COBALT(II)-RADICAL PAIR DYNAMICS IN B12 ENZYME CATALYSIS

B12 酶催化中的钴 (II)-自由基对动力学

• 批准号: 2703673
• 负责人: KURT WARNCKE
• 金额: $ 13.25万
• 依托单位: EMORY UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-03-15 至 2002-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/2703673
• 关键词: cobalamin; cobalt; electron spin resonance spectroscopy; enzyme mechanism; enzyme structure; enzyme substrate; vitamin B12 coenzyme; cobalamin; cobalt; electron spin resonance spectroscopy; enzyme mechanism; enzyme structure; enzyme substrate; vitamin B12 coenzyme

An emergent class of enzymes that harness the extreme reactivity of electron-deficient free radical species to carry out some of the most difficult chemical reactions in biology has been recently identified. The regio- and stereo-selectivity achieved by these enzymes defies long- held ideas that radical reactions are non-specific. This class includes the following: ribonucleotide reductases, which catalyze the first unique step in DNA biosynthesis, prostaglandin H-synthase, the target of aspirin and other non-steroidal anti-inflammatory drugs, and the family of B12 coenzyme-dependent enzymes, which catalyze metabolite covalent bond rearrangements. The common primary step in the catalysis is metallocenter- or metal-assisted generation of an electron-deficient organic radical. This initiator radical abstracts a hydrogen atom from the substrate to form a substrate-based radical, opening a new reaction channel that facilitates rearrangement to a product radical. A challenging issue is how the radical is stabilized against recombination with the metal. There are analogies with the charge separation reactions in photosynthetic and respiratory bioenergetic complexes, for which the rudimentary performance principles have been established. However, unlike simple electron-hole separation by electron tunneling among weakly interacting redox sites, metal-radical separations involve large- scale movement of heavy nuclei and relatively strong electronic interactions. Elucidating the basic principles of how protein and cofactors guide radical stabilization and ensuing substrate radical rearrangement will be sustained focuses of the proposed studies. The adenosylcobalamin-dependent systems, and ethanolamine deaminase specifically, have been selected for scrutiny because homolytic cleavage of the cobalt-carbon bond to form the CoII metalloradical and 5'- adenosyl initiator radical can be triggered by a visible laser pulse, allowing the coherent preparation of the radical pair state under catalytic conditions. The radical pair separation and substrate radical rearrangement will be tracked by time-resolved techniques of pulsed-EPR spectroscopy. Dynamic electron spin-spin and electron-nuclear hyperfine interactions will be measured and used to construct a detailed molecular mechanism. The insights and techniques developed will promote identification of transient radical intermediates in other enzyme reactions, indicate designs for programmed site-specific radicals reactions in vivo, and assist therapeutic efforts to combat biologically-destructive free radicals.

一系列新兴的酶，利用了极端反应性 电子缺陷的自由基物种，以执行最多的自由基 最近已经确定了生物学中的难以化学反应。 这些酶实现的区域和立体式选择性持续很长 持有激进反应是非特异性的想法。 此课程包括 以下：核糖核苷酸还原酶，催化第一个 DNA生物合成的独特步骤，前列腺素H合酶，靶标 阿司匹林和其他非甾体类抗炎药，以及 B12辅酶依赖性酶的家族，该酶催化代谢物 共价键重排。 催化的常见主要步骤 是金属中心或金属辅助的电子缺陷的生成 有机自由基。 该引发剂自由基摘要从 形成基于底物的激进的底物，打开新反应 通道促进重新排列到产物自由基。 一个 具有挑战性的问题是如何对重组进行激进 用金属。与电荷分离反应有类比 在光合和呼吸生物能络合物中 已经建立了基本的绩效原则。然而， 与简单的电子孔通过电子隧道分离而不同 弱相互作用的氧化还原部位，金属 - 激进的分离涉及大的 重核和相对强的电子的比例运动 互动。 阐明蛋白质和如何 辅助因子指导自由基稳定和随后的底物自由基 拟议研究将持续重新排列。 这 腺苷蛋白依赖性系统和乙醇胺脱氨酶 具体而言，由于同型裂解而被选择进行审查 钴 - 碳键形成COII金属形和5'- 可以通过可见的激光脉冲触发腺苷引发剂自由基， 允许从 催化条件。 自由基对分离和底物自由基 重排将通过脉冲 - epr的时间分辨技术跟踪 光谱法。动态电子自旋和电子核超精 相互作用将被测量并用于构建详细的分子 机制。 开发的见解和技术将促进 在其他酶中鉴定瞬态自由基中间体 反应，指示编程特定地点的自由基的设计 体内反应，并协助治疗努力 生物损害的自由基。