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Biochemistry. 2013 Nov 5;52(44):7703-6. doi: 10.1021/bi401214v. Epub 2013 Oct 17.

S0-State model of the oxygen-evolving complex of photosystem II.

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Department of Chemistry, Yale University , New Haven, Connecticut 06511, United States.


The S0 → S1 transition of the oxygen-evolving complex (OEC) of photosystem II is one of the least understood steps in the Kok cycle of water splitting. We introduce a quantum mechanics/molecular mechanics (QM/MM) model of the S0 state that is consistent with extended X-ray absorption fine structure spectroscopy and X-ray diffraction data. In conjunction with the QM/MM model of the S1 state, we address the proton-coupled electron-transfer (PCET) process that occurs during the S0 → S1 transition, where oxidation of a Mn center and deprotonation of a μ-oxo bridge lead to a significant rearrangement in the OEC. A hydrogen bonding network, linking the D1-D61 residue to a Mn-bound water molecule, is proposed to facilitate the PCET mechanism.

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