X-RAY SPECTROSCOPIC STUDIES ON HEME-COPPER OXIDASES

描述：血红素-铜氧化物酶的功能是连接氧气的能量。 呼吸过程中还原为三磷酸腺苷的合成。因此，这些氧化还原 酶在有氧代谢中起着关键作用。氧化还原过程发生 在构成酶和酶的活性中心的金属中心 容易被氰化物、一氧化碳等小分子抑制 以及其他有毒物质，往往会带来致命的后果。理解 金属中心的配位化学是 阐明呼吸和能量转导的详细机制 在细胞内。最近发表的晶体结构定义了 金属中心的协调已经解决了一些老问题 争议，但也提出了新的、更耐人寻味的问题 这只能通过聚焦良好的光谱实验来解决。这 一项提案寻求资金，将X射线吸收光谱(XAS)应用于 本报告强调了若干重要的结构性和机械性问题 晶体结构数据。拟议的研究利用了独特的 XAS对进一步细化金属离子配位的灵敏度 氧化酶，并首次探讨了其与酶的配位作用 还原酶和催化中间体P和F。 这些实验将被用来测试“组氨酸”的有效性 一种最近提出的质子泵送机制。建议数 研究还将详细调查#年CUA中心的结构。 可溶性亚基II片段，以及在一些工程中 通过“循环导向”诱变制备的构建体。这些实验 从EXAFS初步确定唯一的2.34A铜-铜 CUA中的交互作用。还计划进行其他实验，以探索 两种新型血红素-铜氧化物酶--一氧化氮的金属中心配位作用 还原酶和天青酶。

DESCRIPTION: Heme-copper oxidases function to couple the energy of oxygen reduction to ATP synthesis in the process of respiration. Thus, these redox enzymes play pivotal roles in aerobic metabolism. The redox processes occur at the metal centers which constitute the active sites of the enzymes and are easily inhibited by small molecules such as cyanides, carbon monoxide and other toxic substances, often with fatal consequences. Understanding the coordination chemistry of the metal centers is a critical step in elucidating the detailed mechanism of respiration and energy transduction within the cell. The recent publication of crystal structures that define the coordination of the metal centers has settled a number of old controversies but has also raised new and even more intriguing questions that can only be addressed by well-focused spectroscopic experiments. This proposal seeks funding to apply X-ray absorption spectroscopy (XAS) to a number of important structural and mechanistic questions highlighted by the crystal structural data. The proposed studies utilize the unique sensitivity of XAS to refine further the metal ion coordination in the oxidized enzyme, and to probe for the first time the coordination present in the reduced enzyme and the catalytic intermediates P and F. The results of these experiments will be used to test the validity of the "histidine cycle,' a recently proposed mechanism for proton pumping. The proposed studies will also investigate in detail the structure of the CuA center in the soluble subunit II fragment, as well as in a number of engineered constructs prepared by "loop-directed" mutagenesis. These experiments follow on from the initial determination from EXAFS of a unique 2.34 A Cu-Cu interaction in CuA. Other experiments are planned that will explore the metal-site coordination in two novel heme-copper oxidases, nitric oxide reductase and azurin oxidase.