Cerny Matthew A, Hanzlik Robert P
Department of Medicinal Chemistry, University of Kansas, Lawrence, KS, USA.
Arch Biochem Biophys. 2005 Apr 15;436(2):265-75. doi: 10.1016/j.abb.2005.02.020.
The inactivation of cytochrome P450 enzymes by cyclopropylamines has been attributed to a mechanism involving initial one-electron oxidation at nitrogen followed by scission of the cyclopropane ring leading to covalent modification of the enzyme. Herein, we report that in liver microsomes N-cyclopropylbenzylamine (1) and related compounds inactivate P450 to a large extent via formation of metabolic intermediate complexes (MICs) in which a nitroso metabolite coordinates tightly to the heme iron, thereby preventing turnover. MIC formation from 1 does not occur in reconstituted P450 systems with CYP2B1/2, 2C11 or 2E1, or in microsomes exposed to gentle heating to inactivate the flavin-containing monooxygenase (FMO). In contrast, N-hydroxy-N-cyclopropylbenzylamine (3) and N-benzylhydroxylamine (4) generate MICs much faster than 1 in both reconstituted and microsomal systems. MIC formation from nitrone 5 (PhCH = N(O)cPr) is somewhat faster than from 1, but very much faster than the hydrolysis of 5 to a primary hydroxylamine. Thus the major overall route from 1 to a P450 MIC complex would appear to involve FMO oxidation to 3, further oxidation by P450 and/or FMO to nitrone 5' (C2H4C = N(O)CH2Ph), hydrolysis to 4, and P450 oxidation to alpha-nitrosotoluene as the precursor to oxime 2 and the major MIC from 1.
环丙胺使细胞色素P450酶失活的机制被认为是，首先在氮原子处发生单电子氧化，随后环丙烷环断裂，导致酶的共价修饰。在此，我们报道在肝微粒体中，N-环丙基苄胺（1）及相关化合物通过形成代谢中间体复合物（MICs）在很大程度上使P450失活，其中亚硝基代谢物与血红素铁紧密配位，从而阻止周转。在含有CYP2B1/2、2C11或2E1的重组P450系统中，或在经温和加热使含黄素单加氧酶（FMO）失活的微粒体中，1不会形成MIC。相反，在重组系统和微粒体系统中，N-羟基-N-环丙基苄胺（3）和N-苄基羟胺（4）生成MIC的速度比1快得多。硝酮5（PhCH = N(O)cPr）形成MIC的速度比1稍快，但比5水解为伯羟胺的速度快得多。因此，从1到P450 MIC复合物的主要总体途径似乎涉及FMO氧化为3，再经P45氧化和/或FMO氧化为硝酮5'（C2H4C = N(O)CH2Ph），水解为4，以及P450氧化为α-亚硝基甲苯，作为肟2和1的主要MIC的前体。
