Prema K, Gopinathan K P
Biochem J. 1974 Dec;143(3):613-24. doi: 10.1042/bj1430613.
A mono-oxygenase catalysing the conversion of 2-ethyl-4-thioisonicotinamide (ethionamide) into its sulphoxide was purified from guinea-pig liver homogenates. The enzyme required stoicheiometric amounts of oxygen and NADPH for the sulphoxidation reaction. The purified protein is homogeneous by electrophoretic, antigenic and chromatographic criteria. The enzyme has mol.wt. 85000 and it contains 1g-atom of iron and 1mol of FAD per mol, but not cytochrome P-450. The enzyme shows maximal activity at pH7.4 in a number of different buffer systems and the K(m) values calculated for the substrate and NADPH are 6.5x10(-5)m and 2.8x10(-5)m respectively. The activation energy of the reaction was calculated to be 36kJ/mol. Under optimal conditions, the molecular activity of the enzyme (mol of substrate oxidized/min per mol of enzyme) is calculated to be 2.1. The oxygenase belongs to the class of general drug-metabolizing enzymes and it may act on different compounds which can undergo sulphoxidation. The mechanism of sulphoxidation was shown to be mediated by superoxide anions.
从豚鼠肝脏匀浆中纯化出一种单加氧酶，它可催化2-乙基-4-硫代异烟酰胺（乙硫异烟胺）转化为其亚砜。该酶在亚砜氧化反应中需要化学计量的氧气和NADPH。通过电泳、抗原性和色谱分析标准，纯化后的蛋白质具有均一性。该酶的分子量为85000，每摩尔含有1克原子铁和1摩尔FAD，但不含细胞色素P-450。在多种不同缓冲系统中，该酶在pH7.4时显示出最大活性，计算得出的底物和NADPH的K(m)值分别为6.5×10(-5)m和2.8×10(-5)m。该反应的活化能经计算为36kJ/mol。在最佳条件下，该酶的分子活性（每摩尔酶每分钟氧化的底物摩尔数）经计算为2.1。这种加氧酶属于一般药物代谢酶类，它可能作用于不同的可进行亚砜氧化的化合物。亚砜氧化机制显示是由超氧阴离子介导的。
