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The diverse functions of calcium in natural water oxidation

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Pantazis,  Dimitrios A.
Research Department Neese, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Retegan,  Marius
Research Department Neese, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Krewald,  Vera
Research Department Neese, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Neese,  Frank
Research Department Neese, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Cox,  Nicholas
Research Department Lubitz, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Pantazis, D. A., Retegan, M., Krewald, V., Neese, F., & Cox, N. (2014). The diverse functions of calcium in natural water oxidation. Talk presented at 12th European Biological Inorganic Chemistry Conference. Zurich, Switzerland. 2014-08-24 - 2014-08-28. doi:10.1007/s00775-014-1159-9.


Cite as: http://hdl.handle.net/21.11116/0000-0007-A3AD-E
Abstract
Natural water oxidation, carried out by an inorganic Mn4CaO5 cluster embedded in the enzyme photosystem II of photosynthetic organisms, underpins all oxygenic life on earth [1]. Among the many poorly understood aspects of this process, which serves as the ultimate blueprint for synthetic efforts towards development of synthetic water splitting catalysts, is the role of calcium: why does the catalyst depend critically on calcium for its function, and why is natural water oxidation inhibited by very similar cations, even though they may be structurally incorporated in the catalytic cluster? We address these questions by combining recent results from spectroscopy (EPR/ENDOR), information from kinetics measurements, and extensive theoretical modelling of photosystem II and its oxygen evolving complex [1–4]. Our results suggest that the calcium ion satisfies not one but several diverse requirements, which are electronic as much as structural in nature. Most importantly, calcium simultaneously modulates the properties of not only the Mn4CaO5 cluster itself, but also of the redox-active tyrosine residue that mediates electron transfer from the water oxidation site to the photodriven charge separation site of the enzyme.