Turnover-dependent consumption of nitric oxide by 15-lipoxygenase: Modulation of nitric oxide signalling and 15-lipoxygenase activity

Abstract

The reactions of nitric oxide (*NO) during inflammatory conditions must be revealed in order to gain insight into the metabolic fates of *NO in viva In a cell line expressing physiological levels of 15lipoxygenase (LOX), rates of linoleate-stimulated *NO consumption, 7-fold higher than rates of *NO production by activated rodent macrophages, were seen. This *NO consumption did not occur in l3galactosidase-transfected controls, indicating that cellular 15-LOX has the potential to antagonize *NO signalling. Inhibition of ISlipoxygenases by *NO was previously proposed to result from ironnitrosyl complex formation between *NO and the active site ferrous iron. However, at biological *NO concentrations, no reaction with either native (Bred), or ferric lipoxygenase to form nitrosyl complexes was found. Rather, *NO consumption resulted from reaction with an enzyme-substrate Intermediate formed during the dioxygenase cycle, most probably the enzyme-bound lipid peroxyl radical, BredLOO*. During *NO consumption, partial reversible inhibition of 13(S)HPODE generation occurred, but lipid product profile was unchanged. Kinetic modelling of diene conjugation and *NO consumption rates revealed a rapid reaction of *NO with BredLOO*. Since co-generation of *NO and lS-lipoxygenase products occurs in inflammatory conditions such as atherosclerosis, interactions between these pathways will result in modulation of both *NO bioavailability and extents of production of lipid signalling mediators.