The Hydroxylamine Oxidizing System of Nitrosomonas

在土壤中，化肥氨被化学自养硝化细菌亚硝化单胞菌氧化成亚硝酸盐（NH3 + 1.5 O2-HNO 2 + H2）。亚硝酸盐被硝化菌氧化成硝酸盐，硝酸盐是非豆科作物中食物蛋白质的主要氮源。 亚硝化单胞菌是大多数食物氮的重要经济转化菌。 具有重要经济意义的是土壤中的N作为NH3氧化过程中由亚硝化单胞菌产生的N-气体或通过硝化细菌还原硝酸盐而损失。 通过反硝化作用控制农业损失的尝试是使用亚硝化单胞菌属的氨氧化抑制剂。 这对提高氨氧化机理的认识具有重要意义。 NH3被O2氧化成NH 2 OH，然后被羟胺氧化还原酶“HAO”氧化（NH 2 OH + H2O-HNO 2 + 4 e-+4H+）。 HAO是一种大而异常复杂的血红素蛋白（7个c-血红素和1个底物结合。 “P460”组/63 kDa蛋白）。 四个电子从HAO传递到四血红素细胞色素c-554。 两个电子从细胞色素c-554以单独的电子转移链传递到氨氧化反应。 另外两个电子传递到膜末端氧化酶、异化亚硝酸盐还原酶（在低氧生长期间）、ATP依赖性NAD还原酶或过氧化物酶（以清除过氧化物）。 该项目的目标是HAo酶的分析。 我们打算确定HAO结构的细节，特别注意活性位点和周转机制。 该方法涉及光谱学，肽分析，动力学，自杀底物，电子顺磁共振光谱，穆斯堡尔谱和X射线晶体学分析。 土壤和水细菌亚硝化单胞菌对自然界中的氮循环、温室气体和臭氧破坏气体的产生、农业中的氮可用性以及氯化污染物的降解至关重要。 该项目涉及研究生物催化剂的结构，使生物体能够发挥这些作用。 这种酶将一种含氮中间产物羟胺氧化成亚硝酸盐。 叫做羟胺氧化还原酶。 我们打算完成酶结构的测定。 然后，通过研究酶上基团颜色的变化，并通过化学方法测量中间化合物的产生，我们将发现它如何能够作为这种不寻常反应的催化剂。 ***

Hooper 9316906 In soils, fertilizer ammonia is oxidized to nitrite (NH3 + 1.5 02- HNO2 + H2) by the chemoautotrophic nitrifying bacterium Nitrosomonas europaea.. Nitrite is oxidized by Nitrobacter to nitrate, a primary source of N for food protein in non-leguminous crops. Of great economic transformation of most food nitrogen is carried out by Nitrosomonas. Of great economic importance is loss of N in soils as N-gases produced by Nitrosomonas during oxidation of NH3 or by reduction of nitrate by denitrifying bacteria. Control of agricultural loss by denitrification is attempted by the use of inhibitors of ammonia oxidation by Nitrosomonas. This gives significance to improved knowledge of the mechanism of oxidation of ammonia. NH3 is oxygenated by O2 to NH2OH which is then oxidized (NH2OH + H20- HN02 + 4e- + 4H+) by the enzyme hydroxylamine oxidoreductase "HAO". HAO is a large and unusually complex hemoprotein (7 c-hemes and 1 substrate binding. "P460" group per 63 kDa protein). Four electron pass from HAO to a tetraheme cytochrome c-554. Two electrons pass from cytochrome c-554 in a separate electron transfer chain to the ammonia oxidizing reaction. Two additional electrons pass to a membrane terminal oxidase, a dissimilatory nitrite reductase (during growth at low oxygen), to an ATP- dependent NAD reductase or a peroxidase (to scavange peroxide). The goal of this project is the analysis of the enzyme HAo. We intend to determine details of the structure of HAO with particular attention to the active site and mechanism of turnover. The approach involves optical spectroscopy, peptide analysis, kinetics, suicide substrates, electron paramagnetic resonance spectroscopy, Mossbauer spectroscopy and X-ray crystallographic analysis. %%% The soil and water bacterium, Nitrosomonas, is critical to the cycle of nitrogen in nature, to the production of a greenhouse and ozone destroying gas, to nitrogen availability in agriculture and in the degradation of chlori nated pollutants. This project is involved in the study of the structure of the biological catalyst which enables the organism to perform those roles. The enzyme oxidizes one of the nitrogenous intermediates, hydroxylamine, to nitrite. Is called hydroxylamine oxidoreductase. We intend to complete the determination of the structure of the enzyme. Then, by studying changes in the color of groups on the enzyme and by measuring the production of intermediate compounds by chemical means, we will find out how it is able to act as a catalyst for this unusual reaction. ***