Study of the kinetics of nitric oxide formation from nitrite dismutation

Recently it has been shown that nitric oxide (NO) can be formed in biological systems by a mechanism which is independent of nilric oxide synthase. NO can also be synthesized by dismutation of nitrous acid which is formed from the equilibrium reaction of nitrile with hydrogen ion Nitrite ion exists in biological fluids and tissues in concentrations on order of magnitude 10-100 uM and it can be a significant source of NO under acidotic conditions. Therefore we performed in vitro studies of this mechanism of NO generation at conditions of shifted equilibrium using Electron Paramagnetic Resonance spectroscopy (binding NO with the spin trap Fe-MGD) as well as chernoluminesence techniques (purging Ilie reaction media with inert gas). It was found that the overall reaction is second order, with first order for nitrite and hydrogen ion The rate constant was measured as 1-2 M !sec . The rate constant value was independent of the presence of the spin trap Fe-MGD These data suggest that Fe-MGD does not influence the kinetic mechanism of NO production Comparision of calculated rates of the production of NO at normal physiological conditions (pH = 74, nitrite ion concentration in (issues 10 umol/kg) with the rate of reaction m conditions of ischemia (pH 5 5 after 15 min as previously shown) indicates that during the 30 min of ishemia NO would accumulate (in bound form) at levels of at least 100 nM.