GENERATION OF THIYL AND ASCORBYL RADICALS IN THE REACTION OF PEROXYNITRITE WITH THIOLS AND ASCORBATE AT PHYSIOLOGICAL PH

Electron spin resonance (ESR) spin trapping was utilized to investigat e the reaction of peroxynitrite with thiols and ascorbate at physiolog ical pH. The spin trap used was 5,5-dimethyl-1-pyrroline N-oxide (DMPO ). The reaction of peroxynitrite with DMPO generated 5,5-dimethylpyrro lidone-(2)-oxy-(1) (DMPOX). Formate enhanced the peroxynitrite decompo sition but did not generate any detectable amount of formate-derived f ree radicals. Thus, the spin trapping measurements provided no evidenc e for hydroxyl ((OH)-O-.) radical generation in peroxynitrite decompos ition at physiological pH. Thiols (glutathione, cysteine, and penicill amine) and ascorbate reacted with peroxynitrite to generate the corres ponding thiyl and ascorbyl radicals. The one-electron oxidation of thi ols by peroxynitrite may be one of the important mechanisms for peroxy nitrite-induced toxicity and ascorbate may provide a detoxification pa thway.