title: Role of cytochrome P-450 and flavin-containing monooxygenase in the N-hydroxylation of N-methyl-4-aminoazobenzene in rat liver: analysis with purified enzymes and antibodies.
abstract: By means of high pressure liquid chromatography, the role of flavin-containing monooxygenase (FMO) and cytochrome P-450 (cyt. P-450) in the metabolism of N-methyl-4-aminoazobenzene (MAB) by rat liver microsomes in vitro was studied with the help of antibodies and a chemical inhibitor. Antibody against cyt. P-488 from 3-methylcholanthrene-treated rats (MC-P-448) decreased the formation of N-hydroxy-N-methyl-4-aminoazobenzene (N-OH-MAB) by about 30% in microsomes from MC-treated rats (MC-microsomes), but showed no inhibitory effect on the formation of N-OH-MAB in microsomes from untreated rats (untreated microsomes) or in microsomes from phenobarbital-treated rats (PB-microsomes). Antibody against cyt. P-450 from PB-treated rats did not inhibit N-hydroxylation of MAB by any of the microsomes tested. A competitive inhibitor of FMO, methimazole, inhibited the N-hydroxylation of MAB by 65% in the case of MC-microsomes, and the residual activity was inhibited completely by anti-NADPH-cytochrome P-450 reductase (anti-fPT) antibody. These results indicate that in MC-microsomes, the N-hydroxylation of MAB is catalyzed by both FMO and MC-P-448, but in untreated and PB-microsomes the reaction is catalyzed exclusively by FMO.
mesh_terms: D000818:Animals; D000936:Antigen-Antibody Complex; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D001391:Azo Compounds / Q000378:metabolism*; D001711:Biotransformation; D002250:Carbon Radioisotopes; D002273:Carcinogens / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D006900:Hydroxylation; D007106:Immune Sera; D007700:Kinetics; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D010128:p-Aminoazobenzene / Q000031:analogs & derivatives / Q000378:metabolism*
chemical_list: D000936:Antigen-Antibody Complex; D001391:Azo Compounds; D002250:Carbon Radioisotopes; D002273:Carcinogens; D007106:Immune Sera; D008748:Methylcholanthrene; D010128:p-Aminoazobenzene; C005202:N-methyl-4-aminoazobenzene; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases