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Mitochondrial reduction of metmyoglobin: dependence on the electron transport chain.

Reduction of ferric myoglobin (metmyoglobin, MetMb) to its ferrous form is important for maintaining fresh meat color because only reduced myoglobin can bind oxygen to form the consumer-preferred cherry red color in fresh meat. The objective of this study was to characterize an apparent mitochondria electron transport chain (ETC)-linked pathway for MetMb reduction in vitro. MetMb was reduced in the presence of mitochondria and succinate (p < 0.05); mitochondria or succinate alone did not facilitate MetMb reduction relative to controls (p > 0.05). Flushing samples with oxygen greatly decreased MetMb reduction, while flushing with argon increased MetMb reduction when compared with controls (p < 0.05). ETC inhibitors were used to localize the site where electrons became available for MetMb reduction. MetMb reduction was increased by rotenone addition and decreased by malonic acid (p < 0.05); the reduction was completely abolished by additions of antimycin A or myxothiazol when compared with controls (p < 0.05). These results suggest that electrons become available for MetMb reduction at a site(s) between complex III and IV. Mitochondrial ETC-linked MetMb reduction increased with increased mitochondrial density and succinate concentration (p < 0.05); the greatest MetMb reduction was observed at pH 7.2 and 37 degrees C, and ETC-linked MetMb reducing activity decreased with time postmortem (p < 0.05). These results indicate that ETC-linked MetMb reduction exists but would be minimally active in postmortem muscles.