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

Abstract

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‐β‐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 α‐ to β‐polypeptide ratio and the α‐ or β‐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 or BChla containing core‐complexes.