Exploring the interaction mechanism of chlorogenic acid and myoglobin: Insights from structure and molecular dynamics simulation.

This study focused on non-covalent complex of myoglobin-chlorogenic acid (Mb-CA) and the changes in conformation, oxidation, and microstructure induced by varying concentrations of CA (10-40 µmol/g Mb). Employing molecular docking and dynamics simulations, further insights into the interaction between Mb and CA were obtained. The findings revealed that different CA concentrations enhanced Mb's thermal stability, while diminishing particle size, solubility, and relative content of metmyoglobin (MetMb%). The optimal interaction occurred at 40 µmol/g Mb. Furthermore, CA exhibited static quenching of Mb, with thermodynamic analysis confirming a 1:1 complex formation. These insights deepen our understanding of interaction between Mb and CA, providing valuable clarity.

Review of the Greening Reaction by Thermal Treatment: New Insights Exploring the Structural Implications of Myoglobin.

Myoglobin is the main factor responsible for muscle pigmentation in tuna; muscle color depends upon changes in the oxidative state of myoglobin. The tuna industry has reported muscle greening after thermal treatment involving metmyoglobin (MetMb), trimethylamine oxide (TMAO), and free cysteine (Cys). It has been proposed that this pigmentation change is due to a disulfide bond between a unique cysteine residue (Cys10) found in tuna MetMb and free Cys. However, no evidence has been given to confirm that this reaction occurs. In this review, new findings about the mechanism of this greening reaction are discussed, showing evidence of how free radicals produced from Cys oxidation under thermal treatment participate in the greening of tuna and horse muscle during thermal treatment. In addition, the reaction conditions are compared to other green myoglobins, such as sulfmyoglobin, verdomyoglobin, and cholemyoglobin.

Binding mechanism of disulfide species to ferric hemeproteins: The case of metmyoglobin.

The interactions of the heme iron of hemeproteins with sulfide and disulfide compounds are of potential interest as physiological signaling processes. While the interaction with hydrogen sulfide has been described computationally and experimentally, the reaction with disulfide, and specifically the molecular mechanism for ligand binding has not been studied in detail. In this work, we study the association process for disulfane and its conjugate base disulfanide at different pH conditions. Additionally, by means of advanced sampling techniques based on multiple steered molecular dynamics, we provide free energy profiles for ligand migration for both acid/base species, showing a similar behavior to the previously reported for the related H2S/HS¯ pair. Finally, we studied the ligand interchange reaction (H2O/H2S, HS¯ and H2O/HSSH, HSS¯) by means of hybrid quantum mechanics-molecular mechanics calculations. We show that the anionic species are able to displace more efficiently the H2O bound to the iron, and that the H-bond network in the distal cavity can help the neutral species to perform the reaction. Altogether, we provide a molecular explanation for the experimental information and show that the global association process depends on a fine balance between the migration towards the active site and the ligand interchange reaction.

Autocatalytic Mechanism in the Anaerobic Reduction of Metmyoglobin by Sulfide Species.

The mechanism of the metal centered reduction of metmyoglobin (MbFeIII) by sulfide species (H2S/HS-) under an argon atmosphere has been studied by a combination of spectroscopic, kinetic, and computational methods. Asymmetric S-shaped time-traces for the formation of MbFeII at varying ratios of excess sulfide were observed at pH 5.3 < pH < 8.0 and 25 °C, suggesting an autocatalytic reaction mechanism. An increased rate at more alkaline pHs points to HS- as relevant reactive species for the reduction. The formation of the sulfanyl radical (HS•) in the slow initial phase was assessed using the spin-trap phenyl N-tert-butyl nitrone. This radical initiates the formation of S-S reactive species as disulfanuidyl/ disulfanudi-idyl radical anions and disulfide (HSSH•-/HSS•2- and HSS-, respectively). The autocatalysis has been ascribed to HSS-, formed after HSSH•-/HSS•2- disproportionation, which behaves as a fast reductant toward the intermediate complex MbFeIII(HS-). We propose a reaction mechanism for the sulfide-mediated reduction of metmyoglobin where only ferric heme iron initiates the oxidation of sulfide species. Beside the chemical interest, this insight into the MbFeIII/sulfide reaction under an argon atmosphere is relevant for the interpretation of biochemical aspects of ectopic myoglobins found on hypoxic tissues toward reactive sulfur species.

Reduction of metmyoglobin by inorganic disulfide species.

The mechanism of the metal centered reduction of metmyoglobin (MbFeIII) by inorganic disulfide species has been studied by combined spectroscopic and kinetic analyses, under argon atmosphere. The process is kinetically characterized by biexponential time traces, for variable ratios of excess disulfide to protein, in the pH interval 6.6-8.0. Using UV-vis and resonance Raman spectroscopies, we observed that MbFeIII is converted into a low spin hexacoordinated ferric complex, tentatively assigned as MbFeIII(HSS-)/MbFeIII(SS2-), in an initial fast step. The complex is slowly converted into a pentacoordinated ferrous form, assigned as MbFeII according to the resonance Raman records. The reduction is a pH-dependent process, but independent of the initial disulfide concentration, suggesting the unimolecular decomposition of the intermediate complex following a reductive homolysis. We estimated the rate of the fast formation of the complex at pH 7.4 (kon = 3.7 × 103 M-1 s-1), and a pKa2 = 7.5 for the equilibrium MbFeIII(HSS-)/MbFeIII(SS2-). Also, we estimated the rate for the slow reduction at the same pH (kred = 10-2 s-1). A reaction mechanism compliant with the experimental results is proposed. This mechanistic study provides a differential kinetic signature for the reactions of disulfide compared to sulfide species on metmyoglobin, which may be considered in other hemeprotein systems.

Integrative proteomics and metabolomics profiling to understand the biochemical basis of beef muscle darkening at a slightly elevated pH.

Previous studies investigated the biochemical basis of dark-cutting conditions at elevated muscle pH (above 6), but the molecular basis at slightly above normal pH (between 5.6 and 5.8) is still unclear. The objective was to determine protein and metabolite profiles to elucidate postmortem muscle darkening at slightly elevated pH. Loins were selected based on the criteria established in our laboratory before sample collections, such as pH less than 5.8, L* values (muscle lightness) less than 38, and not discounted by the grader (high-pH beef with dark color are discounted and not sold in retail stores). Six bright red loins (longissimus lumborum) at normal-pH (average pH = 5.57) and six dark-colored strip loins at slightly elevated pH (average pH = 5.70) from A maturity carcasses were obtained within 72-h postmortem from a commercial beef purveyor. Surface color, oxygen consumption, metmyoglobin reducing activity, protein, and metabolite profiles were determined on normal-pH and dark-colored steaks at slightly elevated pH. Enzymes related to glycogen metabolism and glycolytic pathways were more differently abundant than metabolites associated with these pathways. The results indicated that oxygen consumption and metmyoglobin reducing activity were greater (P < 0.05) in darker steaks than normal-pH steaks. Enzymes involved with glycogen catabolic pathways and glycogen storage disease showed lower abundance in dark beef. The tricarboxylic acid metabolite, aconitic acid, was overabundant in darker-colored beef than normal-pH beef, but glucose derivative metabolites were less abundant. The majority of glycogenolytic proteins and metabolites reported as overabundant in the previous dark-cutting studies at high pH (>6.4) also did not show significant differences in the current study. Therefore, our data suggest enzymes involved in glycogen metabolism, in part, create a threshold for muscle darkening than metabolites.

A bright cherry-red color beef is ideal during meat retail and carcass grading. Any deviation from a bright red color, such as dark red color, at the interface of the 12th and 13th rib-eye area leads to carcass discounts. Various studies have determined protein, metabolite, and mitochondrial profiles to understand the biochemical basis of dark-cutting beef (muscle pH greater than 6); however, limited knowledge is currently available on muscle darkening at a slightly elevated pH. Bright red loins at normal muscle pH and darker color loins at slightly elevated pH (not discounted by a grader) were collected 72-h postmortem from a commercial beef purveyor. Surface color, oxygen consumption, metmyoglobin reducing activity, protein, and metabolite profiles were determined on normal-pH and dark-colored steaks at slightly elevated pH. The results indicated that oxygen consumption and metmyoglobin reducing activity were greater in darker steaks than normal-pH steaks. Furthermore, the protein abundance profiles of enzymes related to glycogen metabolism and glycolytic pathways were more differently abundant than metabolites associated with these pathways. Understanding the factors involved in the occurrence of dark color steaks help to minimize losses due to discount carcasses.

Sulfmyoglobin production by free cysteine during thermal treatment: Involvement of heme iron in the production of free radicals.

The meat greening is an abnormal pigmentation related to microbiological contamination and lipid oxidation during storage. This color change results from sulfmyoglobin (SulfMb) production promoted by the reaction between metmyoglobin (MetMb), H2O2, and thiol compounds. Spectral studies on cooked meat suggested the production of SulfMb, probably due to the increment of free radicals during thermal treatment. Thus, we evaluated the involvement of free radicals and heme iron in the SulfMb production from horse MetMb and free cysteine (Cys) during thermal treatment. The results confirm that the reaction of SulfMb production at meat muscle pH (5.7-7.2) during heat treatment is a product of free radicals formed from Cys oxidation (SH) and reactive oxygen species (O2-, H2O2). This is catalyzed by the release of heme iron, thus promoting a consecutive reaction having MbFe(IV)O as a reaction intermediate.

Preliminary Investigation on the Relationship between Raman Spectra of Beef and Metmyoglobin and Metmyoglobin Reductase Activity.

A hand-held Raman spectroscopic device was used as a rapid nondestructive testing device to predict the metmyoglobin (MetMb) and metmyoglobin reductase activity (MRA) values on the surface layer of fresh beef. Longissimus dorsi muscles were from 10 young bulls (Holstein-Friesian) from two different cattle farms (group A = 5 and B = 5). The Raman spectra of 100 samples were correlated with the MetMb and MRA values using partial least squares regression (PLSR). Two groups could be discriminated, and the separate correlation models were better than the joint correlation model for the fresh beef. The coefficients of determination are R 2 = 0.81 (group A) and R 2 = 0.87 (group B) for MetMb and R 2 = 0.80 (group A) and R 2 = 0.85 (group B) for MRA. The results show the usefulness of Raman spectra in predicting the inner traits such as MetMb and MRA during meat storage. In conclusion, it is feasible to determine the MetMb and MRA values by Raman spectroscopy. Color is an important indicator of beef freshness and can vary depending on the age, sex, and breed of the cow. They play a very important role in human nutrition. The color of meat is an important indicator of meat freshness, and many researchers are already investigating the causes of color changes. The research was conducted in this environment.

The greening reaction of skipjack tuna (Katsuwonus pelamis) metmyoglobin promoted by free cysteine during thermal treatment.

Background: Tuna muscle greening is a problem that occurs after heating. A hypothesis has been postulated to address this problem, involving a conserved Cys residue at position 10 (Cys-10) present on tuna myoglobin (Mb) that is exposed during the thermic treatment, forming a disulfide bond with free cysteine (Cys) in the presence of trimethylamine oxide (TMAO), resulting in the greening of the tuna Mb. Methods: We present a study using skipjack tuna (Katsuwonus pelamis) metmyoglobin (MbFe(III)-H2O) where the effect of free Cys (1-6 mM), TMAO (1.33 mM), and catalase on the greening reaction (GR) was monitored by UV-vis spectrometry during thermal treatment at 60 °C for 30 min. Moreover, the participation of Cys-10 on the GR was evaluated after its blocking with N-ethymaleimide. Results: The GR occurred in tuna MbFe(III)-H2O after heat treatment with free Cys, forming sulfmyoglobin (MbFe(II)-S) as the responsible pigment for the tuna greening. However, the rate constants of MbFe(II)-S production depended on Cys concentration (up to 4 mM) and occurred regardless of the TMAO presence. We postulate that two consecutive reactions involve an intermediate ferrylmyoglobin (promoted by H2O2) species with a subsequent MbFe(II)-S formation since the presence of catalase fosters the reduction of the rate reaction. Moreover, GR occurred even with blocked Cys-10 residues in tuna Mb and horse Mb (without Cys in its sequence). Discussion: We found that GR is not exclusive to tuna Mb´s, and it can be promoted in other muscle systems. Moreover, Cys and thermal treatment are indispensable for promoting this pigmentation anomaly.

Effects of plasma activated solution on the colour and structure of metmyoglobin and oxymyoglobin.

Effects of plasma-activated solution (PAS) on the colour and structure of metmyoglobin (metMb) and oxymyoglobin (oxyMb) were investigated and the relationship between discolouration and structure changes was clarified for the first time. Results showed that the colour of PAS-treated metMb faded first, followed by green discolouration, while PAS-treated oxyMb turned from bright red to reddish-brown and then towards green in the end. It was due to the accumulation of H2O2, nitrite and nitrate in PAS with prolonging plasma treatment times. Also, the low concentrations of active species in PAS cannot influence the colour and structure of metMb and oxyMb. The accumulation of active species of H2O2 in PAS was the main reason for destructing myoglobin structure and transforming its colour with prolonging treatment time. Therefore, the concentration of H2O2 should be adjusted to a low level for treating red meats as their colour appearance is mainly determined by metMb and oxyMb.

Effect of squid pen chitooligosaccharide and epigallocatechin gallate on discoloration and shelf-life of yellowfin tuna slices during refrigerated storage.

This study evaluated the effects of treatments of squid pen chitooligosaccharide (COS) or epigallocatechin gallate (EGCG) or COS/EGCG mixture (1:1, w/w) at different concentrations (0, 200, and 400 mg/kg) on the discoloration and quality changes in yellowfin tuna slices stored at 4 °C for 12 days. Tuna slices added with 200 and 400 mg/kg of COS (C2 and C4, respectively) showed the lowest reduction in oxymyoglobin and a* value (redness) ascertained by the lower metmyoglobin formation than other samples. Additionally, C2 and C4 samples showed a lower total viable count and TBARS value than the remaining samples. EGCG alone and its mixture with COS exhibited lower efficacy in retaining the quality loss than COS alone. COS at both levels effectively reduced the metMb formation. It maintained the redness with sensory acceptability of slices up to 9 days, and C4 sample prolonged shelf-life for 12 days based on the microbiological limit.

Influence of the heme distal pocket on nitrite binding orientation and reactivity in Sperm Whale myoglobin.

Nitrite binding to recombinant wild-type Sperm Whale myoglobin (SWMb) was studied using a combination of spectroscopic methods including room-temperature magnetic circular dichroism. These revealed that the reactive species is free nitrous acid and the product of the reaction contains a nitrite ion bound to the ferric heme iron in the nitrito- (O-bound) orientation. This exists in a thermal equilibrium with a low-spin ground state and a high-spin excited state and is spectroscopically distinct from the purely low-spin nitro- (N-bound) species observed in the H64V SWMb variant. Substitution of the proximal heme ligand, histidine-93, with lysine yields a novel form of myoglobin (H93K) with enhanced reactivity towards nitrite. The nitrito-mode of binding to the ferric heme iron is retained in the H93K variant again as a thermal equilibrium of spin-states. This proximal substitution influences the heme distal pocket causing the pKa of the alkaline transition to be lowered relative to wild-type SWMb. This change in the environment of the distal pocket coupled with nitrito-binding is the most likely explanation for the 8-fold increase in the rate of nitrite reduction by H93K relative to WT SWMb.

X-ray-induced photoreduction of heme metal centers rapidly induces active-site perturbations in a protein-independent manner.

Since the advent of protein crystallography, atomic-level macromolecular structures have provided a basis to understand biological function. Enzymologists use detailed structural insights on ligand coordination, interatomic distances, and positioning of catalytic amino acids to rationalize the underlying electronic reaction mechanisms. Often the proteins in question catalyze redox reactions using metal cofactors that are explicitly intertwined with their function. In these cases, the exact nature of the coordination sphere and the oxidation state of the metal is of utmost importance. Unfortunately, the redox-active nature of metal cofactors makes them especially susceptible to photoreduction, meaning that information obtained by photoreducing X-ray sources about the environment of the cofactor is the least trustworthy part of the structure. In this work we directly compare the kinetics of photoreduction of six different heme protein crystal species by X-ray radiation. We show that a dose of ∼40 kilograys already yields 50% ferrous iron in a heme protein crystal. We also demonstrate that the kinetics of photoreduction are completely independent from variables unique to the different samples tested. The photoreduction-induced structural rearrangements around the metal cofactors have to be considered when biochemical data of ferric proteins are rationalized by constraints derived from crystal structures of reduced enzymes.

Impact of myoglobin oxygenation level on color stability of frozen beef steaks.

The emerging market of frozen meat emphasizes the need to better understand beef surface discoloration and the ideal parameters of freezing beef to retain an acceptable color. The objectives of this study were to determine the impacts of myoglobin oxygenation level prior to freezing and frozen storage duration on frozen beef color. USDA Choice strip loins (n = 36) were aged for 4 d or 20 d. Steaks were randomly assigned to a myoglobin oxygenation level [deoxygenated (DeOxy; immediately packaged after cutting), oxygenated (Oxy; oxygenated in air for 30 min), or highly oxygenated (HiOxy; packaged for 24 h in 80% O2)]. Steaks were then vacuum packaged in oxygen permeable or impermeable film and immediately frozen (-5 °C). Following either 0, 2, 4, or 6 mo of frozen storage, steaks were removed from the packaging and immediately analyzed for instrumental color (L*, a*, and b*), percent oxymyoglobin, metmyoglobin, and deoxymyoglobin, delta E, redness ratio, a*:b* ratio, hue angle, subjective discoloration, and lipid oxidation. The HiOxy steaks had greater oxygen penetration and the greatest a* values compared with DeOxy and Oxy steaks, regardless of packaging (P < 0.0005). With 4 d of aging, HiOxy steaks had greater a* values than DeOxy and Oxy at all storage times (P = 0.0118). The HiOxy steaks aged for 20 d and frozen for 6 mo had significantly higher delta E values than all other myoglobin oxygenation levels and postmortem aging periods (P < 0.0001). Redness and percent oxymyoglobin were highest for HiOxy steaks within each storage period (P < 0.0002). The HiOxy steaks had the highest percent oxymyoglobin and DeOxy had the lowest percent oxymyoglobin within each aging and storage period (P < 0.01). Conversely, DeOxy steaks had the highest percent metmyoglobin and HiOxy had the lowest percent metmyoglobin when packaged in impermeable film (P < 0.0001). The HiOxy steaks from 20 d of aging had the highest discoloration compared with 4 d aging and more discoloration than all other myoglobin treatments at 6 mo of storage (P < 0.0001). The HiOxy 20 d aged steaks exhibited the highest lipid oxidation values at 2, 4, and 6 mo (P = 0.0224) and HiOxy steaks exhibited a brighter and deeper cherry red color compared with the DeOxy steaks. The HiOxy steaks were greater in redness or similar when compared with Oxy steaks, but experienced more detrimental effects when frozen storage was extended.

Effects of iron-catalyzed and metmyoglobin oxidizing systems on biochemical properties of yak muscle myofibrillar protein.

The objective of this study was to compare the effects of two oxidation systems on the biochemical properties of yak myofibrillar protein (MP). Oxidation was induced by incubating MP with either an iron-catalyzed oxidizing system (IOS) or a metmyoglobin-oxidizing system (MOS). The following indicators of protein oxidation and protein degradation were analyzed. The carbonyl, disulfide bonds, dityrosine, and ß-sheet content increased markedly with oxidant concentration in both systems(P < .05), whereas the total sulfhydryl, surface hydrophobicity and α-helix content decreased significantly(P < .05). Furthermore, the MOS carbonyl formation rate was significantly faster than the IOS rate, and the MOS significantly affected the formation of disulfide bonds and inhibited the exposure of hydrophobic amino acids. Both oxidative systems promoted cross-linking of myosin heavy chains (MHCs) and action, but the degree of cross-linking in IOS was greater than that in MOS. MOS also promoted cross-linking of myosin light chains (MLCs). IOS and MOS produced mainly 20-25-kDa and 20-17-kDa MLC degradation products, respectively. In conclusion, oxidation caused cross-linking in MHCs or MLCs through disulfide bonds, but the extent of such cross-linking was oxidant dose-dependent and specific to each oxidizing system.

In Silico Insight into the Reductive Nitrosylation of Ferric Hemeproteins.

A combination of in silico methods was used to extend the experimental description of the reductive nitrosylation mechanism in ferric hemeproteins with the molecular details of the role of surrounding amino acids. The computational strategy consisted in the estimation of potential energy profiles for the transition process associated with the interactions of the coordinated N(NO) moiety with O(H2O) or O(OH-) as nucleophiles, and with distal amino acids as proton acceptors or affecting the stability of transition states. We inspected the reductive nitrosylation in three representative hemeproteins -sperm whale metmyoglobin, α subunit of human methemoglobin and nitrophorin 4 of Rhodnius prolixus. For each case, classical molecular dynamics simulations were performed in order to obtain relevant reactive conformations, and a potential energy profile for the reactive step was obtained using adiabatic mapping or nudged elastic band approaches at the QM/MM level. Specifically, we report the role of a charged Arg45 of myoglobin in destabilizing the transition state when H2O acts as nucleophile, differently to the neutral Pro43 of the hemoglobin subunit. The case of the nitrophorin is unique in that the access of the required water molecules is scarce, thus, preventing the reaction.

Cold non-enzymatic browning of glucosamine in the presence of metmyoglobin induces glucosone and deoxymyoglobin formation.

Glucosamine (GlcN) and GlcN-myoglobin reaction systems were incubated at 4 °C to verify that GlcN can go through non-enzymatic browning at this low temperature, and to test the hypothesis that certain reductones from GlcN non-enzymatic browning can promote the formation of deoxy- and oxymyoglobin from metmyoglobin reduction. Remarkably, alpha-dicarbonyls and self-condensation products, fructosazine and deoxyfructosazine, were produced at this relatively low temperature. The presence of myoglobin shifted GlcN non-enzymatic browning toward the formation of glucosone and fructosazine. When glucosone (250-2000 mg/L) was incubated with myoglobin it contributed to the formation of deoxymyoglobin, indicating its capacity to reduce metmyoglobin. This study opens the possibility of using GlcN in meat products to increase oxy- and deoxymyoglobin and enhance the color of meat.

Interrelationship between myoglobin oxidation and lipid oxidation during the processing of Cantonese sausage with d-sodium erythorbate.

BACKGROUND: Pork is used as raw material to produce Cantonese sausage, and 0.5 or 1 g kg-1 of d-sodium erythorbate is added to the pork meat. In this study the myoglobin oxidation rate, relative metmyoglobin content, heme iron content, redness, pH, free radical content and thiobarbituric acid reactive substance (TBARS) value were measured at different processing times and different content of d-sodium erythorbate. RESULTS: It was found that d-sodium erythorbate significantly reduced the free radical content and myoglobin and lipid oxidation rates and increased heme iron levels. When d-sodium erythorbate was added to the sausage, the absorption peak of myoglobin porphyrin shifted left, migrating from 414 to 405 nm. At 72 h, with an increase in the d-sodium erythorbate content, a significant negative correlation was identified between heme iron and the degree of redness (P < 0.01). CONCLUSION: During sausage processing, there are strong correlations among TBARS values, free radical content, metmyoglobin levels, heme iron levels, a* and pH at the same d-sodium erythorbate level. At the same processing time, adding d-sodium erythorbate can slow the rate of myoglobin and lipid oxidation and prevent the discoloration of sausage. © 2019 Society of Chemical Industry.

Carbon Chain Length of Lipid Oxidation Products Influence Lactate Dehydrogenase and NADH-Dependent Metmyoglobin Reductase Activity.

The biochemical basis of lower metmyoglobin reducing activity (MRA) in high-oxygen modified atmospheric packaged (HiOx-MAP) beef than those in vacuum and polyvinyl chloride (PVC) packaging is not clear. To explore this, the effects of lipid oxidation products with varying carbon chain length on lactate dehydrogenase (LDH) and NADH-dependent metmyoglobin reductase activity were evaluated. Surface color, MRA, and lipid oxidation of beef longissimus lumborum steaks (n = 10) were measured during 6-day display. Further, two enzymes, LDH and NADH-dependent metmyoglobin reductase (n = 5), critical for MRA were incubated with or without (control) lipid oxidation products of varying carbon chain length: malondialdehyde (3-carbon), hexenal (6-carbon), and 4-hydroxynonenal (9-carbon). Steaks in HiOx-MAP had greater (P < 0.05) redness than vacuum and PVC, but had lower (P < 0.05) MRA and greater (P < 0.05) lipid oxidation on day 6. LDH and NADH-dependent metmyoglobin reductase activities were differentially influenced by lipid oxidation products (P < 0.05). The results indicate that the difference in reactivity of various lipid oxidation products on LDH (HNE > MDA = hexenal) and NADH-dependent metmyoglobin reductase (HNE = MDA > hexenal) activity could be responsible for lower MRA in HiOx-MAP.

Effects of malondialdehyde as a byproduct of lipid oxidation on protein oxidation in rabbit meat.

The effects of malondialdehyde (MDA) as a byproduct of lipid oxidation on myoglobin and myofibrillar proteins (MP) oxidations in muscle homogenates containing components native to rabbit muscle were investigated. For myoglobin, MDA could lead to increase in metmyoglobin percentage. For MP, MDA could promote protein carbonylation and loss of tryptophan fluorescence. In addition, MDA could affect reactive oxygen species (ROS)-generating system by promoting the formation of hypervalent myoglobin species and release of non-heme iron. The result of MDA-MP adducts fluorescence intensity indicated that ROS-generating systems may be the main reason for protein carbonylation at the later of incubation treatment. SDS-PAGE analysis revealed that the ability of ROS-generating systems to facilitate protein oxidation was enhanced with MDA, which was responsible for the formation of protein cross-linking throughout incubation treatment. Taken together, the ability of MDA on promoting the oxidation of MP in rabbit muscle homogenates may be relied on both adduct reactions and the influence on ROS-generating system.