N-HYDROXYLATION ENZYMES OF CARCINOGENIC AMINOAZO DYES - POSSIBLE INVOLVEMENT OF CYTOCHROME P-448

  • 1 January 1982
    • journal article
    • research article
    • Vol. 73  (1) , 55-62
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. NADPH or NADH was effective for the N-hydroxylation of 3''-Me-MAB, although 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-525A), inhibitors of cytochrome P-450, had no inhibitory effect on the N-hydroxylation of 3''-Me-DAB and 3''-Me-MAB. .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 dimethylamine. 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. In addition to MFAO, cytochrome P-448 evidently is involved in the N-hydroxylation of MAB.