Xanthine oxidase/hydrogen peroxide generates sulfur trioxide anion radical (SO.−3) from sulfite (SO2−3)

AbstractIn the presence of hydrogen peroxide (H2O2), xanthine oxidase has been found to catalyze sulfur trioxide anion radical (SO.−3) formation from sulfite anion (SO2−3). The SO.−3 radical was identified by ESR (electron spin resonance) spin trapping, utilizing 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) as the spin trap. Inactivated xanthine oxidase does not catalyze SO.−3 radical formation, implying a specific role for this enzyme. The initial rate of SO.−3 radical formation increases linearly with xanthine oxidase concentration. Together, these observations indicate that the SO.−3 generation occurs enzymatically. These results suggest a new property of xanthine oxidase and perhaps also a significant step in the mechanism of sulfite toxicity in cellular systems