An electron spin resonance study of a novel radical cation produced during the horseradish peroxidase-catalyzed oxidation of tetramethylhydrazine

The one-electron oxidation of tetramethylhydrazine by the horseradish peroxidase/hydrogen peroxide system forms a novel stable radical cation. The steady-state concentration of the tetramethylhydrazine radical cation increases with the hydrazine concentration, but depends on neither the enzyme concentration nor the hydrogen peroxide concentration. A mechanism involving the enzymatic one-electron oxidation of the tetramethylhydrazine radical cation to a dication is proposed to account for the enzyme independency. Incubations containing horseradish peroxidase, hydrogen peroxide and tetramethylhydrazine produced formaldehyde which was found to increase with either HRP or tetramethylhydrazine concentration. The cation radical, the dication, and the imine (the deprotonated dication) are proposed as intermediates in the mechanism of formaldehyde production.