Photosynthesis Oxygen-evolving complex

The invention of aerobic photosynthesis, the light-driven oxidation of water to oxygen, stands as one of the pivotal evolutionary innovations in the history of life on Earth. The process is carried out only at the oxygen-evolving complex (OEC) of PSII in plants and algae, as well as in cyanobacteria. Despite the biological uniqueness of water oxidation to 02, several of the core proteins of PSII have homologues in the so-called type I and type II anaerobic photosynthetic reaction... 

Fig. 4.7. The Z scheme of the higher plant photosynthetic chain visualized as an arrangement of multiprotein complexes. The two RC of PSII and PSI are arranged in parallel across the membrane and are intereonnected by the b /f complex. The electron transfer pathway within this complex follows a modified Q cycle scheme analogous to that proposed for bacterial photosynthesis. The oxygen-evolving complex is proposed to face the inner thylakoid lumen and to release protons in this compartment. The association of cytochrome 6-559 with PSII-RC and the cyclic role of ferredoxin are also depicted. Proton-binding and proton-releasing sites are illustrated (from Ref. 93).

Oxygen produced in photosynthesis comes from water. The oxygen-evolving complex is part of the series of electron-transfer reactions from water to NADPH. Carbon dioxide is involved in the dark reactions, which are different reactions that take place in another part of the chloroplast... 

Bricker TM, Ghanotakis DF. Introduction to oxygen evolution and the oxygen-evolving complex. In Ort DR, Yocum CF, eds. Advances in Photosynthesis The Light Reactions. Vol. 4. Dordrecht Kluwet Academic Publishers, 1996 113-136. 

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