Oxygen-evolving complex

The oxygen-evolving complex (OEC), also known as the water-splitting complex, is a water-oxidizing enzyme involved in the photo-oxidation of water during the light reactions of photosynthesis. OEC is surrounded by 4 core proteins of photosystem II at the membrane-lumen interface. The mechanism for splitting water involves absorption of three photons before the fourth provides sufficient energy for water oxidation. Based on a widely accepted theory from 1970 by Kok, the complex can exist in 5 states: S0 to S4. S4 being the most oxidized and S0 the most reduced. Photons trapped by photosystem II move the system from state S0 to S4. S4 is unstable and reacts with water producing free oxygen. For the complex to reset to the lowest state, S0, it uses 2 water molecules to pull out 4 electrons. The OEC active site contains a cluster of manganese and calcium, with the formula Mn4Ca1OxCl1–2(HCO3)y. This cluster is coordinated by D1 and CP43 subunits and stabilized by peripheral membrane proteins. Other characteristics of it have been reviewed. Currently, the mechanism of the complex is not completely understood. Along with the role of Ca+2, Cl−1, and the membrane proteins surrounding the metal cluster not being well understood. Much of what is known has been collected from flash photolysis experiments, electron paramagnetic resonance (EPR), and X-ray spectroscopy.

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Related concepts (8)

Light-dependent reactions

Light-dependent reactions is jargon for certain photochemical reactions that are involved in photosynthesis, the main process by which plants acquire energy. There are two light dependent reactions, the first occurs at photosystem II (PSII) and the second occurs at photosystem I (PSI), PSII absorbs a photon to produce a so-called high energy electron which transfers via an electron transport chain to cytochrome b_6f and then to PSI. The then-reduced PSI, absorbs another photon producing a more highly reducing electron, which converts NADP^+ to NADPH.

Oxygen evolution

Oxygen evolution is the process of generating molecular oxygen (O2) by a chemical reaction, usually from water. Oxygen evolution from water is effected by oxygenic photosynthesis, electrolysis of water, and thermal decomposition of various oxides. The biological process supports aerobic life. When relatively pure oxygen is required industrially, it is isolated by distilling liquefied air. Oxygen evolving complex Photosynthetic oxygen evolution is the fundamental process by which oxygen is generated in the earth's biosphere.