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 物种执行生物学中一些最困难的化学反应。这个 这些酶实现的区域和立体选择性打破了长期以来的观点 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中独特的第一步 生物合成、前列腺素H合成酶、阿司匹林和其他非类固醇的靶标 抗炎药物对S-腺苷蛋氨酸的依赖 酶，有600多个成员，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)依赖 酶超家族，其成员催化代谢物共价键 重新安排。在这些化学上完全不同的 催化剂是一种金属辅助生成的缺电子有机自由基。 该引发剂自由基本身或通过次级自由基物种， 促进从底物中提取氢原子，形成以底物为基础的 自由基，打开一个新的反应通道，促进转化为 产品。一个悬而未决的问题是如何稳定激进分子对 快速复合，实现高产率的高效反应。澄清 蛋白质和辅因子如何引导自由基产生的基本原理， 稳定、蛋白质内自由基迁移和自由基重排将是 拟议研究的持续重点。辅酶B12依赖基因 酶，特别是乙醇胺解氨酶，已被选为 仔细检查。分子结构和动力学对酶的贡献 将利用脉冲电子顺磁技术来研究功能 低温陷阱中的共振和可见光/近红外吸收光谱 以及时间尺度从皮秒到几小时的时间分辨系统。 开发的基本见解和新方法将促进 其他生物中自由基中间体的鉴定和表征 反应，通知程序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.