MANGANESE OXYGEN-EVOLVING COMPLEX: STRUCTURE/FUNCTION

描述：(摘自申请者摘要)含锰的金属蛋白 在氧化还原过程中起着积极作用，参与了多种重要的生理过程 涉及氧气代谢的反应。其中包括一项 能将超氧阴离子自由基解毒为O(2)和过氧化氢的超氧化物歧化酶， 一种过氧化氢酶，使过氧化氢不成比例地生成O(2)和H(2)O，一种核糖核苷酸 催化合成脱氧核糖核苷酸的还原酶，可能是 复杂而重要的是，含锰放氧络合物(Mn-OEC) 参与了光系统II中水被氧化为氧气的过程。 支持所有有氧生命的氧气在大气中非常丰富，因为 其持续再生的光合作用水氧化的锰-OEC。 光诱导水氧化成氧气是最重要的反应之一 在生物圈中发生如此大规模的化学过程。 光合作用的水氧化包括在一个 通过光诱导氧化的方式，从两个水分子 锰-OEC产生氧分子。需要解决的核心问题 本提案的决议和总体目标如下：1) 测定四种中间态或S态中锰的氧化态，2) 氧桥联四核锰配合物的结构变化表征 当它在酶循环中前进时，3)确定水的机制 氧化和放氧，4)阐明其结构和功能作用 必需辅因子C_1(-)和C_(2+)。 X射线吸收光谱(XAS)与电子的相互作用 顺磁共振(EPR)在我们的理解中起着至关重要的作用 O(2)演化的结构和机制方面。氧化 锰的状态和锰络合物在推进过程中的结构变化 通过酶循环的X射线吸收光谱测定 利用EPR波谱对样品进行表征。氧化态是 用MnK和L边缘能谱和高分辨X射线测定 荧光光谱学对中间体的结构进行了表征 用闪光照射制备的样品进行XAS分析。辅因子的作用 钙(2+)和氯(-)溴(-)由钙(锶)和氯(溴)K边XAS寻址 分别进行了分析。

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.