A Cytochrome b/c1 Complex with Ubiquinol–Cytochrome c2 Oxidoreductase Activity from Rhodopseudomonas sphaeroides GA

A cytochrome b/c1 complex which catalyses the reduction of cytochrome c by ubiquinol has been isolated from Rhodopseudomonas sphaeroides GA. It contains two hemes b and substoichiometric amounts of ubiquinone‐10 and of the Rieske Fe‐S center per cytochrome c1, and is essentially free of reaction center and bacteriochlorophyll. The complex consists of three major polypeptides with apparent molecular masses of 40, 34 and 25 kDa. The 34‐kDa polypeptide carries heme. Cytochrome c1 has a midpoint potential of 285 mV. For cytochrome b two midpoint potentials, at 50 and –60 mV, at pH 7.4, can be derived if one assumes two components of equal amount. Ubiquinol–cytochrome c oxidoreductase activity is specific for ubiquinol and bacterial cytochromes c, and is inhibited by antimycin A and 5‐n‐undecyl‐6‐hydroxy‐4,7‐dioxobenzothiazole. The complex shows oxidant‐induced reduction of cytochrome b.