Polythiol binding to biologically relevant metal ions

Abstract

The coordination properties of three peptides with CXXC motif: Ac-GCASCDNCRACKK-NH₂, Ac-GCASCDNCRAAKK-NH₂ and Ac-GCASCDNARAAKK-NH₂ as donors of four, three and two thiol ligands for Ni²⁺,Cd²⁺, Zn²⁺ and Bi³⁺ were studied by potentiometric titrations, UV-Vis and CD spectra measurements. Since the stability of the complexes is closely connected with the amount of the metal- bound cysteine sulfurs, competition plots of the complexes of peptides with 2, 3 and 4 cysteines further prove the involvement of all thiols in the metal ion binding. Furthermore, the sulfur- bound zinc complexes appear to be much more stable than the sulfur- bound nickel ones. The stabilities of the studied complexes decreases in the series Bi³⁺ ≫ Cd²⁺ > Zn²⁺ > Ni²⁺.