Complexation properties of the metallothionein fragment Lys-Cys-Thr-Cys-Cys-Ala [56-61] MT I with zinc using square wave voltammetry

An electrochemical study of Zn complexation with the peptide Lys-Cys-Thr-Cys-Cys-Ala thionein fragment [56-61] MT I (FT) of mouse liver was performed using square wave voltammetry in order to enable comparisons between the behaviour of Cd,Zn metallothioneins with that of this less complex molecule, intrinsic to the metallothionein structure. Optimum instrumental parameters were used in order to get the best resolution of the voltammetric peaks of both free and complexed zinc; these being low square wave frequencies and low square wave amplitudes. Complexation equilibria of the Zn-FT system as a function of metal-ligand proportion and, for a given metal-ligand ratio, as a function of pH have been studied. From the results obtained, the existence of a main complex with a stoichiometry of 1:1, in which the three thiolate groups are involved in the complexation reaction, is suggested. Another complex of a different structure and having different characteristics to the main one, probably also exists.