Ubiquinone reduction, photosynthetic reaction center

Figure 1. The major transmembrane photosynthetic reaction centers (RC) (top) and respiratory complexes (bottom) are composed of light (zigzag) activated chains (dark gray) of redox centers (open polygons) that create a transmembrane electric field and move protons (double arrows) to create a transmembrane proton gradient, fulfilling the requirements of Mitchell s chemiosmotic hypothesis. Diffusing substrates include ubiquinone (hexagon) and other sources of oxidants and reductants. PSI and PSII, photosystems I and II, respectively.

Photosynthetic reaction centers plug into the chemiosmotic scheme by using light-excited states to create both an oxidant and a reductant. For the purple bacterial reaction centers, these oxidants and reductants are the redox carriers already described, oxidized cytochrome c and reduced ubiquinone QH2. Thus, in combination with Complex III, light drives a relatively straightforward cyclic electron transfer that generates a transmembrane electric field and proton gradient. 

Simulating Thermochemistry of p-Benzo-quinone Reduction and Binding of Ubiquinone in the Photosynthetic Reaction Center... 

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