EPR & Optical Studies of Photosynthetic Water Oxidation

EPR

基本信息

批准号：
6938564
负责人：
RICHARD J DEBUS
金额：
$ 17.84万
依托单位：
UNIVERSITY OF CALIFORNIA RIVERSIDE
依托单位国家：
美国
项目类别：
财政年份：
2002
资助国家：
美国
起止时间：
2002-08-01 至 2007-07-31
项目状态：
已结题

来源：
https://reporter.nih.gov/project-details/6938564
关键词：
affinity chromatography chlorophyll electron spin resonance spectroscopy electron transport enzyme mechanism enzyme substrate complex isozymes manganese metalloenzyme oxidation oxidation reduction reaction photosynthesis photosynthetic reaction centers photosystem site directed mutagenesis spectrometry tyrosine water

项目摘要

DESCRIPTION (provided by applicant): The project's overall goal is to describe the molecular mechanism of photosynthetic water oxidation. The catalytic site is located in Photosystem II (PSII) and contains a (Mn)4-Ca cluster that interacts with a redox-active tyrosine residue known as Yz. The Yz radical extracts electrons and protons from the (Mn)4-Ca cluster, leading to the oxidation of water and the release of 02 as a by-product. The project's specific goals are to characterize the substrate, inhibitor, and cofactor binding properties of the (Mn)4 cluster in its dark-stable S1 oxidation state and to further characterize the environmental factors that control the reactivity of tyrosine Yz. These objectives build on our recent discoveries that (1) the (Mn)4 cluster in its S1 oxidation state exhibits a parallel polarization multiline EPR signal, and (2) the rate of electron transfer from YD to P680+ is five orders of magnitude faster than previously believed (YD, a second redox-active tyrosine in PSII, does not participate in the primary electron transfer reactions of water oxidation). The proposed studies will exploit the S1 state multiline EPR signal as a spectroscopic probe of the (Mn)4 cluster in its S1 oxidation stale in the same manner that the S2 state multiline EPR signal has been exploited over the last two decades as a probe of the (Mn)4 cluster in its S2 oxidation state. Our observation that electron transfer from YD to P680+ takes place rapidly has important mechanistic implications and suggests a variety of hypotheses regarding the factors that govern the reactivity of tyrosine Yz and, possibly, the factors that govern location of the P680+ cation among the chlorophyll molecules that constitute P680. The proposed studies will test these hypotheses. Understanding the mechanism of photosynthetic water oxidation should provide insight into the mechanisms of two important classes of enzymes that are currently the subjects of intensive bio-medical research: metallo-radical enzymes and enzymes whose mechanisms involve proton-coupled electron transfer reactions. Photosystem II possesses unique advantages for studying the initiation of catalysis in these two classes of enzymes because catalysis in PSII can be initiated with a flash of light, thereby facilitating kinetic studies of reaction cycle intermediates with high time resolution.

描述（由申请人提供）：该项目的总体目标是描述光合作用水氧化的分子机制。催化位点位于光系统II（PSII）中，并包含一个（MN）4-CA簇，该簇与称为Yz的氧化还原活性酪氨酸残基相互作用。 Yz自由基提取物从（MN）4-Ca簇中的电子和质子导致水的氧化并释放02作为副产品。该项目的具体目标是表征（Mn）4簇在其深稳定的S1氧化态中的底物，抑制剂和辅因子结合特性，并进一步表征控制酪氨酸Yz反应性的环境因素。 These objectives build on our recent discoveries that (1) the (Mn)4 cluster in its S1 oxidation state exhibits a parallel polarization multiline EPR signal, and (2) the rate of electron transfer from YD to P680+ is five orders of magnitude faster than previously believed (YD, a second redox-active tyrosine in PSII, does not participate in the primary electron transfer reactions of water oxidation).拟议的研究将利用S1状态多行EPR信号作为其S1氧化阶段（Mn）4簇的光谱探针，其方式与过去的二十年中S2状态多行EPR信号相同，作为在其S2氧化状态中的（MN）4簇的探针。我们观察到电子从YD转移到P680+的转移迅速发生具有重要的机械意义，并提出了有关控制酪氨酸Yz的反应性以及控制P680+阳离子位置的因素的各种假设，这些因素可能是构成P680构成P680的叶绿体分子中的位置。拟议的研究将检验这些假设。了解光合作用水氧化的机制应提供有关目前是强化生物医学研究主题的两种重要类酶的机制：金属激进酶和酶，它们的机制涉及质子耦合的电子转移反应。光系统II具有研究这两类酶开始催化的独特优势，因为PSII中的催化可以用光闪烁来启动，从而促进了与高时间分辨率的反应循环中间体的动力学研究。