Demethylation and denitrosation of nitrosamines by cytochrome P-450 isozymes.
Demethylation and denitrosation of nitrosamines by cytochrome P-450 isozymes.
复制标题
细胞色素 P-450 同工酶对亚硝胺进行去甲基化和脱亚硝化。
DOI：
10.1016/0003-9861(85)90476-x
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发表时间：
1985
影响因子：
3.9
通讯作者：
Yang,CS
中科院分区：
文献类型：
--
作者：
Tu,YY;Yang,CS
在由细胞色素P-450同工酶组成的重建单加氧酶系统中研究了亚硝胺的代谢，该系统是从乙醇和苯巴比妥处理的大鼠的肝微粒体中纯化的。乙醇诱导的同工酶（P-450et）能够有效催化N-亚硝基二甲胺（NDMA）的去甲基化，Km为2.4 mm，Vmax为7.2 nmol min−1nmolP-450−1，但对N-亚硝基甲基苄胺和N-亚硝基甲基苯胺的活性较差。苯巴比妥诱导形式 (P-450b) 对 NDMA 代谢无效，但对催化 N-亚硝基甲基苯胺的脱甲基化具有活性，估计 Km 为 0.08 mm，aVmax 为 7.2 nmol min−1nmol−1。P-450 还催化 NDMA 脱亚硝化，aKm 为 13.6 mm，aVmax 为1.36 nmol min−1nmol−1。使用对照肝微粒体，观察到 NDMA 去甲基化和脱亚硝化的多个 Km 值。超氧化物歧化酶的作用表明超氧自由基参与了 NDMA 的代谢，在不同的单加氧酶系统中，超氧化物歧化酶抑制了 43% 至 73% 的脱亚硝化作用和 13% 至 22% 的脱甲基化作用。 2-苯乙胺和3-氨基-1,2,4-三唑强烈抑制P-450et依赖性NDMA去甲基化；这些化合物以前被认为不是 P-450 依赖性反应的抑制剂，但被发现可以抑制微粒体 NDMA 脱甲基酶。目前的结果确立了 P-450 在亚硝胺代谢中的作用，并有助于澄清该研究领域之前的一些困惑。
Metabolism of nitrosamines was studied in a reconstituted monooxygenase system composed of cytochromeP-450 isozymes purified from liver microsomes of ethanol- and phenobarbital-treated rats. The ethanol-induced isozyme (P-450et) was efficient in catalyzing the demethylation ofN-nitrosodimethylamine (NDMA), with aKmof 2.4 mmandVmaxof 7.2 nmol min−1nmolP-450−1, but less active withN-nitrosomethylbenzylamine andN-nitrosomethylaniline. The phenobarbital-induced form (P-450b) was ineffective in NDMA metabolism but was active in catalyzing the demethylation ofN-nitrosomethylaniline, with an estimatedKmof 0.08 mmand aVmaxof 7.2 nmol min−1nmol−1.P-450etalso catalyzed the denitrosation of NDMA with aKmof 13.6 mmand aVmaxof 1.36 nmol min−1nmol−1. With control liver microsomes, multipleKmvalues were observed for the demethylation and denitrosation of NDMA. Involvement of superoxide radicals in the metabolism of NDMA was suggested by the action of superoxide dismutase, which inhibited the denitrosation by 43 to 73% and the demethylation by 13 to 22% in different monooxygenase systems. TheP-450et-dependent NDMA demethylation was strongly inhibited by 2-phenylethylamine and 3-amino-1,2,4-triazole; these compounds were previously believed not to be inhibitors ofP-450-dependent reactions but were found to inhibit microsomal NDMA demethylase. The present results establish the role ofP-450 in nitrosamine metabolism and help to clarify some of the previous confusion in this area of research.