FTIR Studies of Photosynthetic Oxygen Evolution

描述(申请人提供)：该项目的总体目标是阐明光合作用放氧的分子机制。这一过程发生在光系统II中，是几乎所有大气氧气的来源。催化中心包含一个(Mn)4-Ca簇，它与氧化还原活性酪氨酸残基YZ相互作用。YZ(自由基)从(Mn)4-Ca团簇中提取电子和质子，导致水的氧化和氧的释放。该项目的主要目标是描述在催化循环的各个步骤中伴随着(Mn)4-Ca簇氧化的结构变化。这些信息对理解放氧机制至关重要，并将补充从X射线结晶学获得的信息。主要的研究工具将是傅里叶变换红外(FTIR)差分光谱。该项目的具体目标是：(1)确定在催化循环的各个步骤中经历氧化的特定锰离子(S)；(2)确定作为促进(Mn)4-Ca簇合物在催化循环中质子偶联氧化的关键碱基的氨基酸残基；(3)表征氧气形成反应的最终中间体，这是一种可以通过提高环境氧压来捕获的中间体；(4)使用经修改的细菌反应中心作为模型系统，以表征连接的金属离子在其氧化过程中环境发生的变化；(5)利用近红外激发共振拉曼光谱作为表征(Mn)4-Ca团簇环境的辅助工具。除了提供对光合作用放氧机制的基本见解外，该项目还将深入了解金属酶和酶的机制，其机制涉及质子耦合电子转移(PCET)反应。这类酶催化线粒体中的生物能量传递。阐明这些酶的催化机制对于了解线粒体疾病和衰老的分子基础是必不可少的。光系统II既是金属酶的一个很好的例子，也是研究质子耦合电子转移反应的独特实验室。它的优势来自于它能够通过单次闪光完成催化循环，从而促进了高时间分辨率的反应循环中间体的动力学研究。

DESCRIPTION (provided by applicant): The project's overall goal is to elucidate the molecular mechanism of photosynthetic oxygen evolution. This process takes place in Photosystem II and is the source of nearly all atmospheric oxygen. The catalytic site 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 oxygen. The project's primary goal is to characterize the structural changes that accompany the oxidation of the (Mn)4-Ca cluster during the individual steps of the catalytic cycle. This information is crucial to understanding the mechanism of oxygen evolution and will complement the information that is being obtained from X-ray crystallography. The primary investigative tool will be Fourier transform infrared (FTIR) difference spectroscopy. The project's specific aims are: (1) To identify the specific Mn ion(s) that undergo oxidation during the individual steps in the catalytic cycle; (2) To identify the amino acid residues that serve as the critical bases that facilitate the proton-coupled oxidations of the (Mn)4-Ca cluster during the catalytic cycle; (3) To characterize the final intermediate of the oxygen formation reaction, an intermediate that can be trapped by increasing the ambient oxygen pressure; (4) To employ modified bacterial reaction centers as model systems for characterizing changes that occur in the environment of a ligated metal ion in response to its oxidation; (5) To employ near-infrared excitation resonance Raman spectroscopy as an additional tool for characterizing the environment of the (Mn)4-Ca cluster. In addition to providing fundamental insight into the mechanism of photosynthetic oxygen evolution, the project will provide insight into the mechanisms of metalloradical enzymes and enzymes whose mechanisms involve proton-coupled electron transfer (PCET) reactions. Such enzymes catalyze biological energy transduction in mitochondria. Elucidating the catalytic mechanisms of these enzymes is essential for understanding the molecular basis of mitochondrial diseases and aging. Photosystem II is both an excellent example of a metalloradical enzyme and a unique laboratory for studying proton-coupled electron transfer reactions. Its advantages derive from its ability to be stepped through its catalytic cycle with single flashes of light, thereby facilitating kinetic studies of reaction cycle intermediates with high time resolution.