Nitroxyl (NO-):: a substrate for superoxide dismutase

The interactions of Cu, Zn superoxide dismutase (SOD) with nitroxyl (NO-) and nitric oxide (NO), both of which are thought to be biologically significant, have been studied but remain undefined. Having previously noted that NO- can reduce Cu (II), Zn SOD aerobically, we now report that it also can do so anaerobically and that Cu, Zn SOD can catalyze the elimination of NO- in the absence of O-2 NO- acts as a reductant of ferricytochrome c anaerobically, but in the presence ofO(2), causes the oxidation of ferrocytochrome c and NADPH. Equivalent fluxes of NO-, and NO + O-2(-), were able to comparably oxidize NADPH, but the oxidation by NO + 02 was more than fivefold more sensitive to inhibition by Cu, Zn SOD than was the oxidation by NO-. Thus Cu, Zn SOD inhibited NADPH oxidation by NO- by a route independent of catalyzing the dismutation of O-2(-). Plausible mechanisms for those observations are offered and rate constants are estimated. (C) 2002 Elsevier Science (USA). All rights reserved.