Co(II)-Radical Pair Dynamics in B12 Enzyme Catalysis

利用缺电子自由基物种的极端反应性的酶进行一些 最困难的化学反应这些酶的区域和立体选择性 打破了长期以来认为激进反应是非特异性的观点。本课程包括以下内容： 核糖核苷酸还原酶，催化DNA生物合成的第一个独特步骤，前列腺素H- 合成酶，阿司匹林和其他非甾体抗炎药的靶点，以及辅酶家族 B12依赖酶，催化代谢产物共价键重排。普通小学 催化剂中的步骤是金属辅助产生缺电子有机自由基。此启动器 自由基本身或通过二级自由基物质促进氢原子从氢原子中的提取。 底物形成基于底物的自由基，打开新的反应通道，促进重排， 一个乘积基一个突出的问题是自由基对如何稳定以防止快速重组， 实现高产率的生产性反应。阐明蛋白质和辅因子如何引导 自由基稳定化和随之而来的底物自由基重排将是持续的重点， 问题研究腺苷钴胺素依赖性系统，特别是乙醇胺脱氨酶， 被选中进行审查。对全酶的组装、自由基对的产生、分离和 稳定化将通过脉冲电子顺磁共振和可见/近红外技术进行研究。 利用低温捕获样品和时间分辨时标跟踪的红外吸收光谱学 范围从皮秒到数小时。研究结果将用于构建详细的分子机制 进行酶反应。这些见解和新方法的发展将促进激进分子的识别 在其他酶反应中的中间体，表明程序化的位点特异性自由基反应的设计， 体内，并协助治疗努力，以打击生物破坏性的自由基。

Enzymes that harness the extreme reactivity of electron-deficient free radical species carry out some of the most difficult chemical reactions in biology. 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-infiamatory drugs, and the family of coenzyme B12-dependent enzymes, which catalyze metabolite covalent bond rearrangements. The common primary step in the catalyses is metal-assisted generation of an electron-deficient organic radical. This initiator radical, either by itself or through secondary radical species, promotes hydrogen atom abstraction from the substrate to form a substrate-based radical, opening a new reaction channel that facilitates rearrangement to a product radical. An outstanding issue is how the radical pair is stabilized against rapid recombination to achieve productive reaction in high yield. 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. The mechanisms of holoenzyme assembly, and radical pair generation, separation and stabilization will be studied by techniques of pulsed-electron paramagnetic resonance and visible/near- infrared absorption spectroscopy by using cryotrapped samples and time-resolved tracking on time scales ranging from picoseconds to hours. The results will be used to construct a detailed molecular mechanism for the enzyme reactions. The insights and novel methods developed will promote identification of radical intermediates in other enzyme reactions, indicate designs for programmed site-specific radical reactions in vivo, and assist therapeutic efforts to combat biologically-destructive free radicals.