PROBING THE STRUCTURE OF THE CORE LIGHT-HARVESTING COMPLEX (LH1) OF RHODOPSEUDOMONAS-VIRIDIS BY DISSOCIATION AND RECONSTITUTION METHODOLOGY

A subunit complex was formed from the core light-harvesting complex (L H1) of bacteriochlorophyll(BChl)-b-containing Rhodopseudomonas viridis . The addition of octyl glucoside to a carotenoid-depleted Rps. viridi s membrane preparation resulted in a subunit complex absorbing at 895 nm, which could be quantitatively dissociated to free BChl b and then reassociated to the subunit. When carotenoid was added back, the subun it could be reassociated to LH1 with a 25% yield. Additionally, the Rp s. viridis alpha- and beta-polypeptides were isolated, purified, and t hen reconstituted with BChl b. They formed a subunit absorbing near 89 5 nm, similar to the subunit formed by titration of the carotenoid dep leted membrane, but did not form an LH1-type complex at 1015 nm. The s ame results were obtained with the beta-polypeptide alone and BChl b. Isolated polypeptides were also tested for their interaction with BChl a. They formed subunit and LH1-type complexes similar to those formed using polypeptides isolated from BChl-a-containing bacteria but displ ayed 6-10 nm smaller red shifts in their long-wavelength absorption ma xima. Thus, the larger red shift of BChl-b-containing Rps. viridis is not attributable solely to the protein structure. The beta-polypeptide of Rps. viridis differed from the other beta-polypeptides tested in t hat it could form an LH1-type complex with BChl a in the absence of th e alpha and gamma-polypeptides. It apparently contains the necessary i nformation required to assemble into an LH1-type complex. When the gam ma-polypeptide was tested in reconstitution with BChl a and BChl b wit h the alpha- and beta-polypeptides, it had no effect; its role remains undetermined.