Isolation and complete amino acid sequence of the beta- and alpha-polypeptides from the peripheral light-harvesting pigment-protein complex II of Rhodobacter sulfidophilus.

The peripheral light-harvesting bacteriochlorophyll-carotenoid-protein complex B800-850 (LHII) has been isolated from membranes of semi-aerobic dark-grown cells of Rhodobacter sulfidophilus strain W4. A reversed-phase HPLC system resolved one beta- and one alpha-polypeptide in the ratio 1:1. The material obtained was of high purity and suitable for direct microsequence analysis. The primary structures of the beta- and alpha-polypeptides have been determined. The beta-polypeptide consists of 51 amino acid residues, yielding a molecular mass of 5512 Da and having 64.7% hydrophobicity. The alpha-polypeptide consists of 52 amino acid residues, with a calculated molecular mass of 5661 Da and 75% hydrophobicity. The significance of uncommon structure motives with respect to the unusual spectroscopic characteristics of this light-harvesting complex is discussed.