Babior B M, Peters W A
J Biol Chem. 1981 Mar 10;256(5):2321-3.
The enzyme responsible for the respiratory burst in human neutrophils is a membrane-bound oxidase that catalyzes the reduction of oxygen to O2- at the expense of a reduced pyridine nucleotide. We describe further properties of the solubilized oxidase. The rates of O2- production and NADPH consumption are consistent with the stoichiometry: 2 O2 + NADPH leads to 2 O2- + NADP The enzyme is highly specific for oxygen, failing to reduce several artificial electron acceptors including ferricyanide. FAD, an essential cofactor, binds tightly to the enzyme, as indicated by a Km of 61 nM. A requirement for a free --SH group is suggested by a 2-fold increase in activity in the presence of low concentrations of dithiothreitol; the higher dithiothreitol concentrations lead to inhibition. The solubilized enzyme is highly unstable, losing one-half its activity after 1 h at room temperature. Loss of activity is accelerated 2- to 3-fold by salts and EDTA. The substrate analog 2',5'-ADP is similar to other salts in its effect on the inactivation rate. ATP, on the other hand, causes loss of activity in seconds, raising the possibility that ATP is a physiological regulator of the catalytic activity of the enzyme.
人类中性粒细胞中负责呼吸爆发的酶是一种膜结合氧化酶，它以还原型吡啶核苷酸为代价催化氧气还原为超氧阴离子（O2-）。我们描述了可溶性氧化酶的更多特性。超氧阴离子（O2-）的产生速率和烟酰胺腺嘌呤二核苷酸磷酸（NADPH）的消耗速率与化学计量关系一致：2O2 + NADPH → 2O2- + NADP。该酶对氧气具有高度特异性，不能还原包括铁氰化物在内的几种人工电子受体。黄素腺嘌呤二核苷酸（FAD）作为一种必需的辅因子，与该酶紧密结合，其米氏常数（Km）为61 nM表明了这一点。低浓度二硫苏糖醇存在时活性增加2倍，提示该酶需要一个游离的巯基（-SH）基团；较高浓度的二硫苏糖醇会导致抑制作用。可溶性酶高度不稳定，在室温下1小时后活性丧失一半。盐和乙二胺四乙酸（EDTA）会使活性丧失加速2至3倍。底物类似物2',5'-二磷酸腺苷（2',5'-ADP）对失活速率的影响与其他盐类似。另一方面，三磷酸腺苷（ATP）会在数秒内导致活性丧失，这增加了ATP是该酶催化活性的生理调节剂的可能性。
