DIRECT DETECTION OF THE SULFUR-TRIOXIDE RADICAL-ANION DURING THE HORSERADISH-PEROXIDASE HYDROGEN-PEROXIDE OXIDATION OF SULFITE (AQUEOUS SULFUR-DIOXIDE)

Abstract

The ESR spectrum of .ovrhdot.SO3- is observed directly during the oxidation of (bi)sulfite to sulfate by horseradish peroxidase. This radical exhibited a single line at g = 2.0031. The .ovrhdot.SO3- radical was trapped with nitrosobenzene yielding an ESR spectrum with coupling constants AN = 12.3 G, .**GRAPHIC**. = .**GRAPHIC**. =2.4 G and .**GRAPHIC**. = 0.9 G, and a g-value of 2.0053. .ovrhdot.SO3- was an intermediate in the 2-step reduction of peroxidase compound by (bi)sulfite at physiological pH. At low pH, no .ovrhdot.SO3- was observed, which indicated a direct, 1-step, 2 electron reduction of compound. The pH at which the mechanism changed depended on the isoenzymes present. The radical reacted rapidly with O2 as evidenced by the absence of an ESR spectrum when O2 was present and by O2 uptake measurements.