An immunological and electrophoretic study of Rhodospirillum rubrum chromatophore fragments

Abstract

Rhodospirillum rubrum chromatophores were solubilized by various detergent treatments and fractionated. The main fractions were a particle enriched in P 870 photochemical activity, a purified photochemical reaction center, and AUT “photoreceptor” particles. These fractions and others were compared to the chromatophore preparation by immunodiffusion in the presence of deoxycholate, in order to solubilize the antigenic components of the membrane. They were compared also by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and urea. These techniques show that each particle has different components. The purified reaction center preparation contains two antigens and three electrophoretic components with apparent molecular weights of 28,000, 25,500, and 21,000. These three components are present in all the fractions studied, although in small amounts in the pellet obtained after solubilization with dodecyl dimethylamine N-oxide. This fraction contains, as a major component, a polypeptide of about 10,000 apparent molecular weight which is thought to be associated with light-harvesting pigments. This polypeptide is virtually absent from purified photochemical reaction center. The reaction center protein is estimated to represent 15% of the chromatophore preparation on a protein basis.