Reaction of Nitric Oxide with ONOO

ONOO formation in vivo involves a competition between nitric oxide and SOD for the available superoxide. The fraction of total NO which ends up as ONOO is always lower than the remaining fraction of free NO. Thus, nitric oxide would be in molar excess over ONOO under most 

SCHEME 4 Proposed reaction mechanisms for peroxynitrous acid (ONOOH) attack on phenol based on product yield and distribution. 

The reaction between ONOO and nitric oxide in phosphate buffer at physiological pH does not consume or produce oxygen, nor is nitrous oxide (N2O) produced (Crow and Beckman, unpublished observations). The relatively high concentrations of nitric oxide used for product analysis experiments resulted in the production of both nitrite and nitrate, as did decomposition of ONOO alone NO2 and NOj production were merely additive 

FIGURE 2 Peroxynitrite (ONOO )-induced loss of nitric oxide signal. A saturated aqueous solution (0.5 jul) of nitric oxide (1.9 mM) was added to a stirred 1-ml solution of 0.1 M potassium phosphate (pH 7.4) at 37°C. ONOO was added at the times indicated. ONOO (40 /U.M) was allowed to decompose at pH 7.4 for 1 min prior to addition. Nitric oxide diffused through a hollow fiber immersed in the solution and was carried to a chemiluminescence detector by a helium flow. The dead time for measurement of nitric oxide added to the solution is approximately 1 sec. 

Regardless of the exact reaction mechanism, these results suggest that the biological half-life of nitric oxide per se would be shortened by ONOO . On the other hand, if the net effect of the ONOO /nitric oxide reaction was to increase the yield of nitrosothiol, it is conceivable that the biological effects of nitric oxide could be prolonged. 

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