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The electrochemical behaviour of Cd-Zn thionein from rabbit liver and horse kidney with respect to pH of the solution at the dropping mercury electrode was studied, using differential pulse polarography (DPP). At pH 7.5 three well-defined peaks were observed at a potential different from the potentials corresponding to pure Cd(2+) and Zn(2+). Two different electrochemical systems are involved: the oxidation of the mercury electrode in the presence of thiol groups contained in the metallothionein and the reduction of either free (pH <4) or complexed (pH >6) metal ions. The apparent acid-base dissociation constant of metallothionein was estimated. The apparent stability constants of the complexes CdT, ZnT and HgT were estimated at different pH values. Cadmium forms at least two complexes with thionein exhibiting different stabilities and probably different structures. Modifications in the polarograms with the addition of Cd, Zn and the peptidic fragment [56-61] MT I, a molecule intrinsic to the metallothionein structure, were studied. A diagram showing the oxido-reduction potentials corresponding to twelve different electrochemical species is given. DPP allows the chemical forms of compounds (speciation) to be distinguished.

Additional information

Authors: MUÑOZ A, JRC Geel (BE);RODRIGUEZ A, University of Wisconsin, Department of Chemistry, Milwaukee (US)
Bibliographic Reference: Article: Electroanalysis, Vol. 7 (1995) No. 7, pp. 674-680
Record Number: 199511418 / Last updated on: 1995-11-03
Original language: en
Available languages: en
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