The light-harvesting core-complex and the B820-subunit from Rhodopseudomonas marina. Part I. Purification and characterisation.

The BChla-containing B880-complex (core-complex) of Rhodopseudomonas marina (Rhodospirillaceae) was isolated with a new purification method. The isolation of the B880-complex was performed by solubilisation of the photosynthetic membranes with the detergent LDAO and subsequent fractionated ammonium-sulfate precipitation with about 50% recovery. The B880-complex retained its original spectral properties as revealed with absorption, fluorescence and circular dichroism spectroscopy. Furthermore, we dissociated the B880-complex with the detergent n-octyl-beta-glucoside (OG) and purified the developed subcomplex by the method of Miller et al. [1], which showed an absorption maximum at 820 nm (B820). The alpha- to beta-polypeptide ratio and the alpha- or beta-polypeptide to BChla ratio, respectively, were estimated to be 1:1 in both complexes. The molecular weights of the B880 and the B820-complexes, determined by gel filtration chromatography, were 181 and 32 kDa, respectively. Thus, it appears that the B880-complex of Rp. marina consists of 24 polypeptides and the B820-complex of four polypeptides. Six B820-complexes or possible subunits could form the B880-complex. On the basis of these data we propose a model for the structure of BChla containing core-complexes.