HIGH RESOLUTION MN X-RAY EMISSION SPECTROSCOPY OF THE OXYGEN-EVOLVING COMPLEX

该子项目是利用 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。列出的机构是 中心，不一定是研究者的机构。 氧气，支持所有的有氧生命，在大气中是丰富的，因为它不断再生的光合作用水氧化的绿色植物，藻类和蓝藻。该光反应由与光系统II（PS II）相关的Mn 4Ca簇催化。在我们正在进行的Mn氧化态变化、结构和相关辅因子Ca和Cl以及水氧化机制的研究中，我们正在使用BioCAT光束线进行目前在其他地方不可能进行的X射线吸收和发射光谱实验。我们已经证明了扩展范围EXAFS方法的可行性，并收集了PS II样品中没有Fe干扰的数据。k空间数据和傅立叶变换的改进是惊人的。我们现在可以分辨出S（下标）1和S（下标）2态的两个短的Mn-Mn距离，而以前我们只能分辨出一个约2.7 <$m的距离。我们还收集了扩展范围的EXAFS数据使用定向PS II膜，它是相当明显的，异质性更明显。这些结果提供了有关水氧化锰络合物结构的重要信息，已在《生物化学杂志》上发表，该出版物已被选为本周的论文，并附有封面图。我们将这些研究扩展到了酶循环的S（下标）0和S（下标）3中间态，初步结果表明，在S（下标）3态下Mn配合物的结构发生了显著的变化。这一结果具有重要的意义，选择之间的许多机制，已提出的水氧化反应。

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. Oxygen, that supports all aerobic life, is abundant in the atmosphere because of its constant regeneration by photosynthetic water oxidation by green plants, algae, and cyanobacteria. This light-requiring reaction is catalyzed by a Mn4Ca cluster associated with photosystem II (PS II). In our ongoing investigations of the Mn oxidation-state changes, the structure and the associated cofactors Ca and Cl and the mechanism of water oxidation, we are using the BioCAT beamline to conduct X-ray absorption and emission spectroscopy experiments that are at present not possible elsewhere. We have shown the feasibility of the range-extended EXAFS method and collected data without interference from Fe in the PS II sample. The improvement in the k-space data and the Fourier transform is striking. We can now resolve two short Mn-Mn distances in the S (subscript)1 and S (subscript)2 states; while earlier we could discern only one distance of ~2.7 ¿. We have also collected range-extended EXAFS data using oriented PS II membranes, and it is quite clear that the heterogeneity is more obvious. These results which provide important information about the structure of the water oxidizing Mn complex are in press in J. Biol. Chem. and this publication has been selected as the paper of the week with a cover figure. We have extended these studies to the S (subscript)0 and S (subscript)3 intermediate states of the enzymatic cycle, and the preliminary results show that there is a significant change in the structure of the Mn complex in the S (subscript)3 state. This result has important implications for choosing between the many mechanisms that have been proposed for the water oxidation reaction.