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  • 1
    Electronic Resource
    Electronic Resource
    Electrochemical behavior of metallothioneins and related molecules. Part II: Lys-Cys-Thr-Cys-Cys-Ala thionein fragment [56-61] MT I in the presence of cadmium and/or zinc (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 670-673 
    Details
    ISSN: 1040-0397
    Keywords: Polarography ; Metallothioneins ; related molecules ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An electrochemical study, using differential pulse polarography (DPP), of a peptide Lys-Cys-Thr-Cys-Cys-Ala Thionein Fragment [56-61] MT I (FT) was performed in order to compare the behavior of metallothioneins and that of this less complex molecule, intrinsic to the metallothionein structure. The influence of different parameters, such as the solution pH and the concentration of metal elements, cadmium and zinc was investigated. Two different electrochemical systems were distinguished: in the first one, the mercury electrode itself is involved in the charge transfer steps; in this case, peaks are attributed to the oxidation of the mercury electrode in the presence of the peptide acting as a chelating agent. The second electrochemical system corresponds to the reduction of metal cations, cadmium and zinc, at a dropping mercury electrode either as free ions or complexed by the peptide. The apparent stability constants for complexes of FT with cadmium, zinc and mercury were estimated. The order of affinity is: K′HgFT ≫ K′CdFT 〉 K′ZnFT. The DPP response can be used for elucidation of the chemical forms of compounds (speciation).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140070714
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  • 2
    Electronic Resource
    Electronic Resource
    Electrochemical behavior of metallothioneins and related molecules. Part I: Lys-Cys-Thr-Cys-Cys-Ala thionein fragment [56-61] MT I (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 663-669 
    Details
    ISSN: 1040-0397
    Keywords: Polarography ; Methallothioneins ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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 × 10-5 M) and the use of a dropping mercury electrode, a diffusion controlled mechanism is suggested for the electrochemical 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 i1, ip and Ep 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.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140070713
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  • 3
    Electronic Resource
    Electronic Resource
    Electrochemical behavior of metallothioneins and related molecules. Part III: Metallothionein (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 674-680 
    Details
    ISSN: 1040-0397
    Keywords: Polarography ; Metallothionein ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical behavior 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 Cd2+ and Zn2+. 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 diflerent electrochemical species is given. DPP allows one to distinguish the chemical forms of compounds (speciation).
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140070715
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