Generation of nitric oxide from S-nitrosothiols using protein-bound Cu2+ sources

Background: We have recently shown that S-nitrosothiols (RSNOs) decompose in aqueous buffer to give nitric oxide, an important signalling molecule, and the corresponding disulphides. This occurs by reaction with Cu+ generated from CU2+ (supplied as hydrated CU2+) by thiolate reduction. To establish whether these reactions are feasible in vivo, we set out to determine whether CU2+ bound to an amino acid, a tripeptide or to human serum albumin (HSA) could serve as a Cu+ source for generation of NO from S-nitrosothiols. Results: Experiments with CU2+ bound to the tripeptide Gly-Gly-His or to two histidine molecules or to HSA showed that Cu+ was released (and trapped with neocuproine) when the copper source was treated with a thiol at pH 7.4. RSNO decomposition was achieved with all three copper sources, although not as rapidly as with added hydrated CU2+. Decomposition was also catalyzed by ceruloplasmin. Conclusions: These results show clearly that amino-acid- and protein-bound CU2+ can be reduced by thiolate ion to Cu+, which will generate NO from RSNO species, thus providing a realistic model for these reactions in vivo.