Yang C S, Patten C, Lee M J, Li M, Yoo J S, Pan J, Hong J
Department of Biochemistry, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark.
IARC Sci Publ. 1987(84):104-8.
The metabolism of several N-nitrosodialkylamines was studied using rat liver microsomes and purified cytochrome P450 isozymes in a reconstituted monooxygenase system. With purified acetone/ethanol-inducible cytochrome P450 (P450ac), high N-nitrosodimethylamine (NDMA) demethylase activity was observed. Cytochrome b5 was also involved in NDMA metabolism by decreasing the Km of NDMA demethylase. A close relationship between the demethylation and denitrosation of this substrate was observed. P450ac was also active in the metabolism of N-nitrosoethylmethylamine (NEMA), but was less active than phenobarbital-inducible cytochrome P450 (P450b) in the metabolism of N-nitrosobutylmethylamine (NBMA), especially in catalysing the debutylation reaction. Similar substrate specificity was demonstrated with liver microsomes from rats treated with other inducers. With different P450 isozymes and microsomes, a close relationship between metabolism and activation of nitrosamines to mutagens to V79 cells was demonstrated. DNA alkylation by NDMA in vitro was correlated with the rate of metabolism of these compounds, whereas DNA alkylation in vivo was more complex and was dose-dependent. The work demonstrates the importance of knowledge of the substrate specificity of cytochrome P450 isozymes in understanding the mechanisms of the metabolic activation of nitrosamines.
在重组单加氧酶系统中，利用大鼠肝微粒体和纯化的细胞色素P450同工酶研究了几种N-亚硝基二烷基胺的代谢。对于纯化的丙酮/乙醇诱导型细胞色素P450（P450ac），观察到较高的N-亚硝基二甲胺（NDMA）脱甲基酶活性。细胞色素b5也通过降低NDMA脱甲基酶的Km参与NDMA代谢。观察到该底物的脱甲基和脱亚硝化之间存在密切关系。P450ac在N-亚硝基乙甲胺（NEMA）的代谢中也具有活性，但在N-亚硝基丁甲胺（NBMA）的代谢中，其活性低于苯巴比妥诱导型细胞色素P450（P450b），尤其是在催化脱丁基反应方面。用其他诱导剂处理的大鼠的肝微粒体也表现出类似的底物特异性。对于不同的P450同工酶和微粒体，证明了亚硝胺代谢与激活为V79细胞诱变剂之间存在密切关系。NDMA在体外对DNA的烷基化与这些化合物的代谢速率相关，而体内DNA烷基化则更为复杂且呈剂量依赖性。这项工作证明了了解细胞色素P450同工酶底物特异性对于理解亚硝胺代谢激活机制的重要性。
