Cytochrome c2 of Rhodospirillum rubrum

Peptides obtained by partial digestion of cytochrome c2 of Rhodospirillum rubrum with chymotrypsin and pepsin, as well as by BrCN fragmentation and dilute acid cleavage, have been purified and their sequences have been determined. This additional information, together with earlier results obtained by digestion with trypsin and thermolysin, has permitted positive assignment of all 112 amino acid residues to unique positions in the molecule. Substantial homology between the sequence proposed for cytochrome c2 and the primary structures of mammalian cytochromes c is apparent. The relationship of all of these heme-proteins to cytochrome c of Pseudomonas fluorescens is considered. Internal homology in cytochrome c2 of R. rubrum is demonstrated for about 83% of the molecule, suggesting evolution of this protein from a small, repeating peptide unit.