OLIGOMERIC STATE OF THE LIGHT-HARVESTING COMPLEXES B800-850 AND B875 FROM PURPLE BACTERIUM RUBRIVIVAX-GELATINOSUS IN DETERGENT SOLUTION

Molecular weights of the purified light-harvesting complexes B800-850 and B875 from purple bacterium Rubrivivax gelatinosus were determined in detergent solutions by analytical centrifugation. The precise densi ty measurement of the antenna solutions provided the values of the buo yant factor of both complexes. Phospholipid content was measured in bo th antennae. Sedimentation velocity and equilibrium centrifugation ind icated that the B800-850 sample is monodisperse and composed from hept amers (alpha/beta/3 Bacteriochlorophyll a/1.3 Carotenoid)(7). B875 is not monodisperse but analysis of equilibrium centrifugation indicated that its smallest oligomer is a dodecamer (alpha/beta/2 BChla/2 hydrox yspheroidene)(12); larger oligomers probably coexist. The amount of bo und detergent could be calculated. B800-850 binds about 0.4-0.5 g of l auryl-dimethyl-amine oxide per g of protein (i.e., 28-35 detergent mol ecules per alpha/beta), while a large amount of detergent (2.3 g of de canoylsucrose per g of protein, i.e., 64 detergent molecules per alpha /beta) is bound to B875. The electron microscopy images of both antenn ae in detergent solutions after negative staining are presented and co mpared to the centrifugation results.