Mossbauer Studies of Nitrite Reductase and Vanadium-containing Nitrogenase

生命物质是由大规模的循环维持的， 能源和化学元素，以及最重要的 生物材料中的元素是氮。 研究 许多不同的生物过程控制着氮 因此，在生物圈中的地位至关重要。 固氮酶和亚硝酸还原酶是两种酶， 催化氮循环的关键步骤。 固氮酶 催化大气中的二氮转化为氨 （固氮）和许多微生物利用它来 将氮吸收到生命系统中。 硝酸还原酶 将亚硝酸盐还原为氨和多种硝酸盐还原剂， 细菌，以及一些硫酸盐还原菌，使用它 最终呼吸和异化氮回到 物理世界 结构和功能的研究， 因此，酶具有根本的重要性， 提供与了解我们的 生活环境 在本申请中，Huynh博士建议执行 以下酶的穆斯堡尔谱研究： 1. 固氮酶的钒铁蛋白 棕色固氮菌（Azotobacter vinelandii） 2. 脱硫弧菌亚硝酸盐还原酶 脱硫菌 钒铁蛋白和亚硝酸盐还原酶都是 含有多个铁中心的复合酶， 可以 最有效的研究方法是穆斯堡尔光谱学。 的 建议的实验包括（i）表征的 天然酶，（ii）氧化还原滴定研究，（iii）pH- 依赖性调查和（iv）检查基质- 和配体结合效应。 穆斯堡尔谱的结果将是 与从其他物理-生物化学 方法，包括光学和电子顺磁共振 技术. Huynh博士希望能够完全描述铁的特性 在这些酶的中心，以获得物理和生化 性质，以揭示这些铁中心发挥的作用， 它们的酶功能，并提高我们对 生物固氮与亚硝酸盐的机理 还原

Living matters are sustained by large-scale cycles of energy and chemical elements, and one of the most essential elements in biological materials is nitrogen. To study the many different biological processes which govern the nitrogen status in the biosphere is, therefore, of vital importance. Nitrogenase and nitrite reductase are two enzymes which catalyze key steps in the nitrogen cycle. Nitrogenase catalyzes the conversion of atmospheric dinitrogen into ammonia (nitrogen fixation) and many microorganisms use it to assimilate nitrogen into the living system. Nitrate reductase reduces nitrite to ammonia and a variety of nitrate-reducing bacteria, as well as some sulfate reducing bacteria, use it for terminal respiration and dissimilates nitrogen back to the physical world. Structural and functional studies of these enzymes are therefore of fundamental importance and should provide information pertinent to the understanding of our living environment. In this application, Dr. Huynh proposes to perform Mossbauaer studies of the following enzymes: 1. the vanadium-iron protein of the nitrogenase enzyme system from Azotobacter vinelandii. 2. the nitrite reductase from Desulfovibrio desulfuricans. Both the vanadium-iron protein and nitrite reductase are complex enzymes containing multiple iron centers which can be most effectively studied by Mossbauer spectroscopy. The proposed experiments include (i)characterizations of the native enzymes, (ii)redoxtitration studies, (iii) pH- dependence investigations and (iv)examinations of substrate- and ligand-binding effects. The Mossbauer results will be correlated with data obtained form other physico-biochemical methods, including optical and electron paramagnetic resonance techniques. Dr. Huynh hopes to fully characterize the iron centers in these enzymes, to obtain physical and biochemical properties, to reveal the roles these iron centers play in their enzymatic functions and to enhance our understanding of the mechanisms of biological nitrogen fixation and nitrite reduction.