Electrochemical study of the binding properties of a metallothionein I related peptide with cadmium or/and zinc

An electrochemical study, using differential pulse polarography, of the binding properties of the peptide Lys-Cys-Thr-Cys-Cys-Ala Thionein Fragment [56-61] MT I (FT) with cadmium and zinc was performed. This molecule, intrinsic to the metallothionein structure, was chosen as a model of the Cd, Zn Metallothioneins ion exchange and binding properties. The influence of the addition of metal ions, cadmium and/or zinc was studied with different ratios of complexing ligand/metallic cations, FT/M(II). It is assumed that the main complex M(II)-FT possesses a stoichiometry of 1:1, but probably two or more complexes co-exist depending on the FT/M ratios. The equilibrium M + FT reversible arrow MFT concerning the complexation equilibrium of formation and dissociation was investigated as a function of pH, going from acid to basic solution and vice versa in different mixtures: Cd:FT, Zn:FT and Cd:Zn:FT. The apparent stability constants of the complexes Cd-FT, Zn-FT were estimated at different pH values.