Postmortem oxygen consumption by mitochondria and its effects on myoglobin form and stability

Department of Animal Science, University of Connecticut, 3636 Horsebarn Hill Road Ext., Storrs, Connecticut 06269-4040, USA.
Journal of Agricultural and Food Chemistry (Impact Factor: 3.11). 02/2005; 53(4):1223-30. DOI: 10.1021/jf048646o
Source: PubMed

ABSTRACT 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.

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    • "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. "
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