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

该子项目是利用该技术的众多研究子项目之一 资源由 NIH/NCRR 资助的中心拨款提供。子项目和 研究者 (PI) 可能已从 NIH 的另一个来源获得主要资金， 因此可以在其他 CRISP 条目中表示。列出的机构是 对于中心来说，它不一定是研究者的机构。 支持所有有氧生命的氧气在大气中含量丰富，因为绿色植物、藻类和蓝细菌通过光合水氧化不断再生氧气。这种需光反应由与光系统 II (PS II) 相关的 Mn4Ca 簇催化。在我们正在进行的对 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，我们使用 BioCAT 光束线进行 X 射线吸收和发射光谱实验，这在其他地方目前是不可能的。我们展示了扩展 EXAFS 方法的可行性，并在不受 PS II 样品中 Fe 干扰的情况下收集了数据。 k 空间数据和傅里叶变换的改进是惊人的。我们现在可以解析 S（下标）1 和 S（下标）2 状态下的两个短 Mn-Mn 距离；而早些时候我们只能辨别大约 2.7 ¿ 的距离。我们还使用定向 PS II 膜收集了范围扩展的 EXAFS 数据，很明显，异质性更加明显。这些结果提供了有关水氧化锰配合物结构的重要信息，发表在 J. Biol 上。化学。该出版物已被选为带封面图的本周论文。我们将这些研究扩展到酶循环的S(下标)0和S(下标)3中间态，初步结果表明，S(下标)3态下Mn配合物的结构发生了显着的变化。这一结果对于在水氧化反应提出的多种机制之间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.