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

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 绿色植物和藻类几乎所有存在于大气中的氧气都是通过水的氧化产生的。这种需要光的反应是由与光系统II(PS II)相关的四个锰原子簇催化的。在我们正在进行的氧化态变化、结构以及与之相关的辅助因子钙和氯的研究中，我们广泛地使用了X射线吸收和EPR光谱。由于含Mn4团簇的膜缔合物在光吸收下被推进到其中间态(S态)，X射线吸收光谱表明，在S0和S1之间以及在S1和S2之间，Mn经历了氧化态的增加，但在S2和S3之间没有增加。后者的结论曾受到其他人的质疑，现在得到了一种新的、更明确的涉及锰钾荧光的X射线光谱分析的证实。我们利用一台独特的高分辨率X射线发射光谱仪进行了这项实验。本建议建立在过去实验的基础上，并解决了x射线发射光谱在PS II中的一些新的应用，如：a)K？发射光谱和位置选择光谱，它将选择性地探测Mn络合物中的不同的Mn位置或不同的氧化态，b)高分辨率的MnKa探测EXAFS，它将使我们能够收集超出Fe K边的EXAFS，从而提高分辨率，以及c)原子间的MnK？2，5光谱，这将成为Mn的配体原子的探针，特别是确定氯化物是否是PS II中的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.