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

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。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SO的晶体学和EXAFS研究中得到的Mo活性中心的一致结构是由轴向氧供体和烯-1，2-二硫醇盐、Cys硫醇盐和赤道平面上的第二氧供体组成的五配位Mo位点。虽然亚硫酸盐孤对攻击面对底物进入通道的赤道氧代的机制是直接的，但硫醇盐和烯-1，2-二硫醇盐配体在促进该反应中的作用尚不清楚。所提出的XAS研究将利用新的混合硫醇盐/硒化盐模型来评估硫醇盐和烯-1，2-二硫醇盐对Mo中心的共价贡献。这些实验的结果将被用来与正在进行的电子吸收，MCD，共振拉曼，EPR和DFT的研究在我们的实验室，以确定SO活性位点的电子结构，以及如何电子结构促进SO催化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.