The role of cytochrome P-450 in the dual pathways of N-demethylation of N,N-dimethylaniline by hepatic microsomes

The role of cytochrome P-450 in the demethylation of N,N'-dimethylaniline (DMA) has been investigated by studying carbon monoxide (CO) inhibition and its reversal by light. Two distinct pathways of N-demethylation are present in hepatic microsomes from phenobarbital-(PB) and 3-methylcholanthrene-(3-MC) induced rats. Pathway A, the demethylation of DMA, is catalysed by a microsomal cytochrome P-450 system similar to the one we have reported for the dealkylation of benzphetamine and 3-ethylmorphine, in that there is a maximal, although weak, light reversal of CO inhibition by wavelengths of light around 445 nm. The second pathway consists of two enzyme steps (pathways B + C). Pathway B is the step in which the N-oxide of DMA, N,N'-dimethylaniline N-oxide (DMAO) is formed and this step is catalysed by the flavin amine mixed-function oxidase described by Ziegler and his co-workers. Pathway C, the demethylation of DMAO, requires a cytochrome P-450 with rather unusual properties. This reaction is inhibited by SKF 525A and CO, but is not significantly affected by the removal of oxygen even though CO strongly inhibits in this anaerobic atmosphere. Higher CO/O2 ratios (2:1 to 4:1) are required for inhibition equal to that of pathway A and light reversal of this inhibition is almost complete and maximally produced by wavelengths of light around 455 nm.