Isolation and characterization of a structural subunit from the core light-harvesting complex of Rhodobacter sphaeroides 2.4.1 and puc705-BA.

A method for isolating a structural subunit, B825, from the B875 core light-harvesting complex (LHC) of Rhodobacter sphaeroides 2.4.1 (wild-type) and a B800-B850(-) mutant, puc705-BA, is presented. This method, based on one developed to prepare a similar subunit, B820, from the core LHC of Rhodospirillum rubrum [Miller et al., Biochemistry 26, 5055-5062 (1987)], requires the dissociation of treated chromatophores with the detergent, octyl-glucoside. A subsequent gel filtration step separates B800-850 (if present), reaction centers, and free bacteriochlorophyll from the subunit complex. B825 was quantitatively reassociated into an 873 nm absorbing form which resembled the in vivo complex as judged by its absorption properties. The polypeptides in B825 and B800-850 were isolated by HPLC and identified by N-terminal amino acid sequencing. Two polypeptides, alpha and beta, were found in each complex in a 1:1 ratio. The spectral and biochemical properties of the subunits isolated from Rhodospirillum rubrum, Rhodobacter sphaeroides, and Rhodobacter capsulatus are compared.