New and unexpected routes for ultrafast electron transfer in photosynthetic reaction centers

In photosynthetic reaction centers, the excitation with light leads to the formation of a charge separated state across the photosynthetic membrane. F or the reaction center of purple nonsulphur bacteria, it was previously gen erally assumed that this primary charge separation could only start with th e excitation of the so-called special pair of bacteriochlorophyll molecules located in the heart of the RC. However, recently new and ultrafast pathwa ys of charge separation have been discovered in the bacterial RC that are d riven directly by the excited state of the accessory monomeric bacteriochlo rophyll present in the active branch of cofactors, These results demonstrat e that the route for energy conversion in photosynthesis can be much more f lexible than previously thought. We suggest that the existence of multiple charge separation routes is particularly relevant for the mechanism of char ge separation in the photosystem II reaction center of higher plants. (C) 1 999 Federation of European Biochemical Societies.