ABSTRACT
Peroxynitrite is generated by the second-order reaction between nitric oxide ( NO) and superoxide. The rate constant is 6.7 x 109 M-1s~\ three times faster than the reaction between superoxide and superoxide dismutase and 30 times as rapid as the reaction between -NO and oxyhemoglobin (1). Hence, formation of peroxynitrite is kinetically favored over competing reactions in vivo when both superoxide and NO are available. The pKa of peroxynitrite (ONOO-) is 6.8, and at pH 7.4 approximately 25% will be protonated to form peroxynitrous acid (ONOOH). Peroxynitrite is a powerful oxidant that can readily react with many cellular components. The peroxynitrite anion is stable at alkaline pH; however, peroxynitrous acid isomerizes to nitrate at the rate of 0.6 sec-1 in phosphate buffer at 37°C (2).
