THE LIGHT-HARVESTING COMPLEX-II (B800-850) OF RHODOBACTER-SULFIDOPHILUS - CHARACTERIZATION AND FORMATION UNDER DIFFERENT GROWTH-CONDITIONS

The photosynthetic bacterium Rhodobacter sulfidophilus is able to grow chemotrophically and phototrophically at a broad range of light inten sities. In contrast to other facultative phototrophs, R. sulfidophilus synthesizes reaction center and light-harvesting (LH) complexes, B870 (LHI) and B800-850 (LHII) even under full aerobic conditions in the d ark. The content of bacteriochlorophyll (BChl) varied from 3.8 mu g Bc hl per mg cell protein when grown at high light intensity (20 000 lux) to 60 mu g Bchl per mg cell protein when grown at low light intensiti es (6 lux). After a shift from high light to low light conditions, the size of the photosynthetic unit increased by a factor of 4. Chromatog raphic analysis of the LHII complex, isolated and purified from cells grown phototrophically (at high and low light intensities) and chemotr ophically, could resolve only one type of alpha and one type of beta p olypeptide in the purified complex, of which the N-terminal sequences have been determined.