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Photosynthetic O2 Formation Tracked by Time-Resolved X-ray Experiments
M. Haumann,*P. Liebisch,C. Müller,M. Barra,M. Grabolle,H. Dau*
Plants and cyanobacteria produce atmospheric dioxygen from water,powered by sunlight and catalyzed by a manganese complex inphotosystem II. A classic S-cycle model for oxygen evolutioninvolves five states, but only four have been identified. Themissing S4 state is particularly important because it is directlyinvolved in dioxygen formation. Now progress comes from an x-raytechnique that can monitor redox and structural changes in metalcenters in real time with 10-microsecond resolution. We showthat in the O2-formation step, an intermediate is formedtheenigmatic S4 state. Its creation is identified with a deprotonationprocess rather than the expected electron-transfer mechanism.Subsequent electron transfer would give an additional S4' state,thus extending the fundamental S-state cycle of dioxygen formation.
Freie Universität Berlin, FB Physik, Arnimallee 14, D-14195 Berlin, Germany
* To whom correspondence should be addressed. E-mail: haumann{at}physik.fu-berlin.de (M.H.); holger.dau{at}physik.fu-berlin.de (H.D.)
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James E. Penner-Hahn and Charles F. Yocum (11 November 2005) Science310 (5750), 982.
[DOI: 10.1126/science.1120919] |Summary »|Full Text »|PDF »
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