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

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。 支持所有有氧生命的氧气在大气中是丰富的，因为它通过绿色植物、藻类和蓝藻的光合作用水氧化不断地再生。这种需要光的反应是由与光系统II(PS II)相关的Mn4Ca簇催化的。在我们正在进行的关于锰的氧化态变化、结构和相关的辅助因子钙和氯以及水氧化机理的研究中，我们正在使用BioCAT光束线进行X射线吸收和发射光谱实验，这是目前其他地方无法进行的。我们证明了扩展射程EXAFS方法的可行性，并在PS II样品中收集了不受铁干扰的数据。K空间数据和傅里叶变换的改进是显著的。我们现在可以分辨出S(下标)1和S(下标)2态中的两个很短的Mn-Mn距离；而以前我们只能分辨出一个~2.7o的距离。我们还利用定向PS II膜收集了射程扩展的EXAFS数据，很明显，非均质性更加明显。这些结果提供了关于水氧化锰络合物结构的重要信息，这些结果发表在J.Biol上。化学。本刊被选为本周最佳报纸，并附有封面图片。我们将这些研究推广到酶周期的S(下标)0和S(下标)3中间态，初步结果表明，在S(下标)3态中，锰配合物的结构发生了显著变化。这一结果对在水氧化反应的众多机理中进行选择具有重要意义。

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.