ELECTROCHEMICAL-BEHAVIOR OF METALLOTHIONEINS AND RELATED MOLECULES .1. LYS-CYS-THR-CYS-CYS-ALA THIONEIN FRAGMENT [56-61] MT-I

In order to obtain a better understanding of the electrochemical behavior of the Metallothionein (MT), the peptidic fragment Lys-Cys-Thr-Cys-Cys-Ala [56-61] MT I (FT) compound constitutive of the proteic structure has been studied. The elucidation of the electrochemical mechanism at the electrode could be reached from comparison with other mechanisms proposed for similar molecules. This study stems from a more complete work. Under our experimental conditions, with a low concentration of the substance ( < 5 x 10(-5) M) and the use of a dropping mercury electrode, a diffusion controlled mechanism is suggested for the electrochemicel behavior of FT. In this case the mercury electrode itself is involved in the charge transfer step and the polarographic response is attributed to the oxidation of the mercury electrode in the presence of the chelating agent FT. This hypothesis was supported by the lack of modification of the electrocapillary curves in the presence of low concentration of FT in relation to those obtained with the supporting electrolyte alone and by the linear relationship between the polarographic intensity and the concentration at a low concentration of FT. The influence of the pH of the solution on the behavior of FT was investigated using DC and DPP methods. The variation of i(i), i(p) and E(p) with pH was determined. From these results the apparent acid-base dissociation constant of the FT was evaluated, corresponding to the dissociation of protons from the thiol groups. Likewise the apparent stability constants of the Hg-FT were estimated as a function of the pH. It was assumed that the main complex of Hg-FT possessed a stoichiometry of 1:1 but it is probable that two or more different complexes coexisted.