Electrochemical study of metallothioneins using cyclic voltammetry

The electrochemical study of two different metallothioneins (MT) from rabbit liver, one of them containing almost only cadmium and the other containing almost only zinc in the molecule, was performed by cyclic voltammetry using a hanging mercury drop electrode. The influence of several parameters, i.e. scan range, number of cycles, quiet time, scan rates and concentration was investigated in order to elucidate the diffusion-adsorption process. The variation of the initial potential, allowing or avoiding the oxidation of the mercury electrode in the presence of thiol groups of the MT complexed by cations, modifies the concentration of compounds near the electrode surface and consequently the features of the voltammograms, particularly in the case of the zinc-metallothionein. In fact, the behaviour of both cadmium-MT and zinc-MT as a function of the parameters studied is similar, but not identical. Peaks corresponding to the electrochemical system of the cadmium complexes behave as expected for an electrochemical reaction where the product is adsorbed weakly. The variation of the reduction potential for the zinc complexes is more dependent on the experimental conditions, which are determining whether the adsorption phenomenon and the accumulation process are or are not important. In the first cycle and at low concentration of compounds the electrochemical systems are mainly diffusion controlled. (C) 1998 Elsevier Science S.A. All rights reserved.