Oxidation of nitroxyl anion to nitric oxide by copper ions

1 This study made use of a nitric oxide-sensitive electrode to examine poss ible means of generating nitric oxide from nitroxyl anion (NO-) released up on the decomposition of Angeli's salt. 2 Our results show that copper ions (from CuSO4) catalyze the rapid and eff icient oxidation of nitroxyl to nitric oxide. Indeed, the concentrations of copper required to do so (0.1-100 mu M) are roughly 100-times lower than t hose required to generate equivalent amounts of nitric oxide from S-nitroso -N-acetyl-D,L-penicillamine (SNAP). 3 Experiments with ascorbate (1 mM), which reduces Cu2+ ions to Cu+, and wi th the Cu2+ chelators, EDTA and cuprizone, and the Cu+ chelator, neocuproin e, each at 1 mM, suggest that the oxidation is catalyzed by copper ions in both valency states. 4 Some compounds containing other transition metals, i.e, methaemoglobin, f erricytochrome c and Mn(III)TMPyP, were much less efficient than CuSO4 in c atalyzing the formation of nitric oxide from nitroxyl, while FeSO4, FeCl3, MnCl2, and ZnSO4 were inactive. 5 Of the copper containing enzymes examined, Cu-Zn superoxide dismutase and ceruloplasmin were weak generators of nitric oxide from nitroxyl, even at concentrations (2500 and 30 u ml(-1), respectively) vastly greater than are present endogenously. Two others, ascorbate oxidase (10 u ml(-1)) and tyro sinase (250 u ml(-1)) were inactive. 6 Our findings suggest that a copper-containing enzyme may be responsible f or the rapid oxidation of nitroxyl to nitric oxide by cells, but the identi ty of such an enzyme remains elusive.