Studies of environmentally relevant molybdenum enzymes

描述(由申请人提供)：建议的工作重点是三种与环境有关的含钼酶：二甲基亚砜还原酶、亚砷酸盐氧化酶和亚硫酸盐氧化酶。第一种是催化将DMSO还原为抗温室气体DIMS，因此不仅在全球硫循环中发挥着重要作用，而且在调节气候方面也发挥着重要作用。第二种酶催化亚砷酸盐氧化成亚砷酸盐，这是环境中砷生物转化的重要步骤，代表了发现砷的微生物的解毒机制。它是与DMSO还原酶相同的含钼酶家族的成员，但其活性部位结构与DMSO还原酶的活性部位结构不同。高等真核生物(脊椎动物和植物)中的亚硫酸盐氧化酶催化硫分解代谢的最后一步，即亚硫酸盐氧化为硫酸盐，并防止体内高活性亚硫酸盐的有害积累。拟议工作的总体目标是在其结构的背景下更完整地了解这些酶的作用机制，比较和对比它们的行为。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旨在确定酶活性部位电子结构的光谱和计算工作。在DMSO还原酶和亚硫酸盐氧化酶的情况下，还将检查针对特定活性部位氨基酸残基的定点突变体，以评估它们在催化中的作用。

DESCRIPTION (provided by applicant): 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 contrasting 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 targeting specific active site amino acid residues will also be examined to evaluate their roles in catalysis.