Merck

Photosynthesis. Electronic structure of the oxygen-evolving complex in photosystem II prior to O-O bond formation.

Science (New York, N.Y.) (2014-08-16)
Nicholas Cox, Marius Retegan, Frank Neese, Dimitrios A Pantazis, Alain Boussac, Wolfgang Lubitz
RESUMEN

The photosynthetic protein complex photosystem II oxidizes water to molecular oxygen at an embedded tetramanganese-calcium cluster. Resolving the geometric and electronic structure of this cluster in its highest metastable catalytic state (designated S3) is a prerequisite for understanding the mechanism of O-O bond formation. Here, multifrequency, multidimensional magnetic resonance spectroscopy reveals that all four manganese ions of the catalyst are structurally and electronically similar immediately before the final oxygen evolution step; they all exhibit a 4+ formal oxidation state and octahedral local geometry. Only one structural model derived from quantum chemical modeling is consistent with all magnetic resonance data; its formation requires the binding of an additional water molecule. O-O bond formation would then proceed by the coupling of two proximal manganese-bound oxygens in the transition state of the cofactor.

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