Voltammetry on mercury and carbon electrodes as a tool for studies of metallothionein interactions with metal ions

Rabbit liver Cd-metallothionein (CdMT) and Cd-complex of synthetically prep ared pentapeptide (gamma-Glu-Cys)(2)-Gly were studied as examples of animal and plant metallothioneins, Using hanging mercury electrode, cathodic stri pping voltammetry after adsorptive accumulation of the Cd(II)-SR complex at different potentials, is suitable for estimating changes occurring in meta l coordination due to the presence of metal ions such as Zn2+, Cu2+ Hg2+ or excessive Cd2+. Conditions under which similar behaviour can be observed f or both CdMT and Cd-pentapeptide complex are specified. On carbon electrode s, detailed study of reduction processes of Cd(II)-SR complexes is prevente d by occurrence of a large catalytic current; oxidation processes are more suitable for study at these electrodes. Carbon composite paste electrode (1 0% SiO2) allows deposition of Cd(II)-SR complex during its reduction, as wa s demonstrated with Cd-cysteine, CdMT or Cd-pentapeptide complex. After dep osition, oxidation peak of the uncomplexed Cd2+ ions and one or two oxidati on peaks corresponding to a formation of the RS-Cd(II) complex are observed . Also, similarly as on Hg electrode, it was observed that excessive Cd2+ o r Zn2+ ions influence oxidation peaks of the RS-Cd(II) complex formation. C ombination of measurements on mercury electrode and composite paste electro de is recommended for studies of metallothionein interactions with metal io ns or other metal complexes.