Electron acceptor function of O 2 in radical N-demethylation reactions catalyzed by hemeproteins

Abstract

In aerobic solutions, O 2 consumption correlated well with N-demethylation of N,N-dimethyl- p -toluidine catalyzed by horseradish peroxidase, in the presence or absence of H 2O 2. In the absence of added H 2O 2, superoxide dismutase stimulated, and catalase inhibited, both reactions; in the presence of H 2O 2, argon inhibition of formaldehyde production increased with increasing concentration of horseradish peroxidase. These results provide evidence for competing reactions of the enzymatically-generated substrate radical: oxidation by O 2 increases formaldehyde production, while radical dimerization decreases the yield of this product. Implications of these findings for similar reactions catalyzed by microsomal cytochrome P-450 are suggested.