Nitric Oxide as a Chain-Terminating Radical

Nitric oxide has recently been shown to react very rapidly with organic hydroperoxyl radicals (Padmaja and Huie, 1993). This rapid radical-radical addition could account for the ability of nitric oxide to inhibit lipid peroxidation (Rubbo et al., 1995). Given the relatively high lipid solubility of nitric oxide, it could readily partition into membranes, where it would be sequestered from reactive species such as superoxide and remain for longer periods to act as a chain terminator of radical-mediated lipid peroxidation. Virtually any radical species formed in or near the lipid bilayer could react with nitric oxide (e.g., tocopheryl or ascorbyl radicals) to give nitrosated intermediates or products which could in turn act as nitric oxide reservoirs. 

With respect to lipid peroxidation per se, electron abstraction from an unsaturated lipid followed by oxygen addition to the resulting carbon-centered radical gives the hydroperoxyl radical. Nitric oxide addition to the lipid hydroperoxyl radical has been shown to produce lipid ONOO s and other products that appear to rapidly decompose (Rubbo et al., 1995). 

Any determination as to whether this reaction of nitric oxide represents a protective mechanism must await further characterization of the primary and secondary reaction products as well as the mechanisms of formation and decomposition. The scavenging of superoxide by nitric oxide was considered to be an antioxidant mechanism before much was known about the product ONOO . 

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