Mechanism of S-nitrosothiol formation and degradation mediated by copper ions.

Experimental evidence is presented supporting a mechanism of S-nitrosothiol formation and degradation mediated by copper ions using bovine serum albumin, human hemoglobin and glutathione as models. We found that Cu(2+), but not Fe(3+), induces in the presence of NO a fast S-nitrosation of bovine serum albumin and human hemoglobin, and the reaction is prevented by thiol blocking reagents. During the reaction, Cu(+) is accumulated and accounts for destabilization of the S-nitrosothiol formed. In contrast, glutathione rapidly dimerizes in the presence of Cu(2+), the reaction competing with S-nitrosation and therefore preventing the formation of S-nitrosoglutathione. We have combined the presented role of Cu(2+) in S-nitrosothiol formation with the known destabilizing effect of Cu(+), providing a unique simple picture where the redox state of copper determines either the NO release from S-nitrosothiols or the NO scavenging by thiol groups. The reactions described are fast, efficient, and may occur at micromolar concentration of all reactants. We propose that the mechanism presented may provide a general method for in vitro S-nitrosation.