Metabolism of carcinogenic N-nitroso-N-methylaniline by purified cytochromes P450 2B1 and P450 2B2.
N-Nitroso-N-methylaniline (NMA) is an esophageal carcinogen in the rat. The in vitro enzymatic metabolism of NMA was investigated using cytochromes P450 2B1 and P450 2B2, isolated from liver microsomes of rats pretreated with phenobarbital (PB), reconstituted with NADPH-cytochrome P450 reductase and dilauroylphosphatidylcholine. Formaldehyde is produced by both cytochromes P450 (P450). NMA is a better substrate for P450 2B1 than for P450 2B2. The maximal velocity (Vmax) values are 3.3 and 1.6 nmol HCHO/min per nmol P450 for P450 2B1 and P450 2B2, respectively. Beside formation of formaldehyde, aniline and p-aminophenol (p-AP) are found to be metabolites formed from NMA by both P450 isoenzymes. P450 2B1 also affords phenol, while none was found with the P450 2B2 isoenzyme. Phenol formation presumably arose from direct alpha-C-hydroxylation of NMA via a benzenediazonium ion (BDI) intermediate. The results suggest strongly that P450 2B1 catalyzes both alpha-C-hydroxylation and denitrosation of NMA while P450 2B2 catalyzes only denitrosation. Therefore, the P450 2B1 isoenzyme participates in the activation of NMA to the ultimate carcinogenic BDI.
Stiborová
M
M
Department of Biochemistry, Faculty of Natural Sciences, Charles University, Albertov, Czech Republic.
Hansíková
H
H
Frei
E
E
D000814:Aniline Compounds / Q000378:metabolism*; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D019362:Cytochrome P-450 CYP2B1 / Q000378:metabolism* / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism* / Q000494:pharmacology; D009602:Nitrosamines / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D013250:Steroid Hydroxylases / Q000378:metabolism* / Q000494:pharmacology
D000814:Aniline Compounds; D009602:Nitrosamines; D003577:Cytochrome P-450 Enzyme System; C014102:N-methyl-N-nitrosoaniline; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; D019362:Cytochrome P-450 CYP2B1; C025619:steroid 16-beta-hydroxylase; C023650:aniline; D010634:Phenobarbital