title: N-Hydroxylation enzymes of carcinogenic aminoazo dyes: possible involvement of cytochrome P-448.
abstract: N-Hydroxylation reactions of 3'-methyl-N,N-dimethyl-4-aminoazobenzene (3'-Me-DAB) and 3'-methyl-N-methyl-4-aminoazobenzene (3'-Me-MAB) were studied by measuring the nitroxide radical generated from N-hydroxylated products of these aminoazo compounds. N-Hydroxylation activity was remarkably high in the microsomes from 3-methylcholanthrene (3-MC)-treated rats, whereas phenobarbital (PB) treatment had a slightly enhancing effect on the N-hydroxylation of 3'-Me-DAB and a rather inhibitory effect on that of 3'-Me-MAB. Either NADPH or NADH was effective for the N-hydroxylation of 3'-Me-MAB, though the former was slightly more effective. For the reaction of 3'-Me-DAB the effect of NADPH and NADH was additive, but this was not the case for 3'-Me-MAB. Carbon monoxide, metyrapone and 2-diethylaminoethyl-2,2-diethylvalerate hydrochloride (SKF-525-A), inhibitors of cytochrome P-450, had no inhibitory effect on the N-hydroxylation of 3'-Me-DAB and 3'-Me-MAB. On the other hand, alpha-naphthoflavone, an inhibitor of cytochrome P-448, considerably inhibited the N-hydroxylation of these aminoazo dyes. In the case of partially purified mixed function amine oxidase (MFAO), 1-(1-naphthyl)-2-thiourea, an inhibitor of MFAO, completely inhibited the N-hydroxylation of 3'-Me-MAB as well as the N-oxidation of dimethylaniline. On the other hand, in a microsomal system the inhibition of the N-hydroxylation was at most 40% at the concentration giving complete inhibition of the N-oxidation of dimethylaniline. From these results, it is concluded that, in addition to MFAO, cytochrome P-448 is involved in the N-hydroxylation of MAB.
mesh_terms: D000818:Animals; D001391:Azo Compounds / Q000378:metabolism*; D019388:Cytochrome P-450 CYP1A2; D003580:Cytochromes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005609:Free Radicals; D006900:Hydroxylation; D008297:Male; D008749:Methyldimethylaminoazobenzene / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D010128:p-Aminoazobenzene / Q000031:analogs & derivatives / Q000378:metabolism*; D004124:p-Dimethylaminoazobenzene / Q000031:analogs & derivatives*
chemical_list: D001391:Azo Compounds; D003580:Cytochromes; D005609:Free Radicals; D009243:NAD; D009249:NADP; D008749:Methyldimethylaminoazobenzene; D010128:p-Aminoazobenzene; C008468:3-methyl-4-methylaminoazobenzene; D004124:p-Dimethylaminoazobenzene; C017170:Cyp1a2 protein, rat; D019388:Cytochrome P-450 CYP1A2; D000587:Oxidoreductases Acting on CH-NH Group Donors; C019668:amine oxidase, mixed function