Nov 25, 2005

The mechanism of photosynthetic water splitting

Photochemical & Photobiological Sciences : Official Journal of the European Photochemistry Association and the European Society for Photobiology
James P McEvoyG W Brudvig

Abstract

Oxygenic photosynthesis, which provides the biosphere with most of its chemical energy, uses water as its source of electrons. Water is photochemically oxidized by the protein complex photosystem II (PSII), which is found, along with other proteins of the photosynthetic light reactions, in the thylakoid membranes of cyanobacteria and of green plant chloroplasts. Water splitting is catalyzed by the oxygen-evolving complex (OEC) of PSII, producing dioxygen gas, protons and electrons. O(2) is released into the atmosphere, sustaining all aerobic life on earth; product protons are released into the thylakoid lumen, augmenting a proton concentration gradient across the membrane; and photo-energized electrons pass to the rest of the electron-transfer pathway. The OEC contains four manganese ions, one calcium ion and (almost certainly) a chloride ion, but its precise structure and catalytic mechanism remain unclear. In this paper, we develop a chemically complete structure of the OEC and its environment by using molecular mechanics calculations to extend and slightly adjust the recently-obtained X-ray crystallographic model with reference to this structure and to some important recent experimental results.

Mentioned in this Paper

In Silico
Biochemical Pathway
Manganese
Dioxygen
Thylakoid Membrane
Plain X-ray
Calcium ion
Chloroplasts
Protein Complex Location
Thylakoid Lumen

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