Amino acid identities in the three redox center-carrying polypeptides of cytochrome bc1/b6f complexes.

The comparison of primary structures is extended to 22 cytochromes b or b6, 12 cytochromes c1 or f, and 8 Rieske FeS proteins. Conclusions are drawn as to their phylogenetic relationship as well as on conserved, functionally important amino acids and secondary structures. The results are in favor of two independent quinone binding sites at opposite surfaces of the membrane, topping one of the two hemes of cytochrome b each.