MECHANISTIC METALLOBIOCHEMISTRY OF COENZYME B12

这项研究的广泛和长期目标是提供一个 腺苷钴胺素（辅酶）家族的分子水平的理解 催化C-H键活化的B 12）依赖性和相关酶， 随后发生重排或还原反应。该系列 酶包括具有B 12、Fe 2、Mn 2的酶（可能还有其他酶， 发现的）活动场所。最近的证据表明，这些酶使用 一个不寻常的，仍然知之甚少，激进的连锁作用机制; 这些酶在细菌、植物和哺乳动物中的广泛分布 包括人类在内的所有生物都证明了这种自由基链机制的重要性。 辅酶B12辅因子是正常成熟所必需的， 红细胞;在男人，不足B12导致恶性贫血， 包括巨幼细胞性贫血，恶性肿瘤， 和神经系统疾病。更具体地说，腺苷钴胺素是一种 甲基丙二酰辅酶A β和甲钴胺的必要辅因子是一种 同型半胱氨酸甲基转移酶的必需辅因子。 所概述的具体目标旨在提供一个化学范例， 被认为是操作过程中的单个的、基本的机械步骤， 辅酶B12引发的自由基链反应。此外， 步骤，辅酶B12的Co-C键的初始均裂，经历一个 异常大，1012，酶速率增强。理解这一 巨大的影响，在这个也许是原型系统，是另一个焦点， 这些研究。最后，研究概述，涉及一个中央辅酶 B12具有一个或两个共价连接的多肽α-螺旋。这项工作， 其利用了B12辅因子的接近理想的特征， 开始探讨一个非常重要和普遍但又不太清楚的问题 多肽和蛋白质的低频运动如何与酶结合 催化反应坐标，如简单（因此接近理想） Co-C裂解反应坐标。这种蛋白质辅助动力学是 维持生命的酶转化的基本成分 生物，但仍然知之甚少。

The broad and long-term objectives of this research are to provide a molecular level understanding of the family of adenosylcobalamin (Coenzyme B 12)-dependent and related enzymes that catalyze C-H bond activations, followed by rearrangement or reduction reactions, in nature. This family of enzymes includes those with B 12, Fe2, Mn2 (and probably other, yet to be discovered) active sites. Recent evidence suggests that these enzymes use an unusual, and still poorly understood, radical chain mechanism of action; the wide distribution of these enzymes in bacteria, plants, and mammals including humans attests to the importance of this radical chain mechanism. The Coenzyme B12 cofactor is essential for the normal maturation of erythrocytes; in man, insufficient B12 leads to pernicious anemia and clinical features that include megaloblastic anemia, malignant neoplasms, and neurological disorders. More specifically, adenosylcobalamin is an essential cofactor for methylmalonyl-CoA mutase and methylcobalamin is an essential cofactor for homocysteine methyltransferase. The specific aims outlined are designed to provide a chemical paradigm for the individual, elementary mechanistic steps thought to operate in the Coenzyme B12-initiated radical chain reaction. Furthermore, one of the steps, the initial homolysis of Coenzyme B12's Co-C bond, is subject to an unusually large, 1012, enzymic rate enhancement. Understanding this enormous effect, in this perhaps prototype system, is another focus of these studies. Lastly, studies are outlined that involve a central Coenzyme B12 With one or two covalently linked polypeptide a-helices. This work, which takes advantage of the nearly ideal features of the B12 cofactor, begins to probe the very important and general but ill-understood question of how polypeptide and protein low frequency motions couple to an enzyme catalysis reaction coordinate, such as the simple (and thus nearly ideal) Co---C cleavage reaction coordinate. Such protein-assisted dynamics are essential components of the enzymic transformations that sustain living organisms, yet remain poorly understood.