Calcium EXAFS establishes the Mn-Ca cluster in the oxygen-evolving complex of photosystem II

Authors :: Vittal K. Yachandra
Shelly A. Pizarro
Junko Yano
Karen L. McFarlane Holman
Emanuele Bellacchio
Kenneth Sauer
John H. Robblee
Roehl M. Cinco
Source :: Cinco, Roehl M.; Holman, Karen L. McFarlane; Robblee, John H.; Yano, Junko; Pizarro, Shelly A.; Bellacchio, Emanuele; et al.(2002). Calcium EXAFS establishes the Mn-Ca cluster in the oxygen-evolving complex of Photosystem II. Biochemistry, 41(43). Lawrence Berkeley National Laboratory: Lawrence Berkeley National Laboratory. Retrieved from: http://www.escholarship.org/uc/item/3pk3m09p
Publication Year :: 2002
Abstract: The proximity of Ca to the Mn cluster of the photosynthetic water-oxidation complex is demonstrated by X-ray absorption spectroscopy. We have collected EXAFS data at the Ca K-edge using active PS II membrane samples that contain approximately 2 Ca per 4 Mn. These samples are much less perturbed than previously investigated Sr-substituted samples, which were prepared subsequent to Ca depletion. The new Ca EXAFS clearly shows backscattering from Mn at 3.4 angstroms, a distance that agrees with that surmised from previously recorded Mn EXAFS. This result is also consistent with earlier related experiments at the Sr K-edge, using samples that contained functional Sr, that show Mn is {approx}; 3.5 angstroms distant from Sr. The totality of the evidence clearly advances the notion that the catalytic center of oxygen evolution is a Mn-Ca heteronuclear cluster.

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