Light-induced water splitting and oxygen release is performed by a Mn4O5Ca cluster in photosystem II of all organisms performing oxygenic photosynthesis. A 1.9� resolution X-ray structure was recently published (1). We report cw/pulse EPR, ENDOR and ELDOR-detected NMR experiments performed on the paramagnetic S0 and S2 states of the cluster and related models (2). Differences between PSII from higher plants and cyanobacteria (3) and the effect of Ca2+ removal and Ca2+/Sr2+ exchange (4) are presented. Furthermore, the binding of water is probed using 2H2O and H217O samples. A robust model for the Mn4O5Ca cluster is obtained with important implications for the enzymatic mechanism (5).(1) Y. Umena et al. Nature 2011  , 473, 55(2) N. Cox et. al. Inorg. Chem. 2011  , 50, 8238(3) J.H. Su et al. BBA 2011,  1807, 829(4) N. Cox et al. JACS 2011  , 133, 3635(5) W. Ames et al. JACS 2011  , in press

Water binding and water splitting in photosystem II probed by high frequency multinuclear EPR, ENDOR and ELDOR-detected NMR

243rd National Meeting (2012)

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