Metabolic denitrosation of N-nitroso-N-methylaniline: detection of amine-metabolites

The enzymatic denitrosation of N-nitroso-N-methylaniline (NMA) was investigated by measuring the resulting amine metabolites when NMA was incubated with liver microsomes of PB-pretreated mice. Aniline was found to be the main amine metabolite. Small amounts of the secondary amine, N-methylaniline (MA) and its metabolite, p-methylaminophenol (p-MAP), could also be detected. Incubation of MA resulted in the formation of aniline and p-MAP. The velocity of the metabolism of MA was somewhat faster than that of NMA. On the basis of the measured Vmax values the formation of aniline from MA or from NMA proceeded at nearly identical rates. The dissociation constants as a measure of binding affinity to cytochrome (cyt.) P-450 were determined by measuring the binding spectra. NMA has one Ks of 3.1 mM, whereas MA shows two apparent Ks values, 650 microM and 25 mM, respectively. The results are discussed in relation to the enzymatic mechanism of denitrosation of NMA.