Involvement of a Flavosemiquinone in the Enzymatic Oxidation of Nitroalkanes Catalyzed by 2-Nitropropane Dioxygenase
作者:Kevin Francis、Bethany Russell、Giovanni Gadda
DOI:10.1074/jbc.m411249200
日期:2005.2
isotope effects with 1,2-[(2)H(4)]nitroethane and 1,1,2-[(2)H(3) ethyl nitronate at pH 8 yielded normal and inverse effects on the k(cat)/K(m) value, respectively, and were negligible on the k(cat) value. The k(cat)/K(m) and k(cat) pH profiles with anionic nitronates showed the requirement of an acid, whereas those for neutral nitroalkanes were consistent with the involvement of both an acid and a base
2-硝基丙烷双加氧酶(EC 1.13.11.32)催化将硝基烷烃氧化为相应的羰基化合物和亚硝酸盐。在这项研究中,克隆了编码粗糙脉孢菌中酶的ncd-2基因,并在大肠杆菌中表达,并纯化了所得酶。尺寸排阻色谱,热变性和质谱分析显示2-硝基丙烷双加氧酶是80 kDa的同型二聚体,每摩尔亚基含有一摩尔非共价结合的FMN,并且不含铁。对于中性硝基链烷烃和除硝酸-1-丙酯和-2-硝酸丙酯以外的阴离子磺酸盐,使用超氧化物歧化酶建立了涉及超氧化物的非酶促自由基反应,在酶活性位点发生了底物氧化。该酶对硝酸盐比对硝基烷更具特异性,这是由用2-硝基丙烷和烷基链长在2至6个碳原子之间的伯硝基烷确定的二级速率常数k(cat)/ K(m)所暗示的。经测定,以中性或阴离子形式的2-硝基丙烷,硝基乙烷,硝基丁烷和硝基己烷的稳态动力学机理是连续的,这与在羰基产物释放之前氧与还原形式的酶反应是一致的。以亚硝酸乙酯为底物的酶监控