XAS STUDIES OF THE THIOLATE LIGAND DONORS IN MODELS OF THE SULFITE OXIDASE ACTIV

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。亚硫酸盐氧化酶(SO)是一种单核钼酶，负责将亚硫酸盐转化为硫酸盐，这是半胱氨酸和蛋氨酸降解的最终步骤。从鸡肝的结晶学和EXAFS研究中得到的钼活性中心的共同结构是由赤道平面上的一个轴向氧供体和一个烯-L，2-二硫代，一个半硫代和第二个氧供体组成的五配位的钼中心。虽然亚硫酸盐对面对底物访问通道的赤道氧原子的单对攻击机制是直接的，但硫代和烯-L，2-二硫代硫代配体在促进这一反应中的作用尚不清楚。建议的XAS研究将利用新的硫酸盐/亚硒酸盐混合模型来评估硫酸盐和烯-L，2-二硫酸盐对Mo中心的共价性贡献。这些实验结果将结合我们实验室正在进行的电子吸收、MCD、共振拉曼、EPR和DFT研究来确定SO活性中心的电子结构，以及该电子结构如何促进SO催化中的氧化和还原半反应。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Sulfite oxidase (SO) is a mononuclear molybdenum enzyme responsible for the conversion of sulfite to sulfate, the terminal step in cysteine and methionine degradation. The consensus structure of the Mo active site derived from both crystallographic and EXAFS studies of the chicken liver SO is that of a five coordinate Mo site consisting of an axial oxo donor and an ene-l,2-dithiolate, a Cys thiolate and a second oxo donor in the equatorial plane. While the mechanism of the sulfite lone-pair attack on the equatorial oxo that is facing the substrate access channel is straight-forward, the role of the thiolate and ene-l,2-dithiolate ligands in facilitating this reaction is unclear. The proposed XAS studies will utilize novel mixed thiolate/selenolate models to assess the covalency contributions of the thiolate and ene-l,2-dithiolate to the Mo center. The results of these experiments will be used in conjunction with ongoing electronic absorption, MCD, resonance Raman, EPR and DFT studies in our laboratory to determine the electronic structure of the SO active site, and how the electronic structure facilitates both the oxidative and reductive half-reactions in SO catalysis.