Interaction of aliphatic N-hydroxylamines with microsomal cytochrome P450: nature of the different derived complexes and inhibitory effects on monoxygenases activities.

Primary N-hydroxylamines, RR′R″CNHOH, produce difference spectra of liver microsomes from variously pretreated rats with peaks around 420 nm and troughs around 392 nm which are interpreted as the result of the hydroxylamines binding to cytochrome P450-Fe (III) through their oxygen atom. The hydroxylamines interact with dithionite-or NADPH-anaerobically reduced micro-somes giving peaks around 423 nm. In the presence of NADPH, oxygen and microsomes, all the hydroxylamines of the type RR'CHNHOH lead to 455 nm difference spectra which should correspond to cytochrome P450-Fe (II)-RR′CHNO complexes. These hydroxylamines also act as strong inhibitors of aniline hydroxylase, P-nitroanisole-O-demethylase and 7-ethoxycoumarin-O-dealkylase activities of PB-pretreated rat liver microsomes. In most cases, they are better inhibitors than metyrapone or SKF 525A. These inhibitory effects of hydroxylamines are related to their ability to lead to 455 nm absorbing complexes; For instance, 1-hydroxylamino-2phenyl-ethane exhibits the best apparent Ks for the 455 nm absorbing complex formation and is also the best inhibitor of microsomal $\text{7-}\text{ethoxycoumarin}\text{-O-}\text{dealkylase}\text{(}\text{I}{}_{50}\text{= 0.5 μ}\text{M}\text{)}$.