The reaction between nitric oxide (*NO) and lipid peroxyl radicals (LOO*) has been proposed to account for the potent inhibitory properties of *NO toward lipid peroxidation processes; however, the mechanisms of this reaction, including kinetic parameters and nature of termination products, have not been defined. Here, the reaction between linoleate peroxyl radicals and *NO was examined using 2, 2'-azobis(2-amidinopropane) hydrochloride-dependent oxidation of linoleate. Addition of *NO (0.5-20 microM) to peroxidizing lipid led to cessation of oxygen uptake, which resumed at original rates when all *NO had been consumed. At high *NO concentrations (>3 microM), the time of inhibition (Tinh) of chain propagation became increasingly dependent on oxygen concentration, due to the competing reaction of oxygen with *NO. Kinetic analysis revealed that a simple radical-radical termination reaction (*NO:ROO* = 1:1) does not account for the inhibition of lipid oxidation by *NO, and at least two molecules of *NO are consumed per termination reaction. A mechanism is proposed whereby *NO first reacts with LOO* (k = 2 x 10(9) M-1 s-1) to form LOONO. Following decomposition of LOONO to LO* and *NO2, a second *NO is consumed via reaction with LO*, with the composite rate constant for this reaction being k = 7 x 10(4) M-1 s-1. At equal concentrations, greater inhibition of oxidation was observed with *NO than with alpha-tocopherol. Since *NO reacts with LOO* at an almost diffusion-limited rate, steady state concentrations of 30 nM *NO would effectively compete with endogenous alpha-tocopherol concentrations (about 20 microM) as a scavenger of LOO* in the lipid phase. This indicates that biological *NO concentrations (up to 2 microM) will significantly influence peroxidation reactions in vivo.

Nitric oxide ( • NO) and • NO-derived reactive species rapidly react with lipids during both autocatalytic and enzymatic oxidation reactions to yield nitrated derivatives that serve as cell signaling molecules. Herein we report the synthesis, purification, characterization, and bioactivity of nitrolinoleate (LNO 2). Nitroselenylation of linoleic acid yielded LNO 2 that was purified by solvent extraction, silicic acid chromatography, and reverse-phase HPLC.