HIGH RESOLUTION MN X-RAY FLUORESCENCE SPECTROSCOPY OF THE OXYGEN-EVOLVING COMPLE

该子项目是利用该技术的众多研究子项目之一 资源由 NIH/NCRR 资助的中心拨款提供。子项目和 研究者 (PI) 可能已从 NIH 的另一个来源获得主要资金， 因此可以在其他 CRISP 条目中表示。列出的机构是 对于中心来说，它不一定是研究者的机构。 绿色植物和藻类通过水的氧化产生几乎所有存在于大气中的氧气。这种需要光的反应由与光系统 II (PS II) 相关的四锰原子簇催化。在我们对氧化态变化、结构和相关辅因子 Ca 和 Cl 的持续研究中，我们广泛使用了 X 射线吸收和 EPR 光谱。当含有 Mn4 簇的膜缔合复合物通过光吸收前进通过其中间态（S 态）时，X 射线吸收光谱表明 Mn 在 S0 和 S1 之间以及 S1 和 S2 之间经历氧化态增加，但在 S2 和 S3 之间则不增加。后一个结论曾受到其他人的质疑，现在已被涉及 Mn K 荧光的新的、更明确的 X 射线光谱证实。我们利用独特的高分辨率 X 射线发射光谱仪来进行该实验。本提案建立在过去的实验基础上，解决了 X 射线发射光谱在 PS II 中 Mn 配合物中的一些新应用，如下：a) K¿ 发射和位点选择性光谱，将选择性地探测 Mn 配合物中的不同 Mn 位点或不同氧化态，b) EXAFS 的高分辨率 Mn Ka 检测，这将使我们能够收集超出 Fe K 边缘的 EXAFS，从而提高分辨率，c) 原子间 Mn K¿2,5 光谱，它将成为 Mn 配体原子的探针，特别是确定氯化物是否是 PS II 中 Mn 的配体。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Green plants and algae generate almost all of the oxygen present in the atmosphere by the oxidation of water. This light-requiring reaction is catalyzed by a four-manganese atom cluster associated with Photosystem II (PS II). In our ongoing investigations of the oxidation-state changes, the structure and the associated cofactors Ca and Cl, we have made extensive use of x-ray absorption and EPR spectroscopy. As the membrane-associated complex containing the Mn4 cluster is advanced through its intermediate states (S-states) by light absorption, x-ray absorption spectroscopy indicates that Mn undergoes an increase in oxidation state between S0 and S1 and between S1 and S2 but not between S2 and S3. This latter conclusion, which had been questioned by others, is now confirmed by a new and more definitive x-ray spectroscopy involving Mn K¿ fluorescence. We made use of an unique high-resolution x-ray emission spectrometer to carry out this experiment. The present proposal builds on the past experiments and addresses some new applications of x-ray emission spectroscopy to the Mn complex in PS II as follows: a) K¿ emission and site selective spectroscopy that will selectively probe different Mn sites or different oxidation states in the Mn complex, b) High resolution Mn Ka detection of EXAFS that will allow us to collect EXAFS beyond the Fe K-edge thus improving resolution and c) Interatomic Mn K¿2,5 spectra that will be a probe for the ligand atoms of Mn, especially to ascertain whether chloride is a ligand of Mn in PS II.