H-1,C-13-NMR and X-ray absorption studies of copper(I) glutathione complexes

The tripeptide glutathione (gamma-L-Glu-L-Cys-Gly, GSH) is an important intracellular reducing agent for Cu(II) and complexation agent for Cu(I). We have studied the complexation of Cu(I) to GSH in aqueous solution at a range of pH values and Cu(I):GSH molar ratios by H-1-NMR and C-13-NMR spectroscopy and X-ray absorption spectroscopy. The NMR data are consistent with formation of a complex with approximate 1:1 stoichiometry [Cu(SG)] as the major species with only thiolate sulfur of GSH binding to Cu(I). The rate of exchange of GSH with GS-Cu was determined to be 13 s(-1) at 283 K, pH 6.8. X-ray absorption spectroscopic measurements showed that Cu(I) is coordinated to 3.1+/-0.3 sulfur atoms at approximately 0.222 nm in solutions (and solids) containing GSH:Cu in 1:1 and 2:1 mol ratios. The possible structures of polymeric Cu(I)-glutathione complexes are discussed. The high thermodynamic stability of Cu(I)-S bonds in Cu(I)-glutathione complexes coupled with their kinetic lability may provide efficient and specific pathways for the transport of copper in cells.