Low-Coordinate Synthetic Models for Nitrogenase Activity

固氮酶活性的低坐标合成模型

• 批准号: 7390716
• 负责人: PATRICK L HOLLAND
• 金额: $ 18.82万
• 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 2010-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7390716
• 关键词: Address; Affect; Amaze; Ammonia; Anabolism; Bacterial Transformation; Binding; Biochemistry; Characteristics; Chemistry; Class; Classification; Cleaved cell; Complex; Decompression Sickness; Electron Transport; Electronics; Electrons; Enzymes; Evaluation; Goals; Hydrogen; Ions; Iron; Iron Compounds; Kinetics; Lead; Learning; Ligands; Literature; Location; Metals; Methods; Modeling; Molybdenum; Molybdoferredoxin; Mutation; Nitrogen; Nitrogenase; Numbers; Object Attachment; Organic Iron Compounds; Oxidation-Reduction; Pattern; Plants; Process; Property; Protein Binding; Proteins; Protons; Rate; Reaction; Site; Substrate Specificity; Work; base; catalyst; protonation; research study; sample fixation; trend

Bacterial nitrogenases catalyze the reduction ("fixation") of N/2 to ammonia, an amazing process that gives the precursor to all nitrogen-containing biomolecules. Because it is the ultimate multielectron reduction, discovery of the detailed mechanism of nitrogenase is a great challenge in biochemistry. N2 reduction occurs at a metal cluster called the FeMoco. After addition of electrons and protons, the FeMoco somehow binds, breaks, and protonates N2 to NH4*. Mutations near the FeMoco show that N2 and other substrates bind near the iron-rich center of the cluster. Based on literature crystallographic, spectroscopic, and mechanistic studies on nitrogenase, we have formulated a reasonable iron-based mechanism for reduction and N2 binding. This mechanism, based on low-coordinate iron, serves as our guiding hypothesis. Key intermediates have iron with only 3 or 4 attachments, and others with Fe-H bonds. However, the literature has few synthetic 3-coordinate iron compounds, and no Fe-H complexes with a coordination number of four or less. This proposal describes the systematic study of synthetic low-coordinate iron compounds: their properties, spectroscopic signatures, reactivity toward nitrogenase substrates, and characteristic reaction patterns. Experiments are chosen to address several steps of the hypothetical mechanism, including reductive activation, N2 binding, N2 reactions and cleavage, and N-H bond formation. Because isolated Fe-H complexes completely break multiple bonds, they will be studied as reactivity models for nitrogenase intermediates. Multimetallic complexes with constrained geometry will show the arrangement most conducive to N2 cleavage. Mechanistic studies on key reactions will clarify allowed and forbidden reactions of iron atoms like those in the hypotheticaL FeMoco mechanism. These studies will elucidate the fundamentals of low-coordinate iron chemistry, which is necessary to understand the workings of the FeMoco and large synthetic clusters.

细菌固氮酶催化 N/2 还原（“固定”）为氨，这是一种令人惊奇的现象 产生所有含氮生物分子的前体的过程。由于它是最终的多电子还原，固氮酶详细机制的发现是生物化学中的巨大挑战。 N2 还原发生在称为 FeMoco 的金属簇上。添加电子和质子后，FeMoco 以某种方式结合、断裂 N2 并将其质子化为 NH4*。 FeMoco 附近的突变表明 N2 和其他底物结合在簇的富铁中心附近。基于固氮酶的文献晶体学、光谱学和机理研究，我们制定了合理的铁基还原和 N2 结合机制。这种基于低配位铁的机制是我们的指导假设。关键中间体中的铁仅具有 3 或 4 个连接，其他中间体则具有 Fe-H 键。然而，文献中很少有合成的3配位铁化合物，也没有配位数为4或更少的Fe-H配合物。 该提案描述了合成低配位铁化合物的系统研究： 它们的特性、光谱特征、固氮酶底物的反应性，以及 特征反应模式。选择实验来解决假设机制的几个步骤，包括还原活化、N2 结合、N2 反应和裂解以及 N-H 键形成。由于分离的 Fe-H 复合物完全破坏了多重键，因此它们将作为固氮酶中间体的反应模型进行研究。具有受限几何形状的多金属配合物将显示出最有利于 N2 裂解的排列。对关键反应的机理研究将阐明铁原子允许和禁止的反应，如假设的 FeMoco 机制中的反应。这些研究将阐明低配位铁化学的基础知识，这对于理解 FeMoco 和大型合成团簇的工作原理是必要的。