Oxygen evolving complex
Encyclopedia
The oxygen-evolving complex, (OEC) also known as the water-splitting complex, is a water-oxidizing enzyme involved in the photooxidation of water
during the light reactions of photosynthesis. Based on a widely accepted theory from 1970 by Kok, the complex can exist in 5 states: S0 to S4. Photons trapped by photosystem II
move the system from state S0 to S4. S4 is unstable and reacts with water to produce free oxygen
. Currently, the functional mechanism of the complex is not completely understood. Much of the known data have been collected from flash experiments, EPR, and X-ray spectroscopy.
The OEC appears to have a metalloenzyme core containing both manganese
and calcium
, with the empirical formula for the inorganic core of Mn4Ca1OxCl1–2(HCO3)y. Other characteristics of it have been reviewed; see
It is suggested that the evolution of OEC is triggered by the presence of the manganese
-containing minerals rancieite and hollandite in the early oceans. The minerals were, it is presumed, assimilated by the early Cyanobacteria, which have incorporated them in the active center of the complex.
Oxygen evolution
Oxygen evolution is the process of generating molecular oxygen through chemical reaction. Mechanisms of oxygen evolution include the oxidation of water during oxygenic photosynthesis, electrolysis of water into oxygen and hydrogen, and electrocatalytic oxygen evolution from oxides and...
during the light reactions of photosynthesis. Based on a widely accepted theory from 1970 by Kok, the complex can exist in 5 states: S0 to S4. Photons trapped by photosystem II
Photosystem II
Photosystem II is the first protein complex in the Light-dependent reactions. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. The enzyme uses photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce...
move the system from state S0 to S4. S4 is unstable and reacts with water to produce free oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. Currently, the functional mechanism of the complex is not completely understood. Much of the known data have been collected from flash experiments, EPR, and X-ray spectroscopy.
The OEC appears to have a metalloenzyme core containing both manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
and calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
, with the empirical formula for the inorganic core of Mn4Ca1OxCl1–2(HCO3)y. Other characteristics of it have been reviewed; see
It is suggested that the evolution of OEC is triggered by the presence of the manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
-containing minerals rancieite and hollandite in the early oceans. The minerals were, it is presumed, assimilated by the early Cyanobacteria, which have incorporated them in the active center of the complex.