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. For the reaction center of purple nonsulphur bacteria, it was previously generally assumed that this primary charge separation could only start with the excitation of the so-called special pair of bacteriochlorophyll molecules located in the heart of the RC. However, recently new and ultrafast pathways of charge separation have been discovered in the bacterial RC that are driven directly by the excited state of the accessory monomeric bacteriochlorophyll present in the active branch of cofactors, These results demonstrate that the route for energy conversion in photosynthesis can be much more flexible than previously thought. We suggest that the existence of multiple charge separation routes is particularly relevant for the mechanism of charge separation in the photosystem II reaction center of higher plants. (C) 1999 Federation of European Biochemical Societies.