The objective of this study was to assess the morphological integrity and functional potential of mitochondria from postmortem bovine cardiac muscle and evaluate mitochondrial interactions with myoglobin (Mb) in vitro. Electron microscopy revealed that mitochondria maintained structural integrity at 2 h postmortem; prolonged storage resulted in swelling and breakage. At 2 h, 96 h, and 60 days postmortem, the mitochondrial state III oxygen consumption rate (OCR) and respiratory control ratio decreased with time at pH 7.2 and 5.6 (p < 0.05). Mitochondria isolated at 60 days did not exhibit ADP-induced transitions from state IV to state III oxygen consumption. Tissue oxygen consumption also decreased with time postmortem (p < 0.05). Mitochondrial oxygen consumption was inhibited by decreased pH in vitro (p < 0.05). In a closed system, mitochondrial respiration resulted in decreased oxygen partial pressure (pO(2)) and enhanced conversion of oxymyoglobin (OxyMb) to deoxymyoglobin (DeoMb) or metmyoglobin (MetMb). Greater mitochondrial densities caused rapid decreases in pO(2) and favored DeoMb formation at pH 7.2 in closed systems (p < 0.05); there was no effect on MetMb formation (p > 0.05). MetMb formation was inversely proportional to mitochondrial density at pH 5.6 in closed systems. Mitochondrial respiration in open systems resulted in greater MetMb and DeoMb formation at pH 5.6 and pH 7.2, respectively, vs controls (p < 0.05). The greatest MetMb formation was observed with a mitochondrial density of 0.5 mg/mL at both pH values in open systems. Mitochondrial respiration facilitated a shift in Mb form from OxyMb to DeoMb or MetMb, and this was dependent on pH, oxygen availability, and mitochondrial density.
"However, a certain amount of metmyoglobin (MMb) will always be present, in both low and high oxygen packaging, due to oxidation. It is the oxidation of KCS such as succinate and glutamate , that produces reducing equivalents that are transported from the mitochondrial membrane to reduce MMb (Phung et al., 2012, 2013; Tang et al., 2005). However, the mitochondrial membrane is a major source of reactive oxygen species (ROS) and this is especially true in meat due to the deterioration of the electron transport chain (ETC) (Barksdale, Perez-Costas, Melendez-Ferro, Roberts, & Bijur, 2010; Lenaz, 2001; Werner, Natter, & Wicke, 2010). "
"Furthermore, mitochondria isolated from dark-cutting beef are reasonably well-coupled at 5 d postmortem and perform better than mitochondria obtained from control animals at 24 h postmortem (Ashmore, Parker, & Doerr, 1972). Moreover, there are clear improvements in functional parameters of mitochondria when the pH of isolation and assay medium is increased to physiological pH (Ashmore et al., 1972; Tang et al., 2005). Thus, the main factor affecting function of mitochondria isolated in the postmortem period is development of low muscle pH. "
[Show abstract][Hide abstract] ABSTRACT: Meat quality development, or the transformation of muscle to meat, involves a myriad of biochemical pathways that are largely well-studied in living muscle tissue. However, these pathways are less predictable when homeostatic ranges are violated. In addition, there is far less known about how various management or environmental stimuli impact these pathways, either by substrate load or altered cellular environment. Likewise, it is largely accepted that oxygen plays little to no role in the conversion of muscle to meat, as anaerobic metabolism predominates in the muscle tissue. Even so, the oxygen tension within the tissues does not fall precipitously at exsanguination. Therefore, transition to an anaerobic environment may impact energy metabolism postmortem. Antemortem handling, on the other hand, clearly impacts meat quality development, yet the exact mechanisms remain a mystery. In this paper, we will attempt to review those factors known to affect postmortem energy metabolism in muscle and explore those areas where additional work may be fruitful.
"Myoglobin, present in the heart, acts as an oxygen store and can delay post-mortem-induced detrimental effects by maintaining mitochondrial activity . Morphological integrity of mitochondria is maintained in bovine cardiac muscle at 2 h post-mortem . In addition, anecdotal evidence (using metabolic radiolabelling) suggests that the human heart left ventricle tissue has the ability to synthesise new proteins up to 48 h following organ removal (Westbrook J. A., unpublished data). "
[Show abstract][Hide abstract] ABSTRACT: Protein degradation that occurs in tissue during post-mortem interval or sample preparation is problematic in quantitative analyses as confounding variables may arise. Ideally, such artefacts should be prevented by preserving the native proteome during sample preparation. We assessed the efficacy of thermal treatment (TT) to preserve the intact proteome of mouse heart and brain tissue in comparison to standard snap-freezing with liquid nitrogen (LN). Tissue samples were collected, either snap frozen (LN), subjected to TT, or snap frozen followed by thermal treatment, and subsequently analysed by 2-DE. In heart tissue, following quantitative image analysis, we observed 77 proteins that were significantly altered across the three treatment groups (ANOVA, p<0.05). Principal component and clustering analyses revealed LN and TT to be equally beneficial. These findings were confirmed by MS identification of the significantly altered proteins. In brain tissue, 189 proteins were significantly differentially expressed across the three treatment groups (ANOVA, p<0.05). Brain tissue appeared to be more responsive to TT than heart and distinct clusters of differentially expressed proteins were observed across treatments. Overall, TT of brain tissue appears to have beneficial effects on protein stabilisation during sample preparation with preservation of high-molecular-weight proteins and reduction in protein fragmentation.
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