Models for nitrate reductases and related enzymes

描述（由申请人提供）：钼辅因子（Moco）是一种重要的金属中心，位于多种酶的催化核心。独特而“普遍”的Moco在所有单核钼酶（MMEs）中具有相同的核心结构，并且存在于所有形式的生命中。这种辅助因子介导氧原子转移（OAT）和羟基化反应的能力导致了MMEs家族的多样化。类似的MMEs包括脱氢酶（如甲酸、乙苯）、氧化酶（如硫化物、黄嘌呤、亚砷酸盐）和还原酶（如硝酸盐、砷酸盐、硒酸盐）。在人体中，黄嘌呤氧化酶和亚硫酸盐氧化酶在硫和嘌呤代谢的氧化还原反应中起着至关重要的作用。微生物微生态系统还通过转化硝酸盐和砷间接影响人类健康。辅因子合成缺陷可导致严重的生理异常导致死亡。生物学和医学中的一个基本问题是Moco的基本单位是如何被调整来实现各种功能的。我们研究的最终目标是通过无机、有机、物理和反应性研究的综合项目，更好地了解微微微粒的反应性。我们感兴趣的主要问题是：是什么控制了微型微型企业的反应性？物理结构如何施加电子结构以支持不同活性位点的相同底物转变？这些活性位点如何影响催化循环的不同阶段，即底物结合、产物形成、产物释放和活性位点的再生？这些问题将通过研究钼配合物的OAT反应性和氧化还原性质以及检查辅助因子的各个组分施加的影响来解决。我们还将合成二硫酮配体的氧钼配合物并对其进行全面表征，并研究其性质。此外，我们还进行了从铜到钼的金属转化反应，并完成了最接近的吡蝶呤辅因子的合成。按照R15计划的指导方针，我们将继续培养下一代科学家。本提案旨在通过假设驱动的研究，解决与一类对人类健康重要的酶有关的基本问题。

DESCRIPTION (provided by applicant): The molybdenum cofactor (Moco) is a remarkable metal center that lies at the catalytic heart of a variety of enzymes. The unique and `universal' Moco has the same core structure in all mononuclear molybdenum enzymes (MMEs) and is found in all forms of life. The ability of this cofactor to mediate oxygen atom transfer (OAT) and hydroxylation reactions, has given rise to the diverse family of MMEs. Similarly constituted, MMEs include dehydrogenases (e.g., formate, ethylbenzene), oxidases (e.g., sulfide, xanthine, arsenite), and reductases (e.g., nitrate, arsenate, selenate). In humans, xanthine oxidase and sulfite oxidase fulfill crucial functions in redox reactions in sulfur and purine metabolism. Microbial MMEs also indirectly impact human health through transformation of nitrate and arsenic. Defects in cofactor synthesis can result in severe physiological abnormalities leading to death. A fundamental question in biology and medicine is how has the basic unit of Moco been tuned to fulfill the various functions. The ultimate goal of our research is to better understand the reactivity of MMEs through an integrated program of inorganic, organic, physical, and reactivity studies. The broad questions that we are interested in answering are: What controls the reactivity in MMEs? How does the physical structure impose electronic structures that support the same substrate transformation with different active sites? How do these active sites influence the different phases of the catalytic cycle i.e., substrate binding, product formation, product releases and regeneration of the active site? These questions will be addressed by investigating the OAT reactivity and redox properties of molybdenum complexes and examining influence imposed by individual components of the cofactor. We will also synthesize and fully characterize oxo molybdenum complexes of dithione ligands, and investigate their properties. In addition, we conduct transmetallation reaction from copper to molybdenum, and complete the synthesis of the closest analog of pyranopterin cofactor. In accordance with the guideline of R15 program we will continue to train next generation of scientists. This proposal seeks to address fundamental questions relating to a class of enzymes that are important to human health though a hypothesis driven research.