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

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。大气中几乎所有的氧气都是由绿色植物和藻类通过水的氧化作用产生的。这种需要光的反应是由与光系统II （PS II）相关的四锰原子团催化的。在我们正在进行的氧化态变化、结构和相关辅因子Ca和Cl的研究中，我们广泛使用了x射线吸收和EPR光谱。当含有Mn4簇的膜相关络合物通过光吸收进入中间态（s态）时，x射线吸收光谱表明，Mn在S0和S1之间以及S1和S2之间的氧化态增加，而在S2和S3之间没有氧化态增加。后一个结论曾受到其他人的质疑，现在被一种新的、更确定的涉及Mn K荧光的x射线光谱学所证实。我们使用了一台独特的高分辨率x射线发射光谱仪来进行这个实验。本文在以往实验的基础上，提出了x射线发射光谱在PS II中Mn配合物中的一些新应用：a) K发射和位点选择光谱，可以选择性地探测Mn络合物中不同的Mn位点或不同的氧化态；b) EXAFS的高分辨率Mn Ka检测，将使我们能够收集Fe - K边缘以外的EXAFS，从而提高分辨率；c)原子间Mn K- 5光谱，将成为Mn配体原子的探针，特别是确定氯是否是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¿¿,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.