Effect of (NO)-N-center dot on the decomposition of peroxynitrite: Reaction of N2O3 with ONOO-

Nitric oxide reacts slowly with ONOO- (k < 1.3 x 10(-3) M-1 s(-1)), and the refore does not affect the stability of peroxynitrite at pH >12. A chain co nsumption of peroxynitrite by (NO)-N-. takes place at pH<12 through the rea ction of N2O3 with ONOO-, where the former is formed through two initiation steps: (i) autoxidation of (NO)-N-., which is the main process in alkaline solutions, and (ii) spontaneous decomposition of peroxynitrite. The effect of (NO)-N-. on the decomposition of peroxynitrite depends on the rate of t he reaction of ONOO- with N2O3 (propagation step) relative to that of the h ydrolysis of N2O3 (termination step). Therefore, rapid consumption of perox ynitrite occurs upon increasing the peroxynitrite concentration, decreasing the phosphate concentration, and lowering the pH, as the hydrolysis of N2O 3 is base-catalyzed. The rate constant of the reaction of ONOO- with N2O3 h as been determined in alkaline solutions to be (3.1 +/- 9.3) x 10(8) M-1 s( -1). The decomposition of ONOOH in acidic solutions is hardly affected by ( NO)-N-., as N2O3 does not react with ONOOH. Under physiological conditions, the reaction of (NO)-N-. with peroxynitrite cannot give rise to a chain co nsumption of peroxynitrite as the reaction of N2O3 with the relatively low concentrations of peroxynitrite cannot compete with the hydrolysis of N2O3.