O'Brien E M, Tipton K F, McCrodden J M, Youdim M B
Department of Biochemistry, Trinity College, Dublin, Ireland.
Biochem Pharmacol. 1994 Feb 11;47(4):617-23. doi: 10.1016/0006-2952(94)90123-6.
The interactions of the anticonvulsant drug milacemide (2-n-pentylaminoacetamide) with rat liver mitochondrial monoamine oxidases-A and -B have been studied. The compound acts as a substrate for the B-form of the enzyme, with an apparent Km value of 49 +/- 4.7 microM and a Vmax value of 1.1 +/- 0.2 nmol/min/mg. It is also a time-dependent irreversible inhibitor of that enzyme. Any activity of monoamine oxidase-A towards this substrate was too low to allow accurate determinations to be made by either luminometric determination of H2O2 formation or spectrophotometric coupling of aldehyde formation to NAD+ reduction in the presence of aldehyde dehydrogenase. Milacemide was a reversible competitive inhibitor towards monoamine oxidase-A. The inhibitor constant (Ki) was 115 +/- 35 microM indicating a higher affinity than that towards monoamine oxidase-B, which was also competitively inhibited in the absence of enzyme-inhibitor preincubation (Ki = 331 +/- 185 microM). Determination of the formation of H2O2 and the aldehyde product of the oxidative cleavage of milacemide by purified monoamine oxidase-B from ox liver indicated that cleavage resulted solely in the formation of pentanal and glycinamide. There was no evidence for alternative cleavage to pentylamine and oxamaldehyde.
已对抗惊厥药物米拉酰胺（2-正戊基氨基乙酰胺）与大鼠肝脏线粒体单胺氧化酶A和B的相互作用进行了研究。该化合物是该酶B型的底物，表观Km值为49±4.7微摩尔，Vmax值为1.1±0.2纳摩尔/分钟/毫克。它也是该酶的时间依赖性不可逆抑制剂。单胺氧化酶A对该底物的任何活性都太低，以至于在存在醛脱氢酶的情况下，通过光度法测定H2O2形成或分光光度法将醛形成与NAD+还原偶联来进行准确测定是不可能的。米拉酰胺是单胺氧化酶A的可逆竞争性抑制剂。抑制常数（Ki）为115±35微摩尔，表明其亲和力高于对单胺氧化酶B的亲和力，在不存在酶-抑制剂预孵育的情况下，单胺氧化酶B也受到竞争性抑制（Ki = 331±185微摩尔）。通过从牛肝脏中纯化的单胺氧化酶B测定米拉酰胺氧化裂解产生的H2O2和醛产物，表明裂解仅产生戊醛和甘氨酰胺。没有证据表明会裂解为戊胺和草酰醛。
