engleski

Electrochemical study on Cd binding to metallothioneins isolated from the mussel, Mytilus galloprovincialis

Voltammetric studies on the binding properties of the purified MT fractions isolated from mussel (Mytilus galloprovincialis) digestive gland for cadmium ions were performed. The capacity of MT to complex cadmium and the stability constants of Cd- MT complex have been determined from the direct titration of MT with cadmium ions in 0.59 mol dm-3 NaCl medium at pH=7.9. Comparing cadmium binding properties of the two studied isoforms of mussel MT denoted as MT10(III) and MT10(IV), it appears that they are distinctly different. In the presence of two different MT isoforms voltammetric determination of cadmium results in specific anodic signals which are observed at Ep= -0, 67V and at Ep= -0, 80V (vs. Ag/AgCl electrode) for isoform MT10(III), and isoform MT10(IV) respectively, indicating the existence of two different Cd-MT complexes. It is in agreement with the difference in their calculated apparent stability constants (K=9?109 dm3 mol-1 for MT10(III) and K=1.4?1010 dm3 mol-1 and K=2.0?1010 dm3 mol-1 for MT10(IV)). The saturation of the two MT10 fractions occurs at different Cd(II) concentrations, and the capacity of MT10(IV) to bind cadmium ions is 2.5 times greater than the capacity of MT10(III). The applied electrochemical technique, and method for the experimental data assessment presented in this study are suitable for physico-chemical characterization of metallothioneins as the proteins responsible for binding of toxic metals on cellular level. Using the voltammetric method time dependent changes of the three-dimensional structure of the MT molecule were observed.

metallothioneins ; isoforms ; cadmium binding ; mytilus galloprovincialis ; voltammetry

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