Comparative Studies on theN-Oxidation of Aniline andN,N-Dimethylaniline by Rabbit Liver Microsomes

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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 KD values for protection were close to the Km and Ks values for the individual arylamines. The pH profiles of the initial rates of photo-inactivation resembled the titration curves of groups with an apparent pKa 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.

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