MORPHOGENESIS OF PHOTOSYNTHETIC APPARATUS IN RHODOSPIRILLUM RUBRUM .I. ISOLATION ANC CHARACTERIZATION OF 2 MEMBRANE SYSTEMS

1. 1. Two pigmented bands from cell-free extracts of light-growth Rhodospirillum rubrum could be isolated in a linear gradient of Ficoll by zone centrifugation. 2. 2. As shown by several methods, the lower band of the gradient contained chromatophores (thylakoids) in a highly purified form. 3. 3. In the upper band of the gradient, particles with an average diameter of 360 Å could be identified by electron microscopy. 4. 4. Electrophoresis of the contents of the upper band in agar gel (0.5%) made it possible to separate two zones. Whereas only protein could be determined in the faster migrating zone, protein, pigments, lipids and activity of succinate dehydrogenase could be determined in the slower migrating zone. 5. 5. The chromatophores (thylakoids) of the lower band were split by treatment with phenol-formic acid-water (2:1:1, v/v/v) and then separated by gel electrophoresis in polyacrylamide into 5 main subunits. 6. 6. When the upper band of the gradient was treated with phenol-formic acid-water and separated by gel electrophoresis in polacrylamide, only one of the 5 main subunits was obtained. This was characteristic of cytoplasmic membrane. 7. 7. The upper band of the gradient could be isolated from cultures grown under anaerobic light conditions, from cultures grown aerobically in the dark and from the carotenoid-free mutant strain of R. rubrum M 46, which forms only few chromatophores. 8. 8. The results indicate that the upper band of the Ficoll gradient consists mainly of mechanically disrupted cytoplasmic membrane. 9. 9. Morphogenetic relationships between cytoplasmic membrane and chromatophores are discussed. © 1969.