Supramolecular organisation of the photosynthetic chain in anoxygenic bacteria.

This minireview summarizes our present view of the supramolecular organization of the photosynthetic apparatus of Rhodobacter sphaeroides and Rhodobacter capsulatus. These two species present a close association between two reaction centers (RCs), one cytochrome (cyt) bc(1) and one cyt c. In R. sphaeroides, the RCs are only partially surrounded by LH1 complexes. This open ring of LH1 complexes is required for an efficient photoinduced cyclic electron transfer only under conditions where the quinone pool totally reduced. When the quinone pool is partially oxidized, a closed ring of LH1 complexes around the RCs does not impair the exchange of quinone molecules between the RC and the cyt bc(1) complex. To explain the efficient photochemistry of the various species which possess a RC surrounded by a closed ring of LH, it is proposed that their quinone pool is partially oxidized even under anaerobic condition.