Ziegler D M, Ansher S S, Nagata T, Kadlubar F F, Jakoby W B
Clayton Foundation Biochemical Institute, Department of Chemistry, University of Texas, Austin 78712.
Proc Natl Acad Sci U S A. 1988 Apr;85(8):2514-7. doi: 10.1073/pnas.85.8.2514.
Two amine N-methyltransferases isolated from rabbit liver catalyze S-adenosylmethionine-dependent N-methylation of benzidine and 4-aminobiphenyl but not of 4-aminoazobenzene or 2-aminobiphenyl. The enzymatic reaction products were analyzed and found to be identical to synthetic N-methylbenzidine and N-methyl-4-aminobiphenyl. N-Methylation may be a critical step in the metabolic activation of primary arylamines because N-methylarylamines, unlike primary arylamines, are readily N-oxygenated by the NADPH- and oxygen-dependent microsomal flavin-containing monooxygenase. Kinetic studies carried out with the purified porcine liver monooxygenase demonstrate that, while activity with primary arylamines could not be detected, N-methyl derivatives of benzidine, 4-aminoazobenzene, and 4-aminobiphenyl are substrates. Products formed from N-methyl-4-aminobiphenyl had the properties of the hydroxylamine and/or nitrone in that the enzyme- and time-dependent incubation product(s) reduced Fe3+ to Fe2+, and formaldehyde was formed during the course of the reaction. These data suggest that N-methyl-4-aminobiphenyl is oxidized to N-hydroxy-N-methyl-4-aminobiphenyl, which can undergo further oxidation to a nitrone that hydrolyzes to formaldehyde and N-hydroxy-4-aminobiphenyl.
从兔肝脏中分离出的两种胺N-甲基转移酶催化S-腺苷甲硫氨酸依赖性的联苯胺和4-氨基联苯的N-甲基化反应，但不催化4-氨基偶氮苯或2-氨基联苯的N-甲基化反应。对酶促反应产物进行分析，发现其与合成的N-甲基联苯胺和N-甲基-4-氨基联苯相同。N-甲基化可能是伯芳胺代谢活化的关键步骤，因为与伯芳胺不同，N-甲基芳胺很容易被依赖于NADPH和氧气的微粒体含黄素单加氧酶进行N-氧化。用纯化的猪肝单加氧酶进行的动力学研究表明，虽然未检测到其对伯芳胺的活性，但联苯胺、4-氨基偶氮苯和4-氨基联苯的N-甲基衍生物是底物。由N-甲基-4-氨基联苯形成的产物具有羟胺和/或硝酮的性质，即酶促和时间依赖性孵育产物将Fe3+还原为Fe2+，并且在反应过程中形成甲醛。这些数据表明，N-甲基-4-氨基联苯被氧化为N-羟基-N-甲基-4-氨基联苯，后者可进一步氧化为硝酮，硝酮水解为甲醛和N-羟基-4-氨基联苯。
