Formation of a subunit form of the core light-harvesting complex from sulfur purple bacteria Ectothiorhodospira haloalkaliphila with different carotenoid composition

Abstract

B820 subunits from a purple sulfur bacterium Ectothiorhodospira haloalkaliphila strain ATCC 51935^T were obtained by treatment of carotenoid free LH1-RC complexes of this bacterium with ß-octylglucopyranoside (ß-OG). The same complexes with 100% carotenoid content were unable to dißsociate to B820 subunits, but disintegrated to monomeric bacteriochlorophyll (BChl) regardless of their carotenoid composition. The degree of dissociation of the LH1-RC complexes with an intermediate content of carotenoids (the B820 formation) was directly dependent on the quantity of carotenoids in the samples. The resulting B820 subunits did not contain carotenoids. B820 subunits easily aggregated to form a complex with an absorption peak at 880 nm at decreased ß-OG concentration. Analysis of the spectra of the LH1-RC complexes isolated from the cells with different levels of carotenogenesis inhibition led to the conclusion of the heterogeneity of the samples with a predominance of them in (a) the fraction with 100% of carotenoids and (b) the fraction of carotenoid-free complexes.