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Light-induced water oxidation in photosynthesis

MPS-Authors
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Lubitz,  Wolfgang
Research Department Lubitz, 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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Rapatskiy,  Leonid
Research Department Lubitz, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Lohmiller,  Thomas
Research Department Lubitz, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Pérez Navarro,  Montserrat
Research Department Lubitz, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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

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Pantazis,  Dimitrios A.
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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Citation

Lubitz, W., Cox, N., Rapatskiy, L., Lohmiller, T., Pérez Navarro, M., Ames, W., et al. (2013). Light-induced water oxidation in photosynthesis. Poster presented at XVIth International Conference on Biological Inorganic Chemistry, Grenoble, France.


Cite as: http://hdl.handle.net/21.11116/0000-0007-A2D4-2
Abstract
Light-induced water oxidation in photosynthesis occurs in a single biological supercomplex called photosystem II at a protein-bound Mn4O5Ca cluster, which passes through 5 intermediate states (Si-state cycle). (1) A detailed electronic model of the catalytic center has been developed based on structural data from X-ray crystallography (2) and magnetic resonance (EPR and ENDOR) techniques. (3-6) Based on 55Mn ENDOR spin and oxidation states of the Mn ions and the coupling between them could be determined; together with chemical modifications of the cluster a model of the catalytic center has been obtained. High field ELDOR-detected NMR (EDNMR) at 94GHz (see figure) is applied to detect the interaction of the cluster (S2 state) with magnetic nuclei of amino acids (14N) and attached water molecules. In samples exchanged with H217O, 17O hyperfine couplings of three different types of water molecules were detected, (6) see figure. They could be assigned based on the structural model from X-ray crystallography (2) which has been refined using densitiy functional theory (5) and comparison with model complexes. Additional experiments like Ca/Sr exchange (4) and the use of inhibitors (NH3) (7) helped in this endeavor. These data further refine the reaction pathway fpr O-O bond formation supporting an oxo/oxyl coupling mechanism in the catalytically active state (S4) of the cycle. (8,1) A mechanistic model for water oxidation in photosynthesis is proposed.