Low-temperature studies of electron transfer between different cytochromes c and cytochrome c oxidase

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Abstract
The ability of various native and modified cytochromes c to transfer electrons to cytochrome oxidase is compared in cytochrome c depleted beef heart mitochondrial particles. The kinetics are followed at -49.degree. C after the reaction is initiated by photolysis of the CO compound of cytochrome oxidase in the presence of O2. Horse, human, yeast iso-2 and carboxydinitrophenyl (CDNP)-lysine-60 horse cytochromes c all give initial rates of electron transfer that are equal to those observed in whole beef mitochondria. Euglena CDNP-lysine-72 and CDNP-lysine-13 horse cytochromes c give rates about 1/10 of that of whole mitochondria. These rates were independent of the concentration of cytochrome c. Since the inhibited cytochromes c, but not the active proteins, had previously been shown to have lowered affinity for cytochrome oxidase, the results indicate that the structural characteristics important for the association of cytochrome c and oxidase are also essential for achieving normal rates of electron transfer within the complex once formed.