The complete amino acid sequences of the B800-850 antenna polypeptides from Rhodopseudomonas acidophila strain 7750.
Spectrally pure B800-850 light harvesting complexes of Rhodopseudomonas acidophila 7750 were prepared by chromatography of LDAO-solubilised photosynthetic membranes on Whatmann DE-52 ion exchange resin. Two low molecular mass polypeptides (alpha, beta) have been isolated by organic solvent extraction of the lyophilised B800-850 light harvesting complexes. Their primary structures were determined by liquid phase sequencer runs, by the sequence analyses of C-terminal o-iodosobenzoic acid fragments, by hydrazinolysis and by carboxypeptidase degradation. B800-850 alpha consists of 53 amino acids and is 45.3% and 50.9% homologous to the B800-850-alpha antenna polypeptides of Rhodobacter sphaeroides and Rhodobacter capsulatus, respectively. The second very short polypeptide (B800-850-beta, 41 amino acids) is 61.0% and 56.1% homologous to the corresponding polypeptides of Rb. sphaeroides and Rb. capsulatus. The molar ratio of the two polypeptides is about 1:1. Both polypeptides show a hydrophilic N-terminal domain, a very hydrophobic central domain and a short C-terminal domain. In both polypeptides the typical His residues, identified in all antenna polypeptides of purple nonsulphur bacteria as possible bacteriochlorophyll binding sites, were found.