THE ISOLATION OF THE B812 SUBCOMPLEX OF THE B880 CORE COMPLEX AND THEB800-850 COMPLEX FROM MEMBRANES OF CHROMATIUM-MINUTISSIMUM WITH EXTRACTED CAROTENOIDS - THE STRUCTURAL ROLE OF CAROTENOIDS

The isolation of the B800-850 complex and the B812 subcomplex of the B 880 core complex from membranes of Chromatium minutissimum with partia lly extracted carotenoids is presented. This method, based on that dev eloped to isolate a similar subcomplex (B820) from the B880 core compl ex of Rhodospirillum rubrum (Miller et al., Biochemistry, 26 (1987) 50 55-5062) with some modification, requires the treatment of chromatopho res with octylglucoside followed by electrophoresis in polyacrylamide gel. It separates the B880-RC assembly enriched with reaction centres (RCs) and carotenoids but depleted of a significant amount of the B880 (core) complex, the carotenoidless B812 subcomplex of the B880 core c omplex and the B800-850 complex with a reduced level of carotenoids. T he spectral and biochemical characteristics of the B812 subcomplex are the same as those of similar complexes from non-sulphur bacteria. The B800-850 complex exhibits stronger reversible conformational changes (hypsochromic shift of the band centred at 855 nm on treatment with de tergent) compared with the control. The role of carotenoids in the str ucture of these complexes is discussed.