Isolation and characterization of the membranes from Rhodospirillum rubrum

1. 1. The specific bacteriochlorophyll a content of Rhodospirillum rubrum was inversely related to the specific growth rate of these cells. However, the lipid-phosphorus content of isolated and purified chromatophores was directly related to the specific growth rates of the cells from which they were isolated. The specific bacteriochlorophyll a content of these chromatophores was found to be constant and independent of the specific growth rate. This constancy in the specific bacteriochlorophyll a content was not observed in chromatophores isolated from cells in the stationary phase where increases in the specific bacteriochlorophyll a content of 100% were demonstrated. 2. 2. Isolated chromatophores responded as osmometers to density gradient solutes of different osmotic properties. The density of chromatophores in Ficoll gradients increased when the non-permeable solute sucrose was added to the gradient, thus indicating that isolated chromatophores are vesicular structures which can be plasmolyzed in hypertonic solutions. 3. 3. Soluble protein was released from purified chromatophores by subjecting them to osmotic shock and sonication. No bacteriochlorophyll a, and only 30% of the total membrane protein was released during 40 min of sonication. Comparison of the number of proteins released (acrylamide gels) and the release of succinate dehydrogenase by sonication and osmotic shock suggests that succinate dehydrogenase is tightly bound to the membrane whereas there is a group of unidentified proteins which are loosely bound or trapped inside the vesicular membrane. 4. 4. In the absence of magnesium a heavy band was isolated which had a low bacteriochlorophyll a, phospholipid and succinate dehydrogenase content and high hexosamine content. Chromatophore-like material was isolated from this fraction by French pressure cell disruption followed by sucrose density centrifugation. Electron micrographs, and the ratio of bacteriochlorophyll a to phospholipid of the resulting fractions indicate that photosynthetically grown R. rubrum contains a bacteriochlorophyll a-deficient cytoplasmic membrane.