Abstract
The light-harvesting complex B880 from R. rubrum S 1 (wild type) and B870 from the carotenoidless mutant G-9+ consisted mainly of an organic solvents (chloroform/methanol)-soluble and an organic solvent-insoluble polypeptide. The isolation and separation of these 2 low-MW polypeptides (MW 6101 and MW 6079) were achieved by a 2-step extraction procedure of chromatophores using in the 1st step chloroform/methanol containing 0.1 M ammonium acetate. Following Sephadex LH-60 chromatography of this 1st extract a light-harvesting polypeptide (B870-.alpha.) was isolated and its complete amino acid sequence was determined. Upon reextraction of the chromatophore pellet with chloroform/methanol/ammonium acetate containing in addition acetic acid, a 2nd low MW polypeptide (B880-.beta. of B870-.beta.) was generated. The complete amino acid sequences of the chloroform/methanol-insoluble light-harvesting polypeptide of R. rubrum S1 (B880-.beta.) and of R. rubrum G-9+ (B870-.beta.) were determined. They are identical and consist of 54 amino acid residues. The conserved histidine residue within the hydrophobic stretch raises more evidence for ligand complexation of bacteriochlorophyll to this specific histidine residue, which therefore possibly plays the key role in pigment-protein interactions. Both polypeptides (B880-.alpha. and B880-.beta.) are part of the light-harvesting complex B880 in an apparent ratio of 1:1. Based on the primary structure data, a possible arrangement of both light-harvesting polypeptides within the membrane is discussed.

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