Complete amino acid sequence of the B875 light-harvesting protein of Rhodopseudomonas sphaeroides strain 2.4.1. Comparison with R26.1 carotenoidless-mutant strain.

The complete amino acid sequence was determined for the alpha- and beta-chains of the B875 light-harvesting protein purified from photosynthetic membranes of Rhodopseudomonas sphaeroides 2.4.1. The sequence of the B875-alpha-polypeptide was identical to that reported for the R26.1 carotenoidless mutant [(1985) Biochim. Biophys. Acta 806, 185-186] and contained 58 amino acid residues with a blocked methionine and a glutamic acid at the N- and C-termini, respectively. The B875-beta-polypeptide contained 48 amino acid residues with alanine and phenylalanine as respective N- and C-termini; although otherwise identical, the leucine at position 29 in the wild-type strain was replaced by proline in the mutant. This radical amino acid substitution occurred within the central hydrophobic domain of the beta-polypeptide chain and is thought to result in a weakening of the structure of the alpha/beta heterodimer since it was not possible to isolate the intact pigment-protein complex from the R26.1 mutant strain.