Potentiometric and spectroscopic studies on the copper(ii) complexes of rat amylin fragments. The anchoring ability of specific non-coordinating side chains

Abstract

Copper(II) complexes of peptides modelling the sequence of the 17–22 residues of rat amylin have been studied by potentiometric, UV-Vis, CD and ESR spectroscopic methods. The peptides were synthesized in N-terminally free forms, NH₂-VRSSNN-NH₂, NH₂-VRSSAA-NH₂, NH₂-VRAANN-NH₂, NH₂-VRSS-NH₂, NH₂-SSNN-NH₂, NH₂-SSNA-NH₂ and NH₂-AANN-NH₂, providing a possibility for the comparison of the metal binding abilities of the amino terminus and the –SSNN– domain. The amino terminus was the primary ligating site in all cases and the formation of only mononuclear complexes was obtained for the tetrapeptides. The thermodynamic stability of the (NH₂, N⁻, N⁻) coordinated complexes was, however, enhanced by the asparaginyl moiety in the case of NH₂-SSNN-NH₂, NH₂-SSNA-NH₂ and NH₂-AANN-NH₂. Among the hexapeptides the formation of dinuclear complexes was characteristic for NH₂-VRSSNN-NH₂ demonstrating the anchoring ability of the –SSNN– (SerSerAsnAsn) domain. The complexes of the heptapeptide NH₂-GGHSSNN-NH₂ were also studied and the data supported the above mentioned anchoring ability of the –SSNN– site.