Investigations into the spin trapping of nitric oxide and superoxide: models to explore free radical generation by nitric oxide synthase

Abstract

Nitric oxide synthase catalyzes the oxidative metabolism of L-arginine to L-citrulline and NO˙. During cycling, this enzyme, besides generating NO˙, also secretes O2˙−. These free radicals react at diffusion controlled rates to produce ONOO−, which has been shown to decompose to give, among a variety of products, small amounts of HO˙. Thus, during oxidation of L-arginine by nitric oxide synthase, NO˙ and O2˙− will be secreted, and as a result, produce H2O2 from the dismutation of O2˙−, and ONOO− from the reaction of NO˙ and O2˙−. Hydroxyl radical can then be formed either by the reaction of H2O2 with transition metal ions or decomposition of ONOO−. Using different spin traps unique to each of these free radicals, EPR spectroscopy has been used to identify NO˙, O2˙− and HO˙.