Comparative Studies on the N-Oxidation of Aniline and N, N-Dimethylaniline by Rabbit Liver Microsomes

Abstract

1. Rate studies of N-oxidation of aniline and N,N-dimethylaniline by rabbit liver microsomal preparations were performed at different pH values. The apparent pKs of the free functional groups were 7.2 and 6.9, respectively, at 26°. The apparent heats of ionization of these groups varied from 26.8 to 31.8 kJ mol⁻¹.

2. Photo-oxidation of the microsomal mixed function oxidase resulted in rapid loss of N-oxygenating activity. The enzyme was markedly protected from inactivation by the presence of aniline or N,N-dimethylaniline. The apparent K_D values for protection were close to the K_m and K_s values for the individual arylamines. The pH profiles of the initial rates of photo-inactivation resembled the titration curves of groups with an apparent pK_a between 6.0 and 6.2.

3. The N-oxidase was strongly inhibited by diethyl pyrocarbonate at pH 6.0. Catalytic capacity was partially restored by treatment with neutral hydroxyl-amine. Pyridine protected the enzyme from acylation.

4. A close relationship exists between the N-hydroxylation of aniline and the N-oxide formation from N,N-dimethylaniline with respect to sensitivity to photo-oxidation, reactivity to protective substrates and susceptibility to carb-ethoxylation.