PRIMARY PROCESSES IN PHOTOSYNTHETIC REACTION CENTERS

Photosynthetic reaction centers realize the primary steps of the bioconversion of light energy. They are complex membrane proteins which contain several molecules of pigments and electron carriers, organized so as to transfer electrons efficiently along a well-defined path. Reactions centers can be classified in four categories found in purple bacteria (the best known), in green sulfur bacteria, and in plants (which have two categories : PS-I and PS-II). Reaction centers share common properties, which are discussed mainly on the basis of what is known in purple bacteria. The following aspects are considered : coupling between reaction centers and antenna ; the role of the membrane ; the means to minimize wasteful charge recombination ; the primary step and the dimeric structure of the primary electron donor ; the properties of quinones ; the role of a Fe2+ atom; the roles of the protein ; the symmetric structure of the reaction center ; the primary radical pair and triplet state formation. © 1990 IUPAC