Rapid Evolution of the Photosystem II Electronic Structure During Water Splitting
Journal Article - Open Access
NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON United States
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Photosynthetic water oxidation is a fundamental process that sustains the biosphere. A Mn4Ca cluster embedded in the photosystem II protein environment is responsible for the production of atmospheric oxygen. Here, time-resolved x-ray emission spectroscopy XES is used to observe the process of oxygen formation in real time. These experiments reveal that the oxygen evolution step, initiated by three sequential laser flashes, is accompanied by rapid within 50 mu s changes to the Mn K beta XES spectrum. However, no oxidation of the Mn4Ca core above the all-Mn-IV state is detected to precede O-O bond formation, and the observed changes are therefore assigned to O-O bond-formation dynamics. We propose that O-O bond formation occurs prior to the transfer of the final fourth electron from the Mn4Ca cluster to the oxidized tyrosine TyrZ residue. This model resolves the kinetic limitations associated with O-O bond formation and suggests an evolutionary adaptation to avoid releasing harmful peroxide species.
- Atomic and Molecular Physics and Spectroscopy