Effects of exogenous cytochrome c on respiratory capacity of heart and skeletal muscle

Cytochrome c is easily extracted from mitochondria by salt buffers. Yet studies of mitochondrial respiratory capacity, which routinely use KCl solutions for preparation of muscle, have failed to include the enzyme in the assay medium. The present study demonstrated that exogenous cytochrome c stimulated the oxidation of pyruvate + malate by 120, 66, 65, and 35% for the mitochondrial fraction of heart, fast-twitch red, mixed and fast-twitch white rodent muscle. Lesser increases were obtained for whole homogenate preparations. These data suggest that previous studies may have underestimated the true respiratory capacity of these tissues.