Mechanism of superoxide dismutase/H2O2-mediated nitric oxide release from S-nitrosoglutathione role of glutamate

S-Nitrosoglutathione (GSNO), a physiologically relevant nitric oxide ((NO)- N-.) donor, exhibits antioxidant, anti-ischemic, and antiplatelet propertie s. The exact mechanism of (NO)-N-. release from GSNO in biological systems has not been determined. Both copper ions and copper-containing enzymes hav e been shown to catalyze (NO)-N-. release from GSNO. In this study we obser ved that copper-zinc superoxide dismutase (Cu,ZnSOD) in the presence of H2O 2 caused a rapid decomposition of GSNO, forming oxidized glutathione (GSSG) and (NO)-N-.. The cupric ions (Cu2+) released from Cu,ZnSOD were bound to the glutamate moiety of GSNO, yielding a 2:1 (GSNO)(2)Cu2+ complex. Strong chelators of cupric ions, such as histidine and diethylenetriaminepentaacet ic acid, inhibited the formation of (GSNO)(2)Cu2+ complex, GSSG, and (NO)-N -.. GSSG alone inhibited Cu2+-induced decomposition of GSNO. This effect is attributed to complexation of copper by GSSG. We conclude that binding of copper to GSNO is obligatory for (NO)-N-. release from GSNO; however, the r ate of this reaction was considerably slowed due to binding of CU2+ by GSSG . The glutamate moiety in GSNO and GSSG controls copper-catalyzed (NO)-N-. release from GSNO. Cu,ZnSOD and H2O2 enhanced peroxidation of unsaturated l ipid that was inhibited by GSNO. The antioxidant function of GSNO is relate d to the sequestering of copper by GSNO and its ability to slowly release ( NO)-N-.. Implications of these findings are discussed in relation to GSNO-i nduced cardioprotection and to neuropathological processes. (C) 1999 Academ ic Press.