric vesicles (polymersomes), loading and release efficiency of methylene blue as an electroactive indicator were investigated in DMF and THF solvents. On the basis of our findings PS₆₁-b-PAA₅₉₆ has better capability for loading and release of MB than PS₅₉₆-b-PAA₆₁. Then the obtained methylene blue-loaded polymersome successfully used for development of an aptasensor toward determination of trace amounts of myoglobin. The proposed aptasensor showed a wide linear range from 1.0 aM to 1.0 μM with an ultra-low detection limit of 0.73 aM. Applying this amplification strategy, determination of myoglobin in real samples was successfully performed.

Oxygen flux from capillary to mitochondria: integration of contemporary discoveries

Resting humans transport ~ 100 quintillion (10¹⁸) oxygen (O₂) molecules every second to tissues for consumption. The final, short distance (< 50 µm) from capillary to the most distant mitochondria, in skeletal muscle where exercising O₂ demands may increase 100-fold, challenges our understanding of O₂ transport. To power cellular energetics O₂ reaches its muscle mitochondrial target by dissociating from hemoglobin, crossing the red cell membrane, plasma, endothelial surface layer, endothelial cell, interstitial space, myocyte sarcolemma and a variable expanse of cytoplasm before traversing the mitochondrial outer/inner membranes and reacting with reduced cytochrome c and protons. This past century our understanding of O₂'s passage across the body's final O₂ frontier has been completely revised. This review considers the latest structural and functional data, challenging the following entrenched notions: (1) That O₂ moves freely across blood cell membranes. (2) The Krogh-Erlang model whereby O₂ pressure decreases systematically from capillary to mitochondria. (3) Whether intramyocyte diffusion distances matter. (4) That mitochondria are separate organelles rather than coordinated and highly plastic syncytia. (5) The roles of free versus myoglobin-facilitated O₂ diffusion. (6) That myocytes develop anoxic loci. These questions, and the intriguing notions that (1) cellular membranes, including interconnected mitochondrial membranes, act as low resistance conduits for O₂, lipids and H⁺-electrochemical transport and (2) that myoglobin oxy/deoxygenation state controls mitochondrial oxidative function via nitric oxide, challenge established tenets of muscle metabolic control. These elements redefine muscle O₂ transport models essential for the development of effective therapeutic countermeasures to pathological decrements in O₂ supply and physical performance.

A membraneless self-powered photoelectrochemical biosensor based on Bi2S3/BiPO4 heterojunction photoanode coupling with redox cycling signal amplification strategy

The photoelectrochemical (PEC) self-powered system has attracted great attention in disease detection. The determination of a simple and efficient approach for disease-related biomarkers is highly interesting and appealing. Herein, an ingenious visible light-induced membraneless self-powered PEC biosensing platform was constructed, integrating a signal amplification strategy for ultrasensitive split-type PEC bioanalysis. The system was comprised of a Bi₂S₃/BiPO₄ heterojunction photoanode and a platinum (Pt) cathode in a one compartment chamber. An alkaline phosphatase (ALP)-loaded sandwich immunoassay was used to generate the signal reporter ascorbic acid (AA) in a 96-well plate, and myoglobin (Myo) was used as a model protein. In the presence of AA, ferrocene (Fc), and Tris (2-carboxyethyl) phosphine (TCEP), the chemical-chemical redox cycling scheme was operated upon the initial oxidation of Fc by the holes in the Bi₂S₃/BiPO₄ photoelectrode, and Fc was regenerated from Fc⁺ by AA. Subsequently, AA was regenerated by TCEP after its oxidation, and cycling was triggered. As a result, the proposed self-powered PEC sensing exhibited excellent performance with a wide linear range from 5.0 × 10^-13 to 1.0 × 10^-7 g/mL, and a low detection limit of 2.0 × 10^-13 g/mL for Myo. This work provided a new design of a redox cycling strategy in the self-powered PEC biosensor, and showed an effective approach for the clinical diagnosis.

Biophysical and mass spectrometry based characterization of methylglyoxal-modified myoglobin: Role of advanced glycation end products in inducing protein structural alterations

Methylglyoxal (MG) is a highly reactive α-dicarbonyl compound which reacts with proteins to form advanced glycation end products (AGEs). MG-induced AGE (MAGE) formation is particularly significant in diabetic condition. In the current study, we have undertaken a time-dependant characterization of MG-modified myoglobin following incubation of the heme protein with the α-dicarbonyl compound for different time periods. Interestingly, mass spectrometric studies indicated modifications at two specific lysine residues, Lys-87 and Lys-133. The AGE adducts identified at Lys-87 were carboxymethyllysine and carboxyethyllysine, while those detected at Lys-133 included pyrraline-carboxymethyllysine and carboxyethyllysine, respectively. Far-UV CD studies revealed a decrease in the native α-helical content of the heme protein gradually with increasing time of MG incubation. In addition, MG modification was found to induce changes in tertiary structure as well as surface hydrophobicity of the heme protein. MG-derived AGE adducts thus appear to alter the structure of Mb considerably. Considering the increased level of MG in diabetic condition, the current study appears physiologically relevant in terms of understanding AGE-mediated protein modification and subsequent structural changes.

Inherent factors influence color variations in semimembranosus muscle of pigs

Variations in color, though a quality frustration, are common across the face of fresh and processed hams. Herein, we measured objective color across the semimembranosus (SM) muscle early postmortem and at 1440 min, then compared these differences against biochemical and metabolic characteristics responsible for pork quality development. Color (L*, a*) differed (P < 0.001) by zone and time but no interaction was evident. Lactate content and pH were highly correlated (R² = 0.92) at 30 min, but weakened (R² = 0.161412) by 1440 min. Lactate anaplerosis was not responsible for this lack of relationship. Glycolytic potential also differed across zone (P < 0.001) and time (P < 0.005). Differences in myoglobin expression and abundance, as well as mitochondrial DNA were notable (P < 0.05) across zone. These data suggest inherent differences in SM muscle are key determinants of ham color variation, while postmortem metabolism may play a lesser role in driving this quality attribute.

Rhabdomyolysis: A syndrome to be considered

Rhabdomyolysis is characterized by the release of intracellular elements after the destruction of skeletal muscle. Is characterized by the presence of muscle pain, weakness, and dark urine, associated with elevated creatine kinase (CK). The causes related to this syndrome are varied, being traumatic etiology, immobilization, sepsis, drugs and alcohol the most frequent. CK values are used for diagnosis and prognosis, being renal dysfunction the most serious complication. Treatment is based on early and intensive fluid therapy to avoid kidney complications.

Myoglobin, expressed in brown adipose tissue of mice, regulates the content and activity of mitochondria and lipid droplets

The identification of novel physiological regulators that stimulate energy expenditure through brown adipose tissue (BAT) activity in substrate catalysis is of utmost importance to understand and treat metabolic diseases. Myoglobin (MB), known to store or transport oxygen in heart and skeletal muscles, has recently been found to bind fatty acids with physiological constants in its oxygenated form (i.e., MBO2). Here, we investigated the in vivo effect of MB expression on BAT activity. In particular, we studied mitochondrial function and lipid metabolism as essential determinants of energy expenditure in this tissue. We show in a MB-null (MBko) mouse model that MB expression in BAT impacts on the activity of brown adipocytes in a twofold manner: i) by elevating mitochondrial density plus maximal respiration capacity, and through that, by stimulating BAT oxidative metabolism along with the organelles` uncoupled respiration; and ii) by influencing the free fatty acids pool towards a palmitate-enriched composition and shifting the lipid droplet (LD) equilibrium towards higher counts of smaller droplets. These metabolic changes were accompanied by the up-regulated expression of thermogenesis markers UCP1, CIDEA, CIDEC, PGC1-α and PPAR-α in the BAT of MB wildtype (MBwt) mice. Along with the emergence of the "browning" BAT morphology, MBwt mice exhibited a leaner phenotype when compared to MBko littermates at 20 weeks of age. Our data shed novel insights into MB's role in linking oxygen and lipid-based thermogenic metabolism. The findings suggest potential new strategies of targeting the MB pathway to treat metabolic disorders related to diminishing energy expenditure.

Conformational dynamics of myoglobin in the presence of vitamin B12: A spectroscopic and in silico investigation

Myoglobin is an essential transport protein of heart and muscle tissues that acts as a local oxygen reservoir and a marker in different diseased conditions. On the other hand, Vitamin B12 is a vital nutrient that helps synthesize red blood cells, DNA, and proteins. To understand the ability of vitamin B12 to bind to the excess of myoglobin produced in the body under certain conditions (muscle injuries, severe trauma, etc.), it is essential to dig into the interaction between them. Therefore, the present study reports the binding interaction of vitamin B12 and myoglobin employing different spectroscopic and computational methods. The myoglobin's intrinsic fluorescence is quenched by vitamin B12 via static nature as observed from steady-state as well as time-resolved fluorescence measurements. The microenvironment of myoglobin's tryptophan residue gets affected, but there is no change observed in its α-helical content by vitamin B12 as seen from synchronous fluorescence and circular dichroism measurements. The probable binding of vitamin B12 on myoglobin was elucidated through molecular docking, and the interaction stability was studied by molecular dynamics simulation. The determination of vitamin B12's affinity to myoglobin and its effect on the conformational transitions of myoglobin might afford valuable insight for clinical pharmacology.

Impact of Conformational Substates and Energy Landscapes on Understanding Hemoglobin Kinetics and Function

Hans Frauenfelder's discovery of conformational substates in studies of myoglobin carbon monoxide geminate rebinding kinetics at cryogenic temperatures (Austin RH, Beeson KW, Eisenstein L, Frauenfelder H, & Gunsalus IC (1975) Dynamics of Ligand Binding to Myoglobin. Biochemistry 14(24):5355-5373) followed by his introduction of energy landscape theory with Peter Wolynes (Frauenfelder H, Sligar SG, & Wolynes PG (1991) The Energy Landscapes and Motions of Proteins. Science 254(5038):1598-1603) marked the beginning of a new era in the physics and physical chemistry of proteins. Their work played a major role in demonstrating the power and importance of dynamics and of Kramers reaction rate theory for understanding protein function. The biggest impact of energy landscape theory has been in the protein folding field, which is well-known and has been documented in numerous articles and reviews, including a recent one of my own (Eaton WA (2021) Modern Kinetics and Mechanism of Protein Folding: a Retrospective. J. Phys. Chem. B. 125(14):3452-3467). Here I will describe the much less well-known impact of their modern view of proteins on both experimental and theoretical studies of hemoglobin kinetics and function. I will first describe how Frauenfelder's experiments motivated and influenced my own research on myoglobin, which were key ingredients to my work on understanding hemoglobin.

Fluoride binding to characteristic heme-pocket centers: Insights into ligand stability

The studies on the L. pectinata hemoglobins (HbI, HbII, and HbIII) are essential because of their biological roles in hydrogen sulfide transport and metabolism. Variation in the pH could also play a role in the transport of hydrogen sulfide by HbI and oxygen by HbII and HbIII, respectively. Here, fluoride binding was used to further understand the structural properties essential for the molecular mechanism of ligand stabilization as a function of pH. The data allowed us to gain insights into how the physiological roles of HbI, HbII, HbIII, adult hemoglobin (A-Hb), and horse heart myoglobin (Mb) have an impact on the heme-bound fluoride stabilization. In addition, analysis of the vibrational assignments of the met-cyano heme complexes shows varied strength interactions of the heme-bound ligand. The heme pocket composition properties differ between HbI (GlnE7 and PheB10) and HbII/HbIII (GlnE7 and TyrB10). Also, the structural GlnE7 stereo orientation changes between HbI and HbII/HbIII. In HbI, its carbonyl group orients towards the heme iron, while in HbII/HbIII, the amino group occupies this position. Therefore, in HbI, the interactions to the heme-bound fluoride ion, cyanide, and oxygen with GlnE7 via H-bonding are not probable. Still, the aromatic cage PheB10, PheCD1, and PheE11 may contribute to the observed stabilization. However, a robust H-bonding networking stabilizes HbII and HbIII, heme-bound fluoride, cyanide, and oxygen ligand with the OH and NH2 groups of TyrB10 and GlnE7, respectively. At the same time, A-Hb and Mb have moderate but similar ligand interactions controlled by their respective distal E7 histidine.

Influence of heme propionates on the nitrite reductase activity of myoglobin

The heme propionates in myoglobin (Mb) form a H-bonding network among several residues within its second-sphere coordination, providing a key structural role towards Mb's functional properties. Our work aims to understand the role of the heme propionates on the nitrite reductase (NiR) activity (e.g. reduction of NO₂^- to NO) of this globin by studying an artificial dimethylester heme-substituted horse heart Mb (DME-Mb). The minor structural change brought about by esterification of the heme propionates causes the NiR rate to increase by more than over two-fold (5.6 ± 0.1 M^-1 s^-1) relative to wildtype (wt) Mb (2.3 ± 0.1 M^-1 s^-1). The lower pK_a observed in DME-Mb may enhance the tendency of His64 towards protonation, therefore increasing the NiR rate. In addition, the nitrite binding constant (K_nitrite) for DME-Mb^III is greater than wt Mb^III (350 M^-1 versus 120 M^-1). The disparity in the NiR activity correlates with the differences in electrostatic behavior, which influences the system's reactivity towards the approaching NO₂^- ion, and thus the formation of the Fe^II-NO₂^- intermediate.

Evaluating the failure to bloom in dark-cutting and lactate-enhanced beef longissimus steaks

Previous studies have noted lower L* (lightness) values for both dark-cutting beef and normal-pH beef enhanced with lactate. In the current study, absorption-coefficient, scattering-coefficient, CIE L*a*b* values, refractive index of sarcoplasm, and inter-muscle bundle space were evaluated for dark-cutting beef, normal-pH beef enhanced with lactate, normal-pH beef enhanced with water, and normal-pH beef not enhanced with either water or lactate. Compared with non-enhanced loins, lactate-enhancement had lower a*, chroma, oxymyoglobin, reflectance, scattering, and inter-muscle bundle space as well as greater absorption and refractive index. Dark-cutting steaks had lower a*, chroma, oxymyoglobin values, reflectance, and scattering as well as less inter-muscle bundle space compared with lactate-enhanced steaks. Sarcoplasm refractive index values were greater in lactate-enhanced steaks than dark-cutting steaks. The results suggest that changes in muscle structure and optical properties due to either pH or lactate addition can alter muscle darkening and blooming properties.

The peroxidatic activities of Myoglobin and Hemoglobin, their pathological consequences and possible medical interventions

Under those pathological conditions in which Myoglobin and Hemoglobin escape their cellular environments and are thus separated from cellular reductive/protective systems, the inherent peroxidase activities of these proteins can be expressed. This activity leads to the formation of the highly oxidizing oxo-ferryl species. Evidence that this happens in vivo is provided by the formation of a covalent bond between the heme group and the protein and this acts as an unambiguous biomarker for the presence of the oxo ferryl form. The peroxidatic activity also leads to the oxidation of lipids, the products of which can be powerful vasoconstrictive agents (e.g. isoprostanes, neuroprostanes). Here we review the evidence that lipid oxidation occurs following rhabdomyolysis and sub-arachnoid hemorrhage and that the products formed from arachidonic acid chains of phospholipids lead, through vasoconstriction, to kidney failure and brain vasospasm. Intervention in these pathological conditions through administration of reducing agents to remove ferryl heme is discussed. Through-protein electron transfer pathways that facilitate ferryl reduction at low reductant concentration have been identified. We conclude with consideration of the therapeutic use of Hemoglobin Based Oxygen carriers and how the toxicity of these may be reduced by engineering such electron transfer pathways into hemoglobin.

Forced running-induced rhabdomyolysis in the Sprague-Dawley rat: towards a rodent model of capture myopathy

Capture myopathy (CM) is a metabolic disease associated with mortality in mass boma captured (MBC) wildlife. The condition is induced by the forced pursuit, capturing, and restraint of wild animals, although its causal biology remains to be confirmed. A core feature of MBC-CM is rhabdomyolysis, which is associated with myoglobinuria and hyperthermia. Towards developing a translational model of CM-associated rhabdomyolysis, we investigated forced treadmill running to induce physical exhaustion and trigger rhabdomyolysis in Sprague Dawley (SD) rats. Twenty-four (24) SD rats (12 per sex) were subjected to treadmill habituation in a speed-tiered approach. Forty-eight hours after the last habituation session, one strenuous exercise (SE) session was performed at 75% of the theoretical VO_2MAX (30 m/min) until animals reached physical exhaustion. Core and skin surface temperatures were measured before the SE session and after rats reached exhaustion, after which a 1-h-cumulative urine sample was collected, and the myoglobin content assayed. We show that most SE, but not control-exposed (non-exercise) rats presented with myoglobinuria, while core and surface body temperatures in both male and female rats were significantly higher post-exercise. This pre-clinical model framework shows potential for investigating the pathophysiology of MBC-CM.

Admission serum myoglobin and the development of acute kidney injury after major trauma

BACKGROUND

Myoglobin and creatine kinase (CK) are both established markers of muscle injury but their hospital admission values have never been compared to predict post-traumatic acute kidney injury (AKI).

METHODS

An observational registry study of consecutive trauma patients admitted to a major regional trauma centre. The primary outcome was stage 1 or more AKI in the first 7 days after trauma. We assessed the association of hospital admission myoglobin or CK with development of AKI both alone and when added to two existing risk prediction models for post traumatic AKI.

RESULTS

Of the 857 trauma patients (median age 36 [25-52], 96% blunt trauma, median ISS of 20 [12-47]) included, 102 (12%) developed AKI. Admission myoglobin performed better than CK to predict AKI any stage with an AUC-ROC of 0.74 (95% CI 0.68-0.79) and 0.63 (95% CI 0.57-0.69), respectively (p < 0.001). Admission myoglobin also performed better than CK to predict AKI stage 2 or 3 [AUC-ROC of 0.79 (95% CI 0.74-0.84) and 0.74 (95% CI 0.69-0.79), respectively (p < 0.001)] with a best cutoff value of 1217 µg/L (sensitivity 74%, specificity 77%). Admission myoglobin added predictive value to two established models of AKI prediction and showed significant ability to reclassify subjects regarding AKI status, while admission CK did not. Decision curve analysis also revealed that myoglobin added net benefit to established predictive models. Admission myoglobin was better than CK at predicting development of significant rhabdomyolysis.

CONCLUSIONS

Admission myoglobin better predicts the development of AKI and severe rhabdomyolysis after major trauma. Admission myoglobin should be added in established predictive models of post-traumatic AKI to early identify high-risk patients.

Kinetic mechanisms for O2 binding to myoglobins and hemoglobins

Antonini and Brunori's 1971 book "Hemoglobin and Myoglobin in Their Reactions with Ligands" was a truly remarkable publication that summarized almost 100 years of research on O₂ binding to these globins. Over the ensuing 50 years, ultra-fast laser photolysis techniques, high-resolution and time resolved X-ray crystallography, molecular dynamics simulations, and libraries of recombinant myoglobin (Mb) and hemoglobin (Hb) variants have provided structural interpretations of O₂ binding to these proteins. The resultant mechanisms provide quantitative descriptions of the stereochemical factors that govern overall affinity, including proximal and distal steric restrictions that affect iron reactivity and favorable positive electrostatic interactions that preferentially stabilize bound O₂. The pathway for O₂ uptake and release by Mb and subunits of Hb has been mapped by screening libraries of site-directed mutants in laser photolysis experiments. O₂ enters mammalian Mb and the α and β subunits of human HbA through a channel created by upward and outward rotation of the distal His at the E7 helical position, is non-covalently captured in the interior of the distal cavity, and then internally forms a bond with the heme Fe(II) atom. O₂ dissociation is governed by disruption of hydrogen bonding interactions with His (E7), breakage of the Fe(II)-O₂ bond, and then competition between rebinding and escape through the E7-gate. The structural features that govern the rates of both the individual steps and overall reactions have been determined and provide the framework for: (1) defining the physiological functions of specific globins and their evolution; (2) understanding the clinical features of hemoglobinopathies; and (3) designing safer and more efficient acellular hemoglobin-based oxygen carriers (HBOCs) for transfusion therapy, organ preservation, and other commercially relevant O₂ transport and storage processes.

Myoglobin and troponin as prognostic factors in patients with COVID-19 pneumonia

BACKGROUND

The outbreak of novel coronavirus pneumonia 2019 (COVID-19) has caused millions of deaths worldwide. It is well documented that troponin predicts the prognosis of patients. Myoglobin is not only an important marker of myocardial injury, but it indicates systemic muscle damage. However, its relationship with COVID-19 was rarely reported. The present study compared the predictive value of troponin and myoglobin on the final prognosis of COVID-19 patients by analyzing the clinical characteristics and serum levels of myoglobin and troponin in severe/critical COVID-19 patients.

METHODS

We enrolled 499 consecutive eligible hospitalized patients with severe/critical COVID-19 from February 14 to March 24, 2020 at Leishenshan Hospital, Wuhan, China. Clinical characteristics and laboratory data were collected and compared between the patients who died and survived. We analyzed the receiver operating characteristic curves of myoglobin and troponin. Then, the patients were divided into myo⁺ group, myo^- group, tro⁺ group, and tro^- group, and survival curves were analyzed. The prognostic predictable values of myoglobin and troponin were further analyzed using Cox multifactorial analysis.

RESULTS

Myoglobin and troponin were significantly elevated in the death group (134.4 [interquartile range (IQR) 24.80, 605] vs 38.02 [IQR 3.87, 11.73]ng/ml, p<0.001), and troponin was also significantly elevated in the death group (0.01 [IQR 0.01, 0.01] vs 0.04 [IQR 0.02, 0.15]ng/ml, p<0.001). The ROC curves demonstrated that the area under the curve when using myoglobin to predict patient death was 0.911, with a threshold of 1.17, which was equivalent to troponin. Kaplan-Meier survival analysis revealed a significantly lower survival curve in the myo⁺ group than the myo^- group. Multifactor Cox survival analysis showed that troponin was no longer significant (HR=0.98, 95% CI 0.92-1.03, p=0.507), but elevated myoglobin was an independent predictor of death in COVID-19 patients (HR=1.001, 95% CI 1.001-1.002, p<0.001). The analysis of the Cox model for predicting patient death and plotting decision curves suggested that the single factor myoglobin model was superior to troponin, and the predictive value of the multifactor model was superior to the single-factor analyses.

CONCLUSIONS

In severe/critical COVID-19 patients, myoglobin and troponin were predictors of mortality and the probability of conversion to critical illness, and myoglobin may be superior to troponin for predictive value.

Myoglobin and troponin as prognostic factors in patients with COVID-19 pneumonia

Background

The outbreak of novel coronavirus pneumonia 2019 (COVID-19) has caused millions of deaths worldwide. It is well documented that troponin predicts the prognosis of patients. Myoglobin is not only an important marker of myocardial injury, but it indicates systemic muscle damage. However, its relationship with COVID-19 was rarely reported. The present study compared the predictive value of troponin and myoglobin on the final prognosis of COVID-19 patients by analyzing the clinical characteristics and serum levels of myoglobin and troponin in severe/critical COVID-19 patients.

Methods

We enrolled 499 consecutive eligible hospitalized patients with severe/critical COVID-19 from February 14 to March 24, 2020 at Leishenshan Hospital, Wuhan, China. Clinical characteristics and laboratory data were collected and compared between the patients who died and survived. We analyzed the receiver operating characteristic curves of myoglobin and troponin. Then, the patients were divided into myo⁺ group, myo^- group, tro⁺ group, and tro^- group, and survival curves were analyzed. The prognostic predictable values of myoglobin and troponin were further analyzed using Cox multifactorial analysis.

Results

Myoglobin and troponin were significantly elevated in the death group (134.4 [interquartile range (IQR) 24.80, 605] vs 38.02 [IQR 3.87, 11.73] ng/ml, p < 0.001), and troponin was also significantly elevated in the death group (0.01 [IQR 0.01, 0.01] vs 0.04 [IQR 0.02, 0.15] ng/ml, p < 0.001). The ROC curves demonstrated that the area under the curve when using myoglobin to predict patient death was 0.911, with a threshold of 1.17, which was equivalent to troponin. Kaplan-Meier survival analysis revealed a significantly lower survival curve in the myo⁺ group than the myo^- group. Multifactor Cox survival analysis showed that troponin was no longer significant (HR = 0.98, 95% CI 0.92-1.03, p = 0.507), but elevated myoglobin was an independent predictor of death in COVID-19 patients (HR = 1.001, 95% CI 1.001-1.002, p < 0.001). The analysis of the Cox model for predicting patient death and plotting decision curves suggested that the single factor myoglobin model was superior to troponin, and the predictive value of the multifactor model was superior to the single-factor analyses.

Conclusions

In severe/critical COVID-19 patients, myoglobin and troponin were predictors of mortality and the probability of conversion to critical illness, and myoglobin may be superior to troponin for predictive value.

A monocentric retrospective study

BACKGROUND

Limited data on myoglobin and infectious diseases are available. In this study, we evaluate the potential role of myoglobin in predicting poor outcome in patients with Sars-Cov2 pneumonia.

METHODS

One hundred and twenty-one Sars-Cov 2 patients with an average age of 69.9 ± 13.2 years, and symptoms duration of 8.8 ± 7.9 days were enrolled in the study. At the admission, the serum levels of myoglobin, erythrocyte sedimentation rate, C reactive protein (CRP), procalcitonin, ferritin, creatine phosphokinase, creatinine, fibrinogen, d-dimers, lactic dehydrogenase, troponin (Tn-I), creatine kinase myocardial band (CK-MB), complement fractions C3 and C4, immunoglobulins, interleukin 6 were evaluated. We also assessed the patients' complete clinical history and performed a thorough physical examination including age, disease history, and medications.

RESULTS

Twenty-four (20%) patients died, and 18 (15%) patients required intensive care. The mean time between symptoms onset and death was 12.4 days ± 9.1. Univariate analysis of the patients' data highlighted some independent risk factors for mortality in COVID-19, including higher neutrophils rate (HR: 1.171), lower lymphocyte rate (HR: 0.798), high CK-MB serum levels (HR: 1.6), high Tn-I serum levels (HR: 1.03), high myoglobin serum levels (HR: 1.014), Alzheimer (HR 5.8), and higher CRP values (HR: 1.011). Cox regression analysis model revealed that higher serum values of myoglobin (HR 1.003; 95%CI: 1.001-1.006; p = 0.01), and CRP (HR 1.012; 95% CI: 1.001-1.023; p = 0.035) could be predictors of mortality in COVID-19 patients. The value of the myoglobin level for predicting 28 days-mortality using ROC curve was 121.8 ng/dL. Lower survival rate was observed in patients with serum levels of myoglobin>121.8 ng/dL (84% vs 20% respectively, p = 0.0001).

CONCLUSION

Our results suggest that higher serum levels of myoglobin could be a considerable and effective predictor of poor outcomes in COVID-19 patients; a careful follow-up in these patients is strongly suggested. The possibility of enhancing these findings in other cohorts of COVID-19 patients could validate the clinical value of myoglobin as a biomarker for worse prognosis in COVID-19.

Free radical-mediated acetaldehyde formation by model reactions of dietary components: effects of meat, wine, cooking oil and coffee

Background

Alcohol consumption and the ingestion of red meat and oxidized cooking oil are risk factors of gastric and colorectal cancers. We reported that acetaldehyde (AcAld) is generated from Heme/Mb/Meat-Linoleate-EtOH model reaction mixtures, and thus could be a new plausible mechanism for the carcinogenesis (Kasai and Kawai, ACS Omega, 2021).

Results

In this study, we investigated the effects of wine and coffee, in addition to meat components, on this reaction. Depending on the conditions, such as pH, reaction time and choice of free hemin, myoglobin (Mb), as well as meat extracts (raw meat, baked meat, salami), wine and coffee enhanced AcAld formation. Polyphenols in red wine and coffee may stimulate AcAld formation by acting as pro-oxidants in the presence of Heme/Mb/Meat. In a model reaction of Mb + EtOH + H₂O₂, we observed time-dependent AcAld formation. In support of these in vitro data, after the consumption of a red meat-rich diet with red wine, the fecal AcAld level significantly increased as compared to the levels associated with a diet of fish + wine, or red meat without alcohol.

Conclusions

These results suggested that AcAld generation from dietary components may be an important mechanism of gastrointestinal tract carcinogenesis.

RIG-I, a novel DAMPs sensor for myoglobin activates NF-κB/caspase-3 signaling in CS-AKI model

BACKGROUND

Acute kidney injury (AKI) is the main life-threatening complication of crush syndrome (CS), and myoglobin is accepted as the main pathogenic factor. The pattern recognition receptor retinoicacid-inducible gene I (RIG-I) has been reported to exert anti-viral effects function in the innate immune response. However, it is not clear whether RIG-I plays a role in CS-AKI. The present research was carried out to explore the role of RIG-I in CS-AKI.

METHODS

Sprague-Dawley rats were randomly divided into two groups: the sham and CS groups (n = 12). After administration of anesthesia, the double hind limbs of rats in the CS group were put under a pressure of 3 kg for 16 h to mimic crush conditions. The rats in both groups were denied access to food and water. Rats were sacrificed at 12 h or 36 h after pressure was relieved. The successful establishment of the CS-AKI model was confirmed by serum biochemical analysis and renal histological examination. In addition, RNA sequencing was performed on rat kidney tissue to identify molecular pathways involved in CS-AKI. Furthermore, NRK-52E cells were treated with 200 μmol/L ferrous myoglobin to mimic CS-AKI at the cellular level. The cells and cell supernatant samples were collected at 6 h or 24 h. Small interfering RNAs (siRNA) was used to knock down RIG-I expression. The relative expression levels of molecules involved in the RIG-I pathway in rat kidney or cells samples were measured by quantitative Real-time PCR (qPCR), Western blotting analysis, and immunohistochemistry (IHC) staining. Tumor necrosis factor-α (TNF-α) was detected by ELISA. Co-Immunoprecipitation (Co-IP) assays were used to detect the interaction between RIG-I and myoglobin.

RESULTS

RNA sequencing of CS-AKI rat kidney tissue revealed that the different expression of RIG-I signaling pathway. qPCR, Western blotting, and IHC assays showed that RIG-I, nuclear factor kappa-B (NF-κB) P65, p-P65, and the apoptotic marker caspase-3 and cleaved caspase-3 were up-regulated in the CS group (P < 0.05). However, the levels of interferon regulatory factor 3 (IRF3), p-IRF3 and the antiviral factor interferon-beta (IFN-β) showed no significant changes between the sham and CS groups. Co-IP assays showed the interaction between RIG-I and myoglobin in the kidneys of the CS group. Depletion of RIG-I could alleviate the myoglobin induced expression of apoptosis-associated molecules via the NF-κB/caspase-3 axis.

CONCLUSION

RIG-I is a novel damage-associated molecular patterns (DAMPs) sensor for myoglobin and participates in the NF-κB/caspase-3 signaling pathway in CS-AKI. In the development of CS-AKI, specific intervention in the RIG-I pathway might be a potential therapeutic strategy for CS-AKI.

Changes in the structure and digestibility of myoglobin treated with sodium chloride

Myoglobin is a protein not easily broken down by digestive enzymes due to its rigid structure. This study evaluated the structural characteristics of myoglobin under various sodium chloride treatments (0.4-0.8 mol/L for 5-10 h) and the impacts on its digestibility using spectroscopic and molecular dynamics simulation techniques. Myoglobin digestibility was 40% following pepsin digestion and 60% after being sequentially digested by pepsin and trypsin. The α-helix content of myoglobin did not change significantly following sodium chloride treatment but hydrophobic amino acids were exposed and the binding of phenylalanine targeted by some digestive enzymes became more stable, leading to the reduced digestibility.

Microcapillary-based multicolor assay for quantitative and sensitive point-of-care testing of proteins

A microcapillary-based multicolor assay was developed for proteins quantification in serum sample with the assistance of manual centrifugal platform. The proposed assay only required the operation of "one suction and one extrusion" to realize the target detection. Myoglobin (Myo), a biomarker in the early stage of acute myocardial infarction (AMI), was chosen as the model target. The microcapillary was first modified with polydopamine (PDA), then Myo aptamer was immobilized on the PDA modified microcapillary and hybridized with glucose oxidase (Gox) functionalized DNA probe (DNA-Gox). The step "one suction" referred to the inhalation of the sample into the functionalized microcapillary. Then the target Myo in the sample could bind to the Myo aptamer on the microcapillary so that DNA-Gox complexes were released from the microcapillary into solution. Through the step "one extrusion", the DNA-Gox complexes in the solution could catalyze glucose to generate hydrogen peroxide, and then the etching of gold nanorods (AuNRs) was initiated, causing a color change from brown to yellow. According to the color change based on the etching of AuNRs, as low as 0.1 nM Myo was detected with naked eyes. Combined with the manual centrifugal platform, even the Myo in the serum samples could be detected without power supply. It was expected to build a universal and adaptable sensing platform for different targets more quickly and efficiently.

Ca2+ as activator of pseudoperoxidase activity of pigeon, Eurasian woodcock and chicken myoglobins: New features for meat preservation studies

Myoglobin (Mb), hemeprotein that binds dioxygen in muscle, affects meat colour. Moreover, in presence of peroxides, metMb is a potent oxidant involved in oxidative rancidity in meat. Here, following pigeon Mb purification and primary structure mass spectroscopy characterization, we determined its autoxidation rate and pseudoperoxidase activity with respect to chicken and E. woodcock Mbs. The three Mbs exhibit different autoxidation rates (0.153-h^-1 pigeon, 0.194-h^-1 chicken and 0.220-h^-1 E. woodcock Mbs) and similar specificity constant (9.86x10³ M^-1s^-1 pigeon, 8.81x10³ M^-1s^-1 chicken and 9.90x10³ M^-1s^-1 E. woodcock Mbs), considering their pseudoperoxidase activity. Moreover, for the first time, we detected an increase in pseudoperoxidase activity in presence of Ca²⁺, particularly at pH 5.8. NMR and CD data indicate that the nonspecific Ca²⁺ binding induces small local structural rearrangements that in turn slightly reduce pigeon Mb thermal stability. However, considering Ca²⁺ concentration variations before and post-mortem, this finding must be considered for meat preservation.

Effects of zinc binding on the binding of epigallocatechin gallate (green tea) to bovine serum albumin and myoglobin

Serum albumin as a zinc carrier binds 80% plasma zinc to facilitate zinc absorption. Epigallocatechin gallate (EGCG, green tea) is reported to bind to serum albumin to perform its biological functions in vivo. However, the available information on how zinc binding affects the binding of EGCG to proteins or how EGCG binding affects the binding of zinc to proteins are very limited. In the present study, the effects of zinc binding on the binding of EGCG to bovine serum albumin and myoglobin were investigated using isothermal titration calorimetry, fluorescence quenching and molecular docking. The obtained results suggested that binding of zinc to bovine serum albumin and myoglobin could increase the EGCG binding affinity of proteins as indicated by the thermodynamic parameters. In addition, the formation of protein/zinc complex shifted the EGCG binding site of proteins. For myoglobin, the electron transfer from EGCG to myoglobin was facilitated by zinc binding induced stronger EGCG binding to myoglobin. Such study provides very fundamental and useful knowledge for zinc and EGCG nutrition.

Thermal denaturation and autoxidation profiles of carangid fish myoglobins

Although myoglobin (Mb) has been considered to be one of the well-characterized proteins, screening of post-genomic era databases revealed the lack of adequate information on teleost Mbs. The present study was aimed to investigate stability and functional features of Mbs from three teleosts of the same family. To unfold how primary structure influences the stability and function of proteins, Mbs were purified from the dark muscles of three carangids, namely, yellowtail, greater amberjack, and silver trevally. Thermostabilities measured by circular dichroism (CD) spectrometry revealed species-specific thermal denaturation pattern, i.e., silver trevally > yellowtail > greater amberjack Mbs. On the other hand, autoxidation rate constants of the ferrous forms of those three carangid Mbs showed positive correlation between the ferrous state of the heme iron and rising temperature. The order of autoxidation rate was in the order of greater amberjack > yellowtail > silver trevally Mbs. The finding of the present study denotes that the thermal stability is not necessarily correlated with the functional stability of carangid Mbs even though their primary structures shared high homology (84-94%).

Allostery: The Rebound of Proteins

The discovery of hemoglobin allosteric properties is briefly summarized and contextualized in the frame of the main biochemical revelations that characterized the first half of the XX century. In particular, the historical background of DNA, RNA, and protein structure research is recalled and the new role that protein-protein interaction may have on allosteric regulation is discussed.

Repurposing metalloproteins as mimics of natural metalloenzymes for small-molecule activation

Artificial metalloenzymes (ArMs) consist of an unnatural metal or cofactor embedded in a protein scaffold, and are an excellent platform for applying the concepts of protein engineering to catalysis. In this Focused Review, we describe the application of ArMs as simple, tunable artificial models of the active sites of complex natural metalloenzymes for small-molecule activation. In this sense, ArMs expand the strategies of synthetic model chemistry to protein-based supporting ligands with potential for participation from the second coordination sphere. We focus specifically on ArMs that are structural, spectroscopic, and functional models of enzymes for activation of small molecules like CO, CO₂, O₂, N₂, and NO, as well as production/consumption of H₂. These ArMs give insight into the identities and roles of metalloenzyme structural features within and near the cofactor. We give examples of ArM work relevant to hydrogenases, acetyl-coenzyme A synthase, superoxide dismutase, heme oxygenases, nitric oxide reductase, methyl-coenzyme M reductase, copper-O₂ enzymes, and nitrogenases.

The Use of Supra-Hemodiafiltration in Traumatic Rhabdomyolysis and Acute Kidney Injury: A Case Report

Oliguric acute kidney injury due to traumatic rhabdomyolysis can be potentially lethal if the proper medical therapy combined with extracorporeal detoxification is not performed. Different extracorporeal techniques are available to overcome this syndrome. Here, we report the first case of removal of myoglobin and successful recovery from acute kidney injury in an elderly septic patient using supra-hemodiafiltration with endogenous reinfusion technique (HFR-Supra) combined with the medical therapy.

Impact of denaturing agents on surface properties of myoglobin solutions

The addition of denaturants strongly influences the surface properties of aqueous myoglobin solutions. The effect differs from the results for mixed solutions of the denaturants and other globular proteins, for example, bovine serum albumin (BSA), lysozyme and β-lactoglobulin (BLG), although the surface properties of the solutions of the pure proteins are similar. The kinetic dependencies of the dynamic surface elasticity of myoglobin solutions with guanidine hydrochloride (GuHCl) reveal at least two adsorption steps at denaturant concentrations higher than 1 M: a very fast increase of the dynamic surface elasticity to approximately 30 mN/m at the beginning of adsorption, and a slower growth to abnormally high values of 250-300 mN/m. At the same time, the surface elasticity of BSA/GuHCl, BLG/GuHCl and lysozyme/GuHCl solutions is a non-monotonic function of the surface age, and does not exceed 50 mN/m close to equilibrium. The high surface elasticity of myoglobin/GuHCl solutions may be associated with protein aggregation in the surface layer. The formation of aggregates is confirmed by ellipsometry and Brewster angle microscopy. The addition of ionic surfactants to protein solutions leads to the formation of myoglobin/surfactant complexes, and the kinetic dependencies of the dynamic surface elasticity display local maxima indicating multistep adsorption kinetics, unlike the corresponding results for solutions of other globular proteins mixed with ionic surfactants. Ellipsometry and infrared reflection-absorption spectroscopy allow tracing the adsorption of the complexes and their displacement from the interface at high surfactant concentrations.

Effects of temperature and relative humidity in D2O on solid-state hydrogen deuterium exchange mass spectrometry (ssHDX-MS)

Lyophilized powders containing myoglobin and various excipients were subjected to ssHDX-MS at different temperatures and D₂O vapor activity (RH). Deuterium incorporation was fitted to a bi-exponential association model for each formulation and the dependence of regression parameters on temperature and RH was evaluated. Data fitted best to a simplified model in which the slow exponential term was considered invariant with temperature and RH while the fast exponential term retained its temperature and RH dependence. This suggests that rapid rate processes such as water vapor sorption and initial deuterium labeling may be more dependent on temperature and RH than slower processes such as sequential exchange and transport in the solid matrix.

Rapid and non-destructive spectroscopic method for classifying beef freshness using a deep spectral network fused with myoglobin information

A simple, novel, rapid, and non-destructive spectroscopic method that employs the deep spectral network for beef-freshness classification was developed. The deep-learning-based model classified beef freshness by learning myoglobin information and reflectance spectra over different freshness states. The reflectance spectra (480-920 nm) were measured from 78 beef samples for 17 days, and the datasets were sorted into three freshness classes based on their pH values. Myoglobin information showed statistically significant differences depending on the freshness; consequently, it was utilized as a crucial parameter for classification. The model exhibited improved performance when the reflectance spectra were combined with the myoglobin information. The accuracy of the proposed model improved to 91.9%, whereas that of the single-spectra model was 83.6%. Further, a high value for the area under the receiver operating characteristic curve (0.958) was recorded. This study provides a basis for future studies on the investigation of myoglobin information associated with meat freshness.

[CME/Answers: Elevated Creatine Kinase as a Diagnostic Parameter of Rhabdomyolysis]

CME/Answers: Elevated Creatine Kinase as a Diagnostic Parameter of Rhabdomyolysis Abstract. Elevated CK values with or without symptoms require clarification in order to rule out possible secondary complications. Adequate hydrogenation, discontinuation of possibly triggering drugs and noxious agents, and close laboratory controls are decisive for the outcome. Acute rhabdomyolysis can have various causes, which can generally be classified as traumatic or atraumatic. In case of recurrent occurrence, genetic or autoimmunological diseases must also be excluded. In addition to a detailed anamnesis, physical examination, laboratory and urine tests, a variety of diagnostic methods are available, which should be used selectively. The aim of this work is to address possible clarification strategies, causes and differential diagnoses of an increase in creatine kinase and rhabdomyolysis. We illustrate these with a case.

Blood purification with a cytokine adsorber for the elimination of myoglobin in critically ill patients with severe rhabdomyolysis

BACKGROUND

Rhabdomyolysis is frequently occurring in critically ill patients, resulting in a high risk of acute kidney injury (AKI) and potentially permanent kidney damage due to increased myoglobin levels. The extracorporeal elimination of myoglobin might be an approach to prevent AKI, but its molecular weight of 17 kDa complicates an elimination with conventional dialysis membranes. Question of interest is, if myoglobin can be successfully eliminated with the cytokine adsorber Cytosorb® (CS) integrated in a high-flux dialysis system.

METHODS

Patients were included between 10/2014 and 05/2020 in the study population if they had an anuric renal failure with the need of renal replacement therapy, if CS therapy was longer than 90 min and if myoglobin level was > 5.000 ng/ml before treatment. The measurement times of the laboratory values were: d-1 = 24-36 h before CS, d0 = shortly before starting CS and d1 = 12-24 h after starting CS treatment. Statistical analysis were performed with Spearman's correlation coefficient, Wilcoxon test with associated samples and linear regression analysis.

RESULTS

Forty-three patients were included in the evaluation (median age: 56 years, 77% male patients, 32.6% ECMO therapy, median SAPS II: 80 points and in-hospital mortality: 67%). There was a significant equilateral correlation between creatine kinase (CK) and myoglobin at all measurement points. Furthermore, there was a significant reduction of myoglobin (p = 0.03, 95% confidence interval (CI): - 9030, - 908 ng/ml) during CS treatment, with a median relative reduction of 29%. A higher median reduction of 38% was seen in patients without ongoing rhabdomyolysis (CK decreased during CS treatment, n = 21). In contrast, myoglobin levels did not relevantly change in patients with increasing CK and therefore ongoing rhabdomyolysis (n = 22, median relative reduction 4%). Moreover, there was no significant difference in myoglobin elimination in patients with and without ECMO therapy.

CONCLUSION

Blood purification with Cytosorb® during high-flux dialysis led to a significant reduction of myoglobin in patients with severe rhabdomyolysis. The effect might be obscured by sustained rhabdomyolysis, which was seen in patients with rising CK during treatment. Prospective clinical trials would be useful in investigating its benefits in avoiding permanent kidney damage.