MANGANESE OXYGEN-EVOLVING COMPLEX: STRUCTURE/FUNCTION

描述：（改编自申请人摘要）含Mn的金属蛋白 在氧化还原活性作用中参与多种生理学上重要的 涉及分子氧代谢的反应。其中包括： 将超氧化物自由基解毒为O（2）和过氧化物的超氧化物歧化酶， 一种过氧化氢酶，能将过氧化物还原为O（2）和H（2）O，一种核糖核苷酸 还原酶，催化脱氧核糖核苷酸的合成，也许是最 复杂且重要的是，含Mn的放氧复合物（Mn-OEC）， 参与光系统II中水氧化成分子氧。 支持所有有氧生物的氧气在大气中很丰富， 通过Mn-OEC的光合作用水氧化，其不断再生。 光诱导水氧化为分子氧是其中最重要的一种 在生物圈中如此大规模地发生的化学过程。 光合水氧化涉及四个电子的去除，在一个 逐步的方式通过光诱导氧化，从两个水分子的 Mn-OEC产生一个氧分子。需要解决的核心问题 解决和本建议的总体目标如下：1） 确定Mn在四种中间态或S态的氧化态，2） 表征氧桥四核锰配合物的结构变化 随着它通过酶循环的进展，3）确定水的机制 氧化和氧释放，4）阐明结构和功能作用 必需辅因子C1（-）和Ca（2+）。 X射线吸收光谱（XAS）与电子 顺磁共振（EPR）在我们的理解中发挥了重要作用 O（2）进化的结构和机制方面。氧化 锰的状态和锰络合物的结构变化，因为它的进展 通过X射线吸收光谱法测定 使用通过EPR光谱表征的样品。氧化态是 通过Mn K-和L-边缘光谱和高分辨率X射线测定 荧光光谱法对中间体的结构进行了表征 通过XAS使用通过闪光照明制备的样品。辅助因子的作用 Ca（2+）和C1（-）Br（-）通过Ca（Sr）和C1（Br）K边XAS寻址 分别

DESCRIPTION: (Adapted from applicant's abstract) Metalloproteins containing Mn in a redox active role are involved in a variety of physiologically important reactions involving dioxygen metabolism. These include, amongst others, a superoxide dismutase that detoxifies superoxide radicals to O(2) and peroxide, a catalase that disproportionates peroxide to O(2) and H(2)O, a ribonucleotide reductase that catalyzes synthesis of deoxyribonucleotide, and perhaps the most complex and important, the Mn-containing oxygen-evolving complex (Mn-OEC) that is involved in the oxidation of water to dioxygen in Photosystem II. Oxygen, which supports all aerobic life, is abundant in the atmosphere because of its constant regeneration by photosynthetic water oxidation by the Mn-OEC. The light-induced oxidation of water to dioxygen is one of the most important chemical process4es occurring on such a large scale in the biosphere. Photosynthetic water oxidation involves removal of four electrons, in a stepwise manner by light-induced oxidation, from two water molecules by the Mn-OEC to produce a molecule of oxygen. Central questions that need to be resolved and the overall objective of this proposal are as follows: 1) Determine the oxidation states of Mn in the four intermediate or S-states, 2) Characterize the structural changes of the oxo-bridged tetranuclear Mn complex as it advances through the enzymatic cycle, 3) Determine the mechanism of water oxidation and oxygen evolution, 4) Elucidate the structural and functional role of the essential cofactors C1(-) and Ca(2+). The interplay between X-ray absorption spectroscopy (XAS) and Electron paramagnetic resonance (EPR) has played an essential role in our understanding of the structural and mechanistic aspects of O(2) evolution. The oxidation states of Mn and the structural changes of the Mn complex as it advances through the enzymatic cycle are determined by X-ray absorption spectroscopy using samples characterized by EPR spectroscopy. The oxidation states are determined by Mn K- and L-edge spectroscopy, and high resolution X-ray fluorescence spectroscopy. The structure of the intermediates are characterized by XAS using samples prepared by flash illumination. The role of cofactors Ca(2+) and C1(-) Br(-) is addressed by Ca (Sr) and C1 (Br) K-edge XAS respectively.