Photosynthetic Oxidation of Water — Oxygen Evolution

Introduction Mn Chemistry and Biochemistry Photosynthetic Oxidation of Water — Oxygen Evolution Mn and Detoxification of Oxygen Free Radicals Nonredox di-Mn Enzymes — Arginase 

The other property of Mn which has important biochemical consequences is that it is a close, but not exact, surrogate of Mg. As we saw in Chapter 10, Mg is confined to a strict octahedral coordination geometry, with ligand bond angles close to 90°, making it an ideal stmcturaF cation, particularly for phosphorylated biological 

The major role of manganese in biology is in oxygen production by photosynthetic plants, algae, and cyanobacteria. It is also involved in a number of mammalian enzymes like arginase and mitochondrial superoxide dismutase and it also plays an important role in microbial metabolism. Most of manganese biochemistry can be 

Somewhere around 2.5Ga ago, an enzyme activity emerged which dramatically changed the chemical composition of the earth s atmosphere forever, resulting in a veritable explosion of biological activity. The enzyme. 

This provided an unlimited supply of reducing equivalents to convert CO2 to carbohydrates, and subsequently to the other organic molecules of life  

The water-plastoquinone photo-oxidoreductase, also known as photosystem II (PSII), embedded in the thylakoid membrane of plants, algae and cyanobacteria, uses solar energy to power the oxidation of water to dioxygen by a special centre containing four Mn ions. The overall reaction catalysed by PSII is outlined below  

Clearly, the S0 state must have one Mn(II), one Mn(III) and two Mn(IV) while the S4 must have three Mn(IV) and one Mn(V)—but where they are located in the tetra-Mn centre and how their four-electron reduction is coupled with water splitting and dioxygen evolution remains to be established. (For recent reviews see Goussias et al., 2002 Ferreira et al., 2004 Rutherford and Boussac, 2004 Iverson, 2006.) 

(2004) Arginine metabolism enzymology, nutrition and clinical significance, J. Nutr., 134, 

Barynin, V.V., Whittaker, M.M., Antonyuk, S.V., Lamzin, V.S., Harrison, P.M., Artymiuk, PJ. and Whittaker, J.W. (2001) Crystal structure of manganese catalase from Lactobacillus plantarum, 

Ferreira, K.N., Iverson, T.M., Maghlaoui, K., Barber, J. and Iwata, S. (2004) Architecture of the photosynthetic oxygen-evolving center, Science, 303, 1831-1838. 

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