The Amino Acid Sequence of Chlorella fusca Plastocyanin

The sequences proposed in Fig. 1 for the Ps. aerirgirioJa and Ps. strrtzeri proteins have been confirmed by the isolation and characterization of the expected peptides from tryptic digests of the haeni-free proteins. From each of these two proteins a second tryptic peptide was isolated that contained two residues of cysteine and a residue of histidine. The amino acid composition was such that the peptide could not have been derived from the region shown in Fig. 1. The N-terminal heptapeptide sequence of the cytochromes c4 is very similar to the N-terminus of Rhodospirillirm rubrum cytochrome c2 (Dus et a/., 1968). A similar Nterminal sequence, Tyr-A?p-Ala-Ala-Ala-Gly-Lys-, has also been detected in another monohaem cytochrome c from a photosynthetic bacterium, the cytochrome 12-555 of Chlorobium thiostilfatophilurn (Gibson, 1961 ; R. P. Ambler & T. Meyer, unpublished work). The very close similarity between the cytochromes c4 of A. vinelandii and the pseudonomads was unexpected. The organisms are very different in metabolism and in subcellular structure, and in the current classification (Breed et al., 1957) are placed in different orders. However, they all have G I C contents of their DNA in the range 56-66% (Hill, 1966). The deiiitrifying pseudomonads contain a wide range of haem-c-containing proteins. In addition to cytochromes c-551, c4 and c5 they contain cytochrome c peroxidase (Kodama & Mori, 1969; Ellfolk & Soininen, 1970) and cytochrome c oxidase (Horio et al., 1961). The interrelation of these components is still obscure (Horio & Kamen, 1970).