MODELS OF NITRATE REDUCTASES AND RELATED ENZYMES

描述：（改编自申请人的摘要）钼是一种必不可少的 所有生命形式所需的微量元素。在人类中， 辅酶直接参与嘌呤代谢（黄嘌呤氧化酶， XO）和硫代谢（亚硫酸盐氧化酶，SO）。钼中的缺陷 辅因子的合成，这两种酶的催化位点，是致命的， 孩子在氮循环中，一种含蝶呤的固氮酶， 还原酶（NR）催化硝酸盐还原为亚硝酸盐。过量的硝酸盐 水污染会严重影响大量人口的健康， 生理紊乱，包括过早终止妊娠。最近， 过量的硝酸盐与非霍奇金淋巴瘤有关。该提案寻求 以模拟NR的某些方面。NR被认为是直接催化氧原子 在一个实施方案中，该方法包括在底物和水分子之间的OAT转移反应。理论 对OAT反应的研究提出了反应途径的建议， 通过一个稳定的中间体，这需要验证， 实验基于蛋白质结构，涉及单氧-Mo（VI）的OAT反应 和desoxo-Mo（IV）中心已被提出用于酶，如异化酶， NR和二甲基亚砜还原酶。为了充分理解这种新颖的反应性， 理解这些中心的电子结构是至关重要的。的 结构研究也明确表明，钼中心，这是 催化位点都埋在蛋白质骨架里树突状 分子已被用于模拟金属蛋白，如血红素和铁硫 proteins.本研究的总体目标是了解 NR通过无机，物理和理论研究的综合计划， 合成分子研究人员将使用离散的定义明确的小 分子来回答详细的问题，如几何的建议， 中间体，并合成大的树枝状分子，以接近建模 蛋白质的结构特征，如包封。这些化合物将 结合电化学、光学、化学和生物化学等技术 光谱学和磁共振光谱学。的具体目标 建议如下： 1.为了理解氧原子转移反应的机理， 离散钼配合物，并探讨电子的细节 钼（VI，IV）中心的结构。 2.开发树突状系统，用于评估蛋白质 对钼中心性质的影响。 研究人员认为，用结果回答这些关键问题 建议的研究将提供一个更好的了解NR和其他 含蝶呤的腺苷酸酶以及一般的金属酶。

DESCRIPTION: (adapted from applicant's abstract) Molybdenum is an essential trace element required for all forms of life. In humans pterin-containing molybdoenzymes are directly involved in purine metabolism (xanthine oxidase, XO), and in sulfur metabolism (sulfite oxidase, SO). Defects in the 'molybdenum cofactor' synthesis, the catalytic site of these two enzymes, are fatal in children. In the nitrogen cycle, a pterin-containing molybdoenzyme, nitrate reductase (NR), catalyzes the reduction of nitrate to nitrite. Excess nitrate in water affects the health of a significant population by causing severe physiological disorders including premature termination of pregnancy. Recently, excess nitrate has been linked with non-Hodgkin's lymphoma. This proposal seeks to model certain aspects of NR. NRs are thought to catalyze direct oxygen atom transfer (OAT) reaction between a substrate and a water molecule. Theoretical studies of the OAT reaction has led to a proposal for the reaction pathway, that passes through a stable intermediate, which needs to be validated by experiment. Based on protein structures, OAT reactions involving monooxo-Mo(VI) and desoxo-Mo(IV) centers have been proposed for enzymes such as dissimilatory NR and dimethylsulfoxide reductase. To fully understand this novel reactivity, it is critical to understand the electronic structures of such centers. The structural studies also unequivocally showed that Mo-centers, which are the sites of catalysis, are buried inside the protein scaffolding. Dendritic molecules have been used to model metalloproteins such as heme and iron-sulfur proteins. The overall goal of this research is to understand the reactivity of NR by an integrated program of inorganic, physical and theoretical studies on synthetic molecules. The investigators will use discrete well-defined small molecules for answering detailed questions such as the geometry of the proposed intermediate, and synthesize large dendritic molecules to approach modeling the protein architectural features such as encapsulation. These compounds will be analyzed with a combination of techniques such as electrochemistry, optical spectroscopy, and magnetic resonance spectroscopy. The specific aims of the proposal are: 1. To understand the mechanism of the oxygen atom transfer reaction with discrete molybdenum complexes and to explore the details of the electronic structure of molybdenum (VI,IV) centers. 2. To develop dendritic systems for evaluating the effect of protein scaffolding on the properties of molybdenum centers. The investigators believe that answering these critical questions with results of the proposed research will provide a better understanding of NR and other pterin-containing molybdoenzymes as well as metalloenzymes in general.