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Abstract

Located within photosynthetic membranes, reaction centers (RCs) are defined as the minimal functional units that cancatalyze light-induced electron transfer reactions, thus stabilizing the separation of charged species across the membrane. The RC essentially functions as a ferrocytochrome c₂:quinone photo-oxidoreductase. The absorption of two photons of light leads to two one-electron oxidations of cytochrome c₂ in the periplasm and to the two-electron reduction of a quinone, which is coupled to the uptake of two protons from the cytoplasm. The resulting quinol then leaves its binding site, diffuses in the photosynthetic membrane and is reoxidized by a second membrane protein complex, the cytochrome bc₁ complex, which results in proton release to the periplasm. The electrons are transferred to re-reduce the cytochrome c₂ in the periplasm. This net proton transport produces a trans-membrane electrochemical proton potential that can drive ATP synthesis through a third membrane-spanning complex, the ATP synthase.