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 density measurement of the antenna solutions provided the values of the buoyant factor of both complexes. Phospholipid content was measured in both antennae. Sedimentation velocity and equilibrium centrifugation indicated that the B800-850 sample is monodisperse and composed from heptamers (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 hydroxyspheroidene)(12); larger oligomers probably coexist. The amount of bound detergent could be calculated. B800-850 binds about 0.4-0.5 g of lauryl-dimethyl-amine oxide per g of protein (i.e., 28-35 detergent molecules per alpha/beta), while a large amount of detergent (2.3 g of decanoylsucrose per g of protein, i.e., 64 detergent molecules per alpha/beta) is bound to B875. The electron microscopy images of both antennae in detergent solutions after negative staining are presented and compared to the centrifugation results.