The Light-Harvesting Polypeptides ofRhodopseudomonas viridis.The Complete Amino-Acid Sequences of B1015-α, B1015-β and B1015-γ

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Abstract
Three low MW polypeptides were isolated using organic solvent extraction of thylakoid membranes or whole cells from R. viridis. Their primary structures were determined by long liquid phase sequencer runs, combined with the isolation and sequence analysis of the C-terminal o-iodosobenozic acid fragment and carboxypeptidase degradation. The polypeptide which consists of 58 amino acid and is 46% homologous to the antenna polypeptide B880-.alpha.-from Rhodospirillum rubrum was designated as B1015-.alpha. (1 His residue). The sequence homology between the 2nd polypeptide, named B1015-.beta. (55 amino acids, 2 His residues) and B880-.beta. from R. rubrum is 52%. For the 3rd polypeptide consisting of 36 amino acids and exhibiting a high hydrophobicity, no equivalent polypeptide was so far found in other purple bacteria. The molar ratio of these three organic solvent soluble polypeptides from R. viridis was estimated to be 1:1:1. The 36 amino acid polypeptide is likely to be an additional constituent of the light-harvesting complex B1015, consequently termed as B1015-.gamma.. According to hydropathy profiles, the transmembrane arrangement of B1015-.alpha. and B1015-.beta. within the thylakoid membrane is supposed to be similar. B1015-.gamma., however, shows a somewhat different hydropathy profile. A particular feature of this polypeptide is its high amount of aromatic amino acids. It is postulated that B1015-.gamma. is involved in the formation of regular arrays of light-harvesting complexes.

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