Decomposition ofS-Nitrosoglutathione in the Presence of Copper Ions and Glutathione

The decomposition ofS-nitrosoglutathione (GSNO) in the presence of Cu2+and glutathione (GSH) was studied by stopped-flow/rapid-scan spectroscopy. Reduction of Cu2+by GSH and subsequent formation of a GS−∗Cu+complex occurred within 200 ms, with the amount of complex formed depending on the GSH-to-Cu2+ratio. The rate of GSNO decomposition at a fixed concentration of Cu2+increased linearly with the concentration of GSH at low GSH-to-Cu2+ratios (≤0.2), but sharply declined at higher ratios. The same pattern was observed for the rate of NO•release, measured with an NO•-sensitive electrode. GSNO decomposition and NO•release in the presence of GSH and/or Cu2+were completely inhibited by the Cu+chelator neocuproine, but unaffected by the Cu2+chelator cuprizone. Ascorbate and cysteine, which will reduce Cu2+but have little or no affinity for Cu+, also stimulated GSNO decomposition in the presence of Cu2+, but did not inhibit it at higher concentrations. It is concluded that the homolytic cleavage of GSNO is efficiently catalyzed by Cu+and that the GS−∗Cu+complex is catalytically inactive. By determining the anaerobic GSNO decomposition rates in the presence of varying concentrations of Cu+a value of 4 × 103m−1·s−1was derived for the apparent Cu+–GSNO association rate constant.