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Cd,Zn metallothioneins (MT) of human origin have been studied by differential pulse polarography in the HEPES-phosphate buffer. The MTs were isolated at the biochemistry laboratory of the Catholic University of Leuven. They contain either cadmium or zinc or a mixture of both cations. Their origins are fetal liver or adult kidney. The total metal content, cadmium and zinc, have been determined by Electrothermal Atomic Absorption Spectrometry.

The electrochemical behaviour of these MTs with respect to the pH, from neutral to basic and, then, from basic to acid solutions has been investigated in order to verify the reversibility of the complexation equilibrium. The human MTs behave analogously to the other mammalian MTs obtained from Sigma Co, which were previously studied under the same experimental conditions. Two polarographic peaks, labelled CdT and CdT' and attributed to the reduction of cadmium complexed by the thioneins, have been detected; these results comparing well with those obtained in the case of the Sigma MTs. However, the stability of human MTs with respect to the changes in pH is lower than that of Sigma MTs and it depends on their origin as well as on the sample storage conditions. On going to acid pH, the response attributed to the electrochemical reaction of thiol groups decreases until its total disappearance. When the pH changes again from acid to neutral the polarogramme is different to the initial one, indicating that the human MTs have been denatured and, in several cases, their complexation properties are lost.

The addition of cadmium and zinc to Cd, Zn MT has been performed. At neutral pH the addition of zinc provokes the shift of the peak potential corresponding to the cadmium initially contained in the Cd, Zn thioneins. This fact has previously been attributed to a modification in the metallothionein structure and, consequently, to a change in the properties of the cadmium-thionein complex(es). s).

Additional information

Authors: RUIZ C, JRC Geel (BE);RODRIGUEZ A R, JRC Geel (BE)
Bibliographic Reference: Paper presented: 6th European Conference on Electroanalysis ESEAC 96, Durham (GB) March 25-29, 1996
Availability: Available from (1) as Paper EN 39604 ORA
Record Number: 199611118 / Last updated on: 1996-10-28
Original language: en
Available languages: en