UNEXPECTED SIMILARITIES OF THE B800-850 LIGHT-HARVESTING COMPLEX FROMRHODOSPIRILLUM-MOLISCHIANUM TO THE B870 LIGHT-HARVESTING COMPLEXES FROM OTHER PURPLE PHOTOSYNTHETIC BACTERIA

The B800-850 light-harvesting complex (also called LH2) was isolated f rom photosynthetic membranes of Rhodospirillum molischianum DSM 119 us ing molecular sieve and ion-exchange chromatography. Its two bacterioc hlorophyll a-binding polypeptides (alpha-subunit and beta-subunit) wer e purified with a reverse-phase HPLC system. The complete amino acid s equences of both subunits have been determined. The alpha- and beta-su bunits consist of 56 and 45 amino acids, respectively, corresponding t o molecular weights of 5939 and 5133. In contrast to the B800-850 comp lexes from other photosynthetic bacteria, the native B800-850 complex from Rs. molischianum is most likely an octamer of monomers with a sto ichiometry of three bacteriochlorophyll a and 1.5 lycopenes per alpha, beta-subunit. Resonance Raman spectra provide evidence for a 5-coordin ated Mg2+ in the BChl, and a carotenoid mainly in the all-trans config uration. A comparison between resonance Raman data from different phot osynthetic bacteria indicates that the BChl a-binding site of the B800 -850 complex from Rs. molischianum is more similar to the B870 complex es (also called LH1) than to the B800-850 complexes of other photosynt hetic bacteria. Sequence similarities especially between the beta-subu nits of the B800-850 complex of Rs. molischianum and the B870 and B800 -850 complexes of other photosynthetic bacteria agree with this result and provide information on the mode of pigment binding in bacterial a ntenna complexes.