EVIDENCE FOR BINDING-SITES ON CYTOCHROME-C FOR OXIDASES AND REDUCTASES FROM STUDIES OF DIFFERENT CYTOCHROMES C OF KNOWN STRUCTURE

Assays of cytochrome c oxidase and succinate- and NADH-cytochrome c reductase activities indicate that cytochromes c from beef, Paracoccus denitrificans, and Rhodospirillum rubrum all possess effective binding sites for reaction with eukaryotic and P. denitrificans reductase systems. P. denitrificans and beef cytochromes c have binding sites for the oxidase of both species, but R. rubrum cytochrome c2 does not. Since the tertiary structures of the 3 cytochromes are known, the data give evidence for localization of the oxidase and reductase binding sites on the surface of the molecule. These appear to be separate sites, both of which are in the area around the heme crevice. The cytochrome c from P. denitrificans can bind poly(L-lysine), presumably because of a localized area of negative charge on the surface of the molecule. This binding can stimulate the oxidation of the P. denitrificans cytochrome c by the oxidase of either beef or P. denitrificans, giving additional evidence for the involvement of charged groups in the reaction of cytochrome c with the oxidase.