Studies of environmentally relevant molybdenum enzymes

拟议的工作重点是与环境有关的三种含钼酶：DMSO 还原酶、亚砷酸氧化酶和亚硫酸盐氧化酶。其中第一个催化将DMSO还原为 反温室气体变暗，因此不仅在全球硫循环中发挥着重要作用，而且在 也在调节气候。第二种酶催化亚砷酸盐氧化成亚砷酸盐，以及 环境中砷的生物转化的重要一步，代表着一种解毒 对于那些发现它的微生物的机制。它是同一个家族的成员 含钼酶，如DMSO还原酶，但具有活性部位结构，代表 在DMSO还原酶中看到的变异。来自高等真核生物(脊椎动物和 植物)催化硫分解代谢的最后一步，即亚硫酸盐氧化成硫酸盐，并防止 高活性亚硫酸盐在体内的有害生物积累。拟议工作的总体目标是 更全面地了解这些酶的作用机制 结构，比较和约束它们的行为。该方法背后的指导性假设是 酶的功能和催化能力由活性中心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，目的是 测定酶活性部位的电子结构。在DMSO还原酶和 亚硫酸盐氧化酶，针对特定活性部位氨基酸残基的定点突变体也将 检查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.