The amino acid sequences of the cytochromes c-555 from two green sulphur bacteria of the genus Chlorobium.

Amino acid seauences are proposed for the cytochromes c-555 from Chlorobium thiosulphatophilum and from the Chlorobium limicola component of "Chloropseudomonas ethylica 2K". Each is a sincle polypeptide chain, the former of 86, the latter of 99 residues, and, when aligned so as to give the best match, 47 residues are common to the two sequences. The sequences show some resemblance to those of cytochromes c5 and f. The bacteriochlorophyll a-proteins were also isolated and purified, and their amino acid compositions compared (see the Appendix). There are significant differences in the compositions, but not as great as those found for the cytochromes c-555. The significance of these observations for the taxonomy of the Chlorobiaceae and for the further development of the comparative biochemistry of cytochrome c is discussed. Detailed evidence for the sequences of the cytochromes c-555 has been deposited as Supplementary Publication SUP 50073 (36 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem. J. (1976) 153, 5.