PEROXYNITRITE REACTION WITH CARBON DIOXIDE BICARBONATE - KINETICS ANDINFLUENCE ON PEROXYNITRITE-MEDIATED OXIDATIONS/

Peroxynitrite is a strong oxidant produced in vivo as the reaction pro duct of superoxide anion and nitric oxide (k similar to 5 x 10(9) M(-1 ) s(-1)) and can be formed and mediate reactions in the extracellular environment, It has recently been reported that peroxynitrite and carb on dioxide react in a second-order process (S. V. Lymar and K. Hurst ( 1995) J. Am, Chem, Sec. 117, 8867-8868). Since one of the most abundan t constituents of the extracellular milieu is bicarbonate anion (25 mM in plasma) which is in equilibrium with carbon dioxide (1.3 mM in pla sma) we have further studied the kinetics of the reaction between pero xynitrite and carbon dioxide/bicarbonate and the effect of bicarbonate on different peroxynitrite-mediated oxidations. The apparent second-o rder rate constant for the reaction is (2.3 +/- 0.1) x 10(3) M(-1) s(- 1) at 37 degrees C and pH 7.4 and a pH-independent second-order rate c onstant of (5.8 +/- 0.2) x 10(4) M(-1) s(-1) at 37 degrees C was obtai ned considering peroxynitrite anion and carbon dioxide as the reacting species, The enthalpy and entropy of activation are Delta H-# = +10.7 +/- 0.8 kcal mol(-1) and Delta S-# = -6.5 +/- 0.5 cal mol(-1) K-1, re spectively. The presence of bicarbonate had variable influence on pero xynitrite-mediated oxidations, While bicarbonate significantly enhance d peroxynitrite-mediated nitration of aromatics, it partially inhibite d the oxidation of thiols, dimethylsulfoxide, oxyhemoglobin, and cytoc hrome c(+2) and totally inhibited the hydroxylation of benzoate, Spont aneous chemiluminescence studies suggest the formation of bicarbonate radicals during the interactions of peroxynitrite with carbon dioxide/ bicarbonate. Our results support that peroxynitrite anion rapidly reac ts with carbon dioxide to yield an adduct (ONOOCO2-) which can partici pate in oxidation and nitration processes, thus redirecting the primar y reactivity of peroxynitrite, (C) 1996 Academic Press, Inc.