Studies on the mechanism of hepatic microsomal N-oxide formation. N-oxidation of NN-dimethylaniline by a reconstituted rabbit liver microsomal cytochrome P-448 enzyme system

Abstract

The N-oxidation of NN-dimethylaniline was studied by using a reconstituted rabbit liver microsomal enzyme system consisting of highly purified cytochrome P-448, NADPH-cytochrome c reductase and lipid factor. Both cytochrome P-448 and NADPH-cytochrome c reductase were required for optimum N-oxygenating activity; the catalytic capacity of the reductase fraction for supporting N-oxide formation varied with the isolation procedure applied. Addition of microsomal lipids to the assay media stimulated N-oxidation of the arylamine. N-Oxide formation appeared to be not generally controlled by electron transfer from cytochrome b5 to cytochrome P-448. The present work confirms that cytochrome P-448 can mediate about 44% of the rabbit liver microsomal N-oxidation of NN-dimethylaniline, thus reinforcing the existence of at least two distinct tertiary amine N-oxidases, i.e. haemoprotein and flavoprotein oxidase, in liver microsomal fractions.