Molecular-organization and biosynthesis of pigment-protein complexes of Rhodopseudomonas capsulata.

The photosynthetic apparatus of the facultative phototrophic bacterium Rhodopseudomonas capsulata contains three bacteriochlorophyll-carotenoid-protein complexes: the reaction center and the light-harvesting (LH) antenna complexes LHI (B870) and LHII (B800--850). In contrast to green anoxygenic phototrophic bacteria and the oxygenic cyanobacteria, the light-harvesting complexes of Rhodospirillaceae and Chromatiaceae are integral membrane particles. Variations in light fluxes induce membrane differentiation mainly expressed as variations in the size of the photosynthetic unit and in the area of intracytoplasmic membrane per cell. The B800--850 complex is the variable part of the photosynthetic apparatus. Synthesis of bacteriochlorophyll and of the polypeptides of the pigment complexes was found to be strongly coordinated. The synthesis of these polypeptides was followed immediately by the assembly of the complexes in the membrane. Bacteriochlorophyll or a signal substance triggered by bacteriochlorophyll synthesis regulated the synthesis of these polypeptides at the level of translation. The pigment-binding subunits of the B800--850 complex form oligomeric structures which interact with subunit H of the reaction center. A model of the topographical relationships of the pigment complexes is discussed.