Protein components of bacterial photosynthetic membranes

Abstract

The pigmented membranes of photosynthetic bacteria, and fractions derived from them, have been analyzed by electrophoresis in polyacrylamide gels, following their dissolution by exposure to sodium dodecyl sulfate and mercaptoethanol. Purified photosynthetic reaction centers from Rhodopseudomonas spheroides yielded three components of apparent molecular weights 27, 22, and 19 kilodaltons, confirming the findings of Feher and collaborators. The density of staining suggested that RC's † † Abbreviations used: RC, photosynthetic reaction center; BChl, bacteriochlorophyll; SDS, sodium dodecyl sulfate; LDAO, lauryl dimethyl amine oxide. contain these components in a molar ratio of 1:1:1. The RC protein comprised about 25% of the total chromatophore protein. Two major chromatophore proteins, distinct from RC protein, had apparent molecular weights of 46 and 11 kdaltons. The RC proteins could not be found in any preparation made from the pigmented but non-photosynthetic mutant strain PM8 of Rhodopseudomonas spheroides. Triads of bands suggesting the three RC proteins could be discerned in preparations from Rhodospirillum rubrum, Rps. capsulata, and Rps. palustris, but not Rps. gelatinosa or Rps. viridis. Antibody specific toward RC's from Rps. spheroides did not react with any component from non-photosynthetic mutant Rps. spheroides, nor from any of the other species of photosynthetic bacteria mentioned here. The Coomassie Brilliant Blue stain was observed to be fluorescent on some bands in the gels and not on others. With the RC triad the band of highest molecular weight was fluorescent and the others were not; this set of bands was accordingly very easy to recognize in crude preparations.