The complete amino acid sequence was determined for the ~1-and /?-chains of the B875 light-harvesting protein purified from photosynthetic membranes of Rhodopseudomonas sphaeroides 2.4.1. The sequence of the B875-a-polypeptide was identical to that reported for the R26.1 carotenoidless mutant [( 1985) B&him. Biophys. Acta 806, 185-1861 and contained 58 amino acid residues with a blocked methionine and a glutamic acid at the N-and C-termini, respectively. The B875$-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 /%polypeptide chain and is thought to result in a weakening of the structure of the a//? heterodimer since it was not possible to isolate the intact pigmentprotein complex from the R26.1 mutant strain.
Amino acid sequence Light-harvesting protein Photosynthetic membrane
Rhodopseudomonas sphaeroidesPolyacrylamide gel electrophoresis
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