ABSTRACT
The aminopyrine cation free radical was proposed to be an intermediate in the N-demethylation leading to the formation of formaldehyde. Free radical metabolites must exist free of the enzyme; therefore, enzyme-xenobiotic transition states with free radical character are excluded. It would seem, therefore, that lactoperoxidase could be used as a model for most mammalian hemoprotein peroxidases. The significance of mammalian peroxidases in the metabolism of toxic chemicals depends on the availability of hydrogen peroxide. The oxidation of aminopyrine to its cation radical by metmyoglobin utilizes hydrogen peroxide as the source of oxidative equivalents in a similar manner to horseradish peroxidase. The azidyl radical is formed during the oxidation of azide by the catalase/hydrogen peroxide system as detected by the electron spin resonance spin-trapping technique. The oxidation of azide catalyzed by horseradish peroxidase, lactoperoxidase, and myeloperoxidase also forms azidyl radical.
