X-RAY SPECTROSCOPY OF PHOTOSYSTEM II SINGLE CRYSTALS

这个子项目是许多利用资源的研究子项目之一 由NIH/NCRR资助的中心拨款提供。子项目的主要支持 而子项目的主要调查员可能是由其他来源提供的， 包括其它NIH来源。 列出的子项目总成本可能 代表子项目使用的中心基础设施的估计数量， 而不是由NCRR赠款提供给子项目或子项目工作人员的直接资金。 光系统II（PS II）是存在于绿色植物和蓝藻中的一种膜结合蛋白复合物，它催化光合作用中的水氧化和放氧。反应中心专门叶绿素分子的单电子光氧化通过标记为S 0-S4的五个中间态与PS II中放氧复合物（OEC）对水的四电子氧化偶联。四个Mn原子的蛋白质结合复合物被认为是水氧化化学的位点，并在电荷积累中起作用。虽然这种锰络合物已经成为许多生物化学和光谱研究的主题，但络合物的确切结构和水氧化的机制仍然未知。虽然X-射线光谱方法可能是最翔实的技术，用于获得详细的信息的氧化态和周围的环境锰的OEC大多数的X-射线光谱研究进行随机取向的PS II膜，因此，没有角度依赖EXAFS功能观察。利用同步辐射的平面偏振性质的能力，使得研究取向PS II膜的二向色性成为可能，主要是在Mn？Mn载体在二-u-氧代和单-u-氧代桥接的Mn 2基序，已被证明是存在于OEC。在这个建议中，我们描述了实验与单晶锰模型化合物和光系统II。我们希望本研究将提供重要的见解锰络合物的结构和它的电子性质是至关重要的理解水的氧化和析氧的机制。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Photosystem II (PS II) is a membrane-bound protein complex found in green plants and cyanobacteria, which catalyzes photosynthetic water oxidation and oxygen evolution. Single-electron photo-oxidations of a specialized chlorophyll molecule in the reaction center are coupled to the four-electron oxidation of water by the oxygen-evolving complex (OEC) in PS II through five intermediate states labeled S0-S4. A protein-bound complex of four Mn atoms is thought to be the site of water oxidation chemistry and to function in charge accumulation. Although this Mn complex has been the subject of numerous biochemical and spectroscopic studies, the exact structure of the complex and the mechanism of water oxidation remain unknown. Although x-ray spectroscopic methods have been perhaps the most informative technique used to derive detailed information about the oxidation states of and the environment surrounding Mn in the OEC most of the x-ray spectroscopic studies were performed on randomly oriented PS II membranes; thus, no angle dependence of EXAFS features was observed. The ability to exploit the plane-polarized nature of synchrotron radiation has made possible the study of dichroism in oriented PS II membranes, mostly, in terms of the orientation dependence of the Mn?Mn vectors in the di-u-oxo and mono-u-oxo bridged Mn2 motifs that have been shown to be present in the OEC. In this proposal we describe experiments with single crystals of Mn model compounds and photosystem II. We expect the present study will provide important insights to the structure of the Mn complex and its electronic properties that are critical for understanding the mechanism of water oxidation and oxygen evolution.