Contributions of human liver cytochrome P450 enzymes to the N-oxidation of 4,4'-methylene-bis(2-chloroaniline).
Contributions of human liver cytochrome P450 enzymes to the N-oxidation of 4,4'-methylene-bis(2-chloroaniline).
复制标题
人肝细胞色素 P450 酶对 4,4-亚甲基-双(2-氯苯胺) N-氧化的贡献。
DOI：
10.1093/carcin/13.2.217
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发表时间：
1992
期刊：
影响因子：
4.7
通讯作者：
Guengerich,FP
中科院分区：
文献类型：
--
作者：
Yun,CH;Shimada,T;Guengerich,FP
4，4‘-亚甲基-双(2-氯苯胺)(MOCA)可在啮齿动物和狗身上产生肿瘤，据报道，接触者膀胱癌的发病率增加。因此，确定参与Mocan氧化的人细胞色素P450(P450)酶是有意义的，Mocan氧化是形成亲电产物的主要反应。对人肝微粒体进行分级，并通过该程序监测Mocan氧化活性。免疫化学分析和N-末端氨基酸序列分析表明，活性最高的酶组分对应于P450 3A4。酵母重组蛋白P450 3A4也具有Mocan氧化活性。纯化的人肝P450 2A6具有催化活性，但抗P450 2A6对微粒体活性的抑制率为20%，而抗P450 3A4的抑制率高达75%。测定了一组人肝微粒体中P450 3A4(硝苯地平氧化)和P450 2A6(香豆素7-羟化)的标志物活性水平，并将两者与Mocan氧化率相关联。孕二烯和曲霉素能抑制近一半的微粒体Mocan羟化活性，而7，8-苯并黄酮仅有轻微的抑制作用。根据细菌SOS反应判断，抗P4503A4能抑制(高达80%)MOCA向遗传毒性产物的微粒体转化。结果表明，P450 3A4在人肝微粒体Mocan氧化中起主要作用，P450 2A6起次要作用。P4501A2催化了许多芳胺的羟基化，但作用不大。
4,4′-Methylene-bis(2-chloroaniline) (MOCA) can produce tumors in rodents and dogs and an increased incidence of bladder tumors has been reported in exposed workers. It is therefore of interest to identify the human cytochrome P450 (P450) enzymes involved in MOCAN-oxidation, the primary reaction involved in the formation of an electrophilic product. Human liver microsomes were fractionated and MOCAN-oxidation activity was monitored through the procedure. The most active enzyme fraction corresponded to P450 3A4, as determined by immunochemical assays andN-terminal amino acid sequence analysis. Yeast recombinant P450 3A4 also had MOCAN-oxidation activity. Purified human liver P450 2A6 showed catalytic activity; however, anti-P450 2A6 inhibited <20% of the microsomal activity while anti-P450 3A4 inhibited up to 75%. Levels of marker activities of both P450 3A4 (nifedipine oxidation) and P450 2A6 (coumarin 7-hydroxylation) were measured in a set of human liver microsomes and both were correlated with MOCAN-oxidation rates. Gestodene and troleandomycin inhibited up to half of the microsomal MOCAN-hydroxylation activity but 7,8-benzoflavone showed only slight inhibition. Anti-P450 3A4 inhibited (up to 80% of) the microsomal transformation of MOCA to a product genotoxic as judged by bacterial SOS response. The work indicates that P450 3A4 makes a major contribution to human liver microsomal MOCAN-oxidation, and P450 2A6 has a minor role. P450 1A2, which catalyzes the hydroxylatlon of many arylamines, does not contribute to a great extent.