Determining the structural basis for the mechanism of catalytic O2 evolution by t

描述(由申请人提供)：通常称为亚氯酸盐歧化酶(CLD)的含血红素的酶催化亚氯酸盐离子ClO2-的单分子分解，如方案1所示。该反应被认为是通过血红素催化的O-键亚氯酸盐FeIClO2-异构化为配位的过氧次氯酸盐而形成化合物I(2)。 FeIII-OOCL-(3)，随后发生分子内氧化还原反应，释放O2和Cl-。 最近的光谱和动力学工作表明，催化机理是通过具有化合物I(CPD-I)特性的两电子氧化的血红素中间体进行的。它的形成被认为是随着两电子还原片段次氯酸盐的释放而发生的，次氯酸盐与CPD-I的基氧原子重新结合产生过氧次氯酸盐络合物。 该络合物对O2和Cl-的释放不稳定。放出O2的反应在生物学上很少见，另一个已知的例子是由PSII的放氧四核Mn簇催化的反应。CLD中间体的确切性质以及酶对其反应活性的调节仍有待阐明。这项工作的首要目标是澄清这种独特的放氧反应惊人的催化效率和机理特异性的结构基础。具体目标集中在光谱(主要是共振拉曼，RR)和动力学(冷冻-淬灭)方法，以确定从芳香十氯单胞菌RCB中催化分解ClO2-的中间产物的原子连接性、结构和电子性质。具体地说，这个拟议的项目旨在：1.进一步阐明远端口袋残基在指导底物结合和氯氧键断裂生成CPD-I中的作用。2.用共振拉曼光谱研究了三氯化铁与过氧乙酸的冷冻猝灭反应中，CPD-I中间体的铁基与末端口袋之间的非键相互作用。3.三氯化铁与底物ClO_2~-反应中第一催化中间体的结构和成键。4.研究了反弹态的结构和电子性质。 与公共健康相关：该项目的目标是建立对生物有机体如何制造我们呼吸的氧气的基本理解。这些知识将为开发专门的氧气输送系统的医疗和材料技术提供基础。它还可用于开发从废水和地下水中去除有毒氯基污染物的系统。

DESCRIPTION (provided by applicant): The heme-containing enzyme commonly known as chlorite dismutase (Cld) catalyzes the unimolecular decomposition of chlorite ion, ClO2-, as illustrated in Scheme 1. The reaction is thought to proceed via formation of compound I (2) through a heme-catalyzed isomerization of O-bound chlorite, FeIIIClO2-, to coordinated peroxyhypochlorite, FeIII-OOCl- (3), followed by an intramolecular redox reaction that releases O2, and Cl-. Recent spectroscopic and kinetic work has led to the suggestion that the catalytic mechanism proceeds through a two-electron oxidized heme intermediate having properties characteristic of compound I (Cpd-I). Its formation is thought to occur with release of the two-electron reduced fragment, hypochlorite, which recombines with the yl-oxygen atom of Cpd-I to yield a peroxyhypochlorite complex. This complex is unstable with respect to release of O2 and Cl-. Reactions that evolve O2 are rare in biology, with that catalyzed by the O2-evolving tetranuclear Mn cluster of PSII being the only other known example. The precise nature of the Cld intermediates and the modulation of their reactivities by the enzyme remain to be elucidated. The overarching goal of this work is to clarify the structural basis for the spectacular catalytic efficiency and mechanistic specificity of this unique O2-evolving reaction. The specific aims focus on spectroscopic (primarily resonance Raman, rR) and kinetic (freeze-quench) approaches to determining atom connectivities, structures and electronic properties of intermediates in the catalytic decomposition of ClO2- by Cld from Dechloromonas aromatica RCB. Specifically, this proposed project aims to: 1. further clarify the roles of distal pocket residues in directing substrate binding and Cl-O bond scission to yield Cpd-I. 2. probe the nonbonded interactions between the ferryl moiety of the Cpd-I intermediate and the distal pocket in the freeze quenched reaction of ferric Cld with peracetic acid by resonance Raman spectroscopy. 3. probe structure and bonding in the first catalytic intermediate in the reaction between ferric Cld and the substrate, ClO2-. 4. investigate the structural and electronic properties of the rebounded state. PUBLIC HEALTH RELEVANCE: The goal of this project is to build a basic understanding of how biological organisms make the oxygen that we breath. This knowledge will provide the foundation for development of medical and materials technologies for specialized oxygen delivery systems. It can also be applied to the development of systems for removing toxic chlorine-based pollutants from waste and ground water.