Purification and primary structure analysis of two cytochrome c_2 isozymes from the purple phototrophic bacterium Rhodospirillum centenum

摘要

The isolation and amino acid sequences of two cytochromes c-552 from the thermotolerant bacterium Rhodospirillum (R.) centenum have been determined. They are very similar to one another with 85% identity. They are homologous to the cytochromes c_2 from purple bacteria with approximately 67% identity to that from Rhodopseudomonas (Rps.) palustris compared to only 42% identity with others of the c_2 subclass. In addition, they share an unusual six-residue insertion with Rps. palustris cytochrome c_2 not found in any other cytochrome. The relationship with Rps. palustris is thus highly significant. The redox potentials of the R. centenum isozymes are 293 and 316 mV. Although the proteins have strongly different iso-electric points, both have three conserved lysine residues at the proposed site of electron transfer. These results suggest that they may be functionally interchangeable.