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

利用缺电子自由基的极端反应性的酶 物种进行一些生物学上最困难的化学反应。的 这些酶实现的区域和立体选择性挑战了长期以来的想法 自由基反应是非特异性的本课程包括以下内容： 核糖核苷酸还原酶，催化DNA中的第一个独特步骤 生物合成，前列腺素H-合成酶，阿司匹林和其他非甾体类药物的靶点 抗炎药，S-腺苷甲硫氨酸依赖性 酶，有超过六百个成员，催化广泛的自由基介导的 氧化还原反应和辅酶B12（腺苷钴胺素）依赖性 酶超家族，其成员催化代谢产物共价键 重新安排在这些化学性质不同的生物中， 催化剂是缺电子有机自由基的金属辅助生成。 该引发剂自由基，或者通过其自身或者通过次级自由基物质， 促进氢原子从衬底上剥离以形成基于衬底的 自由基，打开一个新的反应通道，有利于转化为 该产品.一个突出的问题是激进对如何稳定， 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生成的基本原理， 稳定化、蛋白质内自由基迁移和自由基重排将被 持续关注拟议的研究。辅酶B12依赖性 酶，特别是乙醇胺氨裂解酶，已经被选择用于 审查分子结构和动力学对酶的贡献 将使用脉冲电子顺磁技术研究函数 共振和可见/近红外吸收光谱，在低温阱 以及时间分辨系统，其时间范围从皮秒到小时。 基本的见解和新的方法开发将促进 其他生物活性物质自由基中间体的鉴定和表征 反应，告知程序化自由基反应性的设计，并协助 对抗有害的自由基过程的分子治疗努力。

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 nonsteroidal anti-inflammatory drugs, the S-adenosylmethionine-dependent enzymes, with over six-hundred members that catalyze a wide range of radicalmediated redox reactions, and the coenzyme B12 (adenosylcobalamin)-dependent enzyme superfamily, whose members catalyze metabolite covalent bond rearrangements. The common primary step in these chemically-disparate 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 substratebased radical, opening a new reaction channel that facilitates transformation to the product. 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 cofactor guide radical generation, stabilization, intra-protein radical migration, and radical rearrangement will be sustained focuses of the proposed studies. The coenzyem B12-dependent enzymes, and ethanolamine ammonia-lyase specifically, have been selected for scrutiny. The contributions of molecular structure and dynamics to enzyme function will be studied by using techniques of pulsed-electron paramagnetic resonance and visible/near-infrared absorption spectroscopy, in cryotrapped and time-resolved systems on time scales ranging from picoseconds to hours. The fundamental insights and novel methods developed will promote identification and characterization of radical intermediates in other biological reactions, inform the design of programmed radical reactivity, and assist molecular-therapeutic efforts to combat pernicious free radical processes.