Yamasaki R B, Silverman R B
Biochemistry. 1985 Nov 5;24(23):6543-50. doi: 10.1021/bi00344a036.
The effect of 18 different amines, two mercaptans, and two alcohols on the reactivation of N-cyclopropylbenzylamine- (N-CBA-) inactivated bovine liver monoamine oxidase (MAO) is described. All of the compounds that reactivate the enzyme produce a time-dependent pseudo-first-order return of enzyme activity and exhibit saturation kinetics. There is no direct correlation between the ability of a compound to serve as a substrate for native MAO and its ability to reactivate N-CBA-inactivated MAO. Amines containing an aromatic moiety, in general, are better reactivators than the aliphatic amines. The amine must be primary or secondary in order for reactivation to occur. The distance between the aromatic portion and the amino group is critical to the reactivation properties of the compound. The mercaptans and alcohols do not reactivate N-CBA-inactivated MAO, nor do they interfere with the reactivation reaction by benzylamine. Three mechanisms for the reactivation reaction are considered. One involves initial Schiff base formation with the active site adduct produced by N-CBA inactivation of MAO followed by base-catalyzed beta-elimination to the imine of acrolein. The second mechanism is the same as the first except no prior Schiff base formation is invoked. The third mechanism is an SN2 displacement by the amine of the active site amino acid residue attached to the adduct. Experiments are carried out to exclude the SN2 mechanism. The results of the reactivation experiments favor the Shiff base mechanism.
本文描述了18种不同的胺、两种硫醇和两种醇对N-环丙基苄胺（N-CBA）灭活的牛肝单胺氧化酶（MAO）再活化的影响。所有能使该酶再活化的化合物都会使酶活性呈现出时间依赖性的准一级恢复，并表现出饱和动力学。一种化合物作为天然MAO底物的能力与其使N-CBA灭活的MAO再活化的能力之间没有直接关联。一般来说，含有芳香部分的胺比脂肪族胺是更好的再活化剂。胺必须是伯胺或仲胺才能发生再活化。芳香部分与氨基之间的距离对化合物的再活化特性至关重要。硫醇和醇不会使N-CBA灭活的MAO再活化，它们也不会干扰苄胺的再活化反应。本文考虑了再活化反应的三种机制。一种机制涉及与MAO被N-CBA灭活产生的活性位点加合物首先形成席夫碱，随后通过碱催化的β-消除反应生成丙烯醛的亚胺。第二种机制与第一种相同，只是不涉及预先形成席夫碱。第三种机制是胺对与加合物相连的活性位点氨基酸残基进行SN2取代。开展了实验以排除SN2机制。再活化实验的结果支持席夫碱机制。
