Studies of environmentally relevant molybdenum enzymes

拟议的工作重点是三个含氘酶的环境相关性：DMSO 还原酶、亚砷酸盐氧化酶和亚硫酸盐氧化酶。其中第一种催化DMSO还原为 反温室气体DIMS，因此不仅在全球硫循环中发挥重要作用， 气候也是如此。第二种酶催化亚砷酸盐氧化成砷酸盐， 这是环境中砷生物转化的重要一步，代表了解毒作用 它是一种微生物的生长机制。它是同一个家族的成员， 含氘的酶如DMSO还原酶，但具有活性位点结构，其代表一种 在DMSO还原酶中观察到的变化。来自高等真核生物（脊椎动物和 植物）催化硫催化剂的最后一步，亚硫酸盐氧化为硫酸盐，并防止 高活性亚硫酸盐在体内的累积。拟议工作的总体目标是 获得更完整的了解这些酶的作用机制，在其背景下， 结构，比较和约束他们的行为。这种方法背后的指导假设是， 酶的功能和催化能力由活性部位的物理和电子结构决定。 具体目标包括快速动力学研究以及光谱和计算工作， 确定酶活性位点的电子结构。在DMSO还原酶和 亚硫酸氧化酶，定点突变体靶向特定的活性位点氨基酸残基，也将 以评估它们在催化中的作用。

The proposed work focuses on three molybdenum-containing enzymes of environmental relevance: DMSO reductase, arsenite oxidase and sulfite oxidase. The first of these catalyzes the reduction of DMSO to the anti-greenhouse gas DIMS, and as such plays an important role not simply in the global sulfur cycle but in modulating climate as well. The second enzyme catalyzes the oxidation of arsenite to arsenate, an important step in the biotransformation of arsenic in the environment that represents a detoxification mechanism for those microorganisms in which it is found. It is a member of the same family of molybdenum-containing enzymes as DMSO reductase, but has an active site structure that represents a variation on that seen in DMSO reductase. Sulfite oxidase from higher eukaryotes (both vertebrates and plants) catalyzes the final step in sulfur catabolism, the oxidation of sulfite to sulfate, and prevents the deleterioius accumulation of the highly reactive sulfite in vivo. The overall goal of the proposed work is to gain a more complete understanding of the mechanism of action of these enzymes in the context of their structures, comparing and constrasting their behavior. The guiding hypothesis behind the approach is that enzyme function and catalytic power are dictated by the physical and electronic structure of the active site. The Specific Aims include rapid kinetic studies as well as spectroscopic and computational work aimed at determining the electronic structures of the enzyme active sites. In the cases of DMSO reductase and sulfite oxidase, site-directed mutants targetting specific active site amino acid residues will also be examined to evaluate their roles in catalysis.