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的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 绿色植物和藻类通过水的氧化产生了大气中几乎所有的氧气。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。在我们正在进行的调查的氧化状态的变化，结构和相关的辅因子Ca和Cl，我们已经广泛使用的X射线吸收和EPR光谱。由于含有Mn 4簇的膜缔合络合物通过光吸收通过其中间态（S-态）而被推进，X射线吸收光谱表明Mn在S 0和S1之间以及在S1和S2之间经历氧化态的增加，但在S2和S3之间不经历氧化态的增加。后一个结论，这已被其他人质疑，现在证实了一个新的和更明确的x射线光谱，涉及锰钾荧光。我们利用独特的高分辨率X射线发射光谱仪进行了这项实验。本提案建立在过去的实验基础上，并提出了X射线发射光谱在PS II中Mn络合物的一些新应用，如下所示：发射和位置选择光谱学，其将选择性地探测Mn络合物中的不同Mn位置或不同氧化态，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，以及c）原子间Mn K？2，5光谱，这将是Mn的配体原子的探针，特别是为了确定氯化物是否是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.