Calcium EXAFS Establishes the Mn-Ca Cluster in the Oxygen-Evolving Complex of Photosystem II
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- 作者：Roehl M. Cinco ; Karen L. McFarlane Holman ; John H. Robblee ; Junko Yano ; Shelly A. Pizarro ; Emanuele Bellacchio ; Kenneth Sauer ; and Vittal K. Yachandra
- 刊名：Biochemistry
- 出版年：2002
- 出版时间：October 29, 2002
- 年：2002
- 卷：41
- 期：43
- 页码：12928 - 12933
- 全文大小：73K
- 年卷期：v.41,no.43(October 29, 2002)
- ISSN：1520-4995
文摘
The proximity of Ca to the Mn cluster of the photosynthetic water-oxidation complex isdemonstrated by X-ray absorption spectroscopy. We have collected EXAFS data at the Ca K-edge usingactive PS II membrane samples that contain approximately 2 Ca per 4 Mn. These samples are much lessperturbed than previously investigated Sr-substituted samples, which were prepared after Ca depletion.The new Ca EXAFS clearly shows backscattering from Mn at 3.4 Å, a distance that agrees with thatsurmised from previously recorded Mn EXAFS. This result is also consistent with earlier related experimentsat the Sr K-edge, using samples that contained functional Sr, that show Mn is ~3.5 Å distant from Sr.The totality of the evidence clearly advances the notion that the catalytic center of oxygen evolution is aMn-Ca heteronuclear cluster.