Low-Coordinate Synthetic Models for Nitrogenase Activity

固氮酶活性的低坐标合成模型

• 批准号: 8075476
• 负责人: PATRICK L HOLLAND
• 金额: $ 30.54万
• 依托单位: UNIVERSITY OF ROCHESTER
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-04-01 至 2014-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8075476
• 关键词: Active Sites; Amaze; Ammonia; Binding; Bioinorganic Chemistry; Biological; Calculi; Carbon monoxide dehydrogenase; Chemicals; Communities; Complex; Coupling; Crystallization; Crystallography; Data; Databases; Electrochemistry; Electron Nuclear Double Resonance; Electron Transport; Electrons; Environment; Enzymes; Funding; Goals; Hydrazine; Hydrogenase; Iron; Kinetics; Knowledge; Lead; Learning; Life; Ligands; Link; Modeling; Molybdenum; Mononuclear; Nitrogen; Nitrogen Fixation; Nitrogenase; Nuclear; Organic solvent product; Oxidation-Reduction; Pathway interactions; Process; Property; Proteins; Reaction; Research; Roentgen Rays; Role; Scientist; Site; Solid; Solubility; Specific qualifier value; Spectrum Analysis; Structure; Sulfides; Sulfur; Support Groups; Work; absorption; adduct; analog; base; biological systems; biotin synthase; catalyst; chemical reaction; chemical synthesis; cold temperature; diazene; electron nuclear double resonance spectroscopy; fascinate; functional group; functional mimics; insight; novel; oxidation; planetary Atmosphere; public health relevance; small molecule

DESCRIPTION (provided by applicant): Nitrogenases are vitally important enzymes that perform an amazing chemical reaction, the reduction of N2 to ammonia. In nitrogenases, iron-sulfur clusters catalyze multielectron reductions of small molecules, a role that differs from the more common role of iron-sulfur clusters as electron-transfer sites that avoid bond-making and bond-breaking reactions. Little is known about the mechanism of substrate reduction by nitrogenases. Our guiding hypothesis is that nitrogenases and other reactive iron-sulfur cluster enzymes generate a transient open site on an iron atom for substrate binding. Recent spectroscopic work on iron- molybdenum nitrogenase strongly suggests that the mechanism involves binding of N2 to iron, and involves iron-hydride species. However, there are no chemical precedents for iron-sulfur clusters that have an open site, or for iron-sulfur clusters with a hydride. Examples of N2 binding to high-spin iron are rare and understudied. Synthetic compounds with these features are needed to evaluate the feasibility of the proposed functional groups on iron-sulfur clusters, to establish the spectroscopic signatures of these functional groups, and to learn whether their reactivity is consistent with the enzymatic products. In the proposed research, we will create synthetic iron-containing compounds with each of these functionalities: unsaturated iron-sulfur clusters, iron-sulfide-hydride clusters, and iron-N2 complexes. The isolation and characterization of these compounds is made possible by the use of very bulky supporting groups. The bulky groups also facilitate crystallization, and enhance solubility in organic solvents that can be used at low temperature. Crystallography, kinetic studies, electrochemistry, and reactivity will be used to elucidate the atomic-level detail of the elementary steps of small-molecule binding and reduction. The synthetic complexes will be evaluated by ENDOR, infrared, Raman, M"ssbauer, and X- ray absorption spectroscopies to provide a link between the structures of novel model compounds and the known data for nitrogenases. We anticipate that the proposed work will lead to the first solid precedents for reaction pathways in nitrogenases. Although much is known about the mechanisms of multielectron oxidation reactions in bioinorganic chemistry, the knowledge about multielectron biological reductions is much less. Therefore, there is fundamental importance in learning how the iron-sulfide cluster in nitrogenase binds and transforms small molecules that are essential for life. In the long run, understanding the mechanisms of small-molecule reduction in biological systems may also lead to new catalysts for use in chemical synthesis. PUBLIC HEALTH RELEVANCE: Enzymes that contain iron and sulfur produce many of the molecules that are essential for life, but are not understood well. The iron-sulfur enzyme nitrogenase converts unreactive nitrogen in the atmosphere into forms that can be used, and life as we know it is dependent upon this process of "nitrogen fixation." However, the scientific community does not yet know how nitrogenase works. This project aims to show the principles underlying the mechanism of nitrogen fixation, which may also lead to new catalysts for transforming organic and inorganic molecules.

描述（由申请人提供）： 固氮酶是极其重要的酶，可以执行令人惊奇的化学反应，将氮气还原为氨。在固氮酶中，铁硫簇催化小分子的多电子还原，这一作用不同于铁硫簇作为避免成键和断键反应的电子转移位点的更常见作用。关于固氮酶还原底物的机制知之甚少。我们的指导性假设是固氮酶和其他反应性铁硫簇酶在铁原子上产生用于底物结合的瞬时开放位点。最近对铁-钼固氮酶的光谱研究强烈表明，该机制涉及 N2 与铁的结合，并涉及氢化铁物质。然而，对于具有开放位点的铁硫簇，或具有氢化物的铁硫簇，还没有化学先例。 N2 与高自旋铁结合的例子很少见，而且尚未得到充分研究。需要具有这些特征的合成化合物来评估铁硫簇上所提出的官能团的可行性，建立这些官能团的光谱特征，并了解它们的反应性是否与酶产物一致。在拟议的研究中，我们将创建具有以下功能的合成含铁化合物：不饱和铁硫簇、铁硫化物氢化物簇和铁氮络合物。通过使用非常大的支持基团，可以对这些化合物进行分离和表征。大基团还促进结晶，并增强在可在低温下使用的有机溶剂中的溶解度。晶体学、动力学研究、电化学和反应性将用于阐明小分子结合和还原基本步骤的原子级细节。合成复合物将通过 ENDOR、红外、拉曼、M'ssbauer 和 X 射线吸收光谱进行评估，以提供新型模型化合物的结构与固氮酶的已知数据之间的联系。我们预计拟议的工作将导致尽管人们对生物无机化学中多电子氧化反应的机制了解很多，但对多电子生物还原的了解却少得多。从长远来看，了解生物系统中小分子还原的机制也可能会带来用于化学合成的新催化剂。 公共健康相关性：含有铁和硫的酶会产生许多生命必需的分子，但人们对它们的了解还不够深入。铁硫固氮酶将大气中不活泼的氮转化为可用的形式，而我们所知的生命依赖于这种“固氮”过程。然而，科学界尚不清楚固氮酶如何发挥作用。该项目旨在揭示固氮机制的基本原理，这也可能导致用于转化有机和无机分子的新催化剂。