MODEL STUDIES OF ACETYL COENZYME A SYNTHASE

所提出的研究被设计为使用明确定义的低分子量系统来阐明由含镍乙酰辅酶A合酶（ACS）催化的基本步骤的机理参数。 这些步骤中包括非酶促的甲基从类咕啉蛋白（C/Fe-SP）转移到A簇，CO插入到CH 3-A簇键和硫醇加成到CH 3C（O）-A簇。 为此，首先有必要制备含有催化位点（A簇）的关键特征的合成类似物。与所有光谱数据一致的结构模型（X射线结构不可用）包括在（N/O）2S 2供体环境中通过共价桥X连接到[Fe 3S 4]2+簇的单个镍离子。 化学反应性研究将需要使用合成类似物探测化学计量转换。 个别反应将使用机械无机化学的协议，包括产品分析，动力学测量，立体化学和自由基时钟探针调查系统地询问。 这个项目的长期目标是发展一个详细的机制理解如何优化生物异金属簇的结构，电子和化学性质的预期催化转化。拟议的研究影响了我们对必需微量元素镍的生物学意义的理解，包括与消化性溃疡疾病，胃癌和胃淋巴瘤相关的幽门螺杆菌的男性能力，以及通过产生降解DNA的氧化物质的致癌作用。 此外，产丙酮和产甲烷细菌，含有ACS的生物体，可能对人类消化功能和功能障碍很重要，因为它们占据了结肠的大体积。 更广泛地说，更深入地了解ACS是有价值的，我们的基本理解的一般类的生物异金属组件，例如，在[NiFe]氢化酶，亚硫酸盐还原酶，细胞色素c氧化酶，[CuZn]超氧化物歧化酶和固氮酶辅因子的催化位点。

The proposed research is designed to elucidate the mechanistic parameters of the elementary steps catalyzed by the nickel- containing acetyl-coenzyme A synthase (ACS) using well-defined low molecular weight systems. Included among these steps are the nonenzymatic transfer of a methyl group from the corrinoid protein (C/Fe-SP) to the A cluster, CO insertion into the CH3-A cluster bond and thiolate addition to the CH3C(O)-A cluster. To this end, first it will be necessary to prepare synthetic analogs that contain the key features of the catalytic site (A cluster). A structural model consistent with all spectroscopic data (an X- ray structure is not available) includes a single nickel ion in a (N/O)2S2 donor environment linked through a covalent bridge, X, to an [Fe3S4]2+ cluster. Chemical reactivity studies will entail probing stoichiometric transformations using the synthetic analogs. Individual reactions will be systematically interrogated using the protocols of mechanistic inorganic chemistry including product analyses, kinetic measurements, stereochemical and radical clock probe investigations. The long- term goal of this project is to develop a detailed mechanistic understanding of how the structural, electronic and chemical properties of biological heterometallic clusters are optimized for the intended catalytic transformations. The proposed research impacts our understanding of the biological implications of the essential trace element nickel that include the virility of Helicobacter pylori which has been associated with peptic ulcer disease, gastric carcinoma, and gastric lymphoma, and carcinogenesis through production of oxidizing species that degrade DNA. Additionally, acetongenic and methanogenic bacteria, organisms that contain ACS, may be important to human digestive function and dysfunction as they occupy a large volume of the colon. More broadly, a deeper understanding of ACS is valuable to our fundamental understanding of the general class of biological heterometallic assemblies, e.g. the catalytic sites in [NiFe] hydrogenase, sulfite reductase, cytochrome c oxidase, [CuZn] superoxide dismutase and the nitrogenase cofactor.