Protein composition of intact and fractionated memberanes isolated from dark and light grown cells of a blue green mutant of Rhodospirillum Rubrum (BG1)

Abstract 1. By means of different fractionation procedures we have separated two major protein fractions present in photosynthetically grown cells of the blue-green mutant of Rhodospirillum rubrum (BG 1 ). These proteins are found in differing amounts in the two subchromatophore fragments produced by the detergent Triton X-100. A more extensive breakdown caused by digestion of intact photosynthetic membrane with Triton X-100 and trypsin produced four main protein fractions which were separated by means of gel electrophoresis. Some of these bands originated from proteins that were intimately associated with bacteriochlorophyll in the intact membrane. The other protein fractions seem to derive from a group of proteins whose function could be a supporting one. These protein fractions seem to be a somewhat degraded form of the basic membrane core that cannot be further attacked by the combined action of the detergent and the trypsin. 2. Electron micrographs of the fractions obtained by the digestion with Triton X-100 and trypsin are presented, showing a very different structure for the degraded basic membrane and a unique structure for the aggregated units of the bacteriochlorophyll-containing fraction.