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Photosynthesis Research

, Volume 92, Issue 3, pp 275–287

First Online: 19 January 2007Received: 06 October 2006Accepted: 08 December 2006


Oxidation of H2O by photosystem II is a unique redox reaction in that it requires Ca as well as Cl as obligatory activators-cofactors of the reaction, which is catalyzed by Mn atoms. The properties of the binding site for Ca in this reaction resemble those of other Ca binding proteins, and recent X-ray structural data confirm that the metal is in fact ligated at least in part by amino acid side chain oxo anions. Removal of Ca blocks water oxidation chemistry at an early stage in the cycle of redox reactions that result in O-O bond formation, and the intimate involvement of Ca in this reaction that is implied by this result is confirmed by an ever-improving set of crystal structures of the cyanobacterial enzyme. Here, we revisit the photosystem II Ca site, in part to discuss the additional information that has appeared since our earlier review of this subject van Gorkom HJ, Yocum CF In: Wydrzynski TJ, Satoh K eds Photosystem II: the light-driven water:plastoquinone oxidoreductase, and also to reexamine earlier data, which lead us to conclude that all S-state transitions require Ca.

KeywordsCalcium Photosystem II Oxygen evolution S-states Thermoluminescence AbbreviationsChlChlorophyll

EDTAEthylenediaminetetraacetic acid

EGTAEthylene glycol bis2-aminoethyl ether-N,N,N′, N′-tetraacetic acid

EXAFSExtended X-ray absorption fine structure

FT-IRFourier transform infrared

OECOxygen-evolving complex


PsbOThe 33 kDa extrinsic protein

PsbPThe 23 kDa extrinsic protein

PsbQThe 17 kDa extrinsic protein


XANESX-ray absorption near-edge structure

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Autor: M. Miqyass - H. J. van Gorkom - C. F. Yocum


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