Contribution to the study of complexing properties of Zn-metallothioneins by CZE-DAD

The complexing properties of the sub-isoforms of several mammalian Zn-conta ining metallothioneins (ZnMT) from different origins (rat, rabbit and human foetal livers) have been investigated by capillary zone electrophoresis co upled to diode array detection (CZE-DAD). MTs were submitted to three diffe rent experiments: gradual additions of Cd to MT at PH 8.0, variation of the pH and addition of Cd followed by a variation of the pH. On the whole ther e seems to he no displacement of the zinc originally present in the MT, but incorporation of Cd in the molecule in order to reach saturation. Furtherm ore, the pH variations allow one to conclude a certain reversibility of the system. All these results confirm those previously obtained by differentia l pulse polarography (DPP). The procedure used in this work shows that the sub-isoforms of an MT may exhibit variable complexing properties. This is p articularly well illustrated in the case of rat liver MT-2. Much likely the re are different mixed complexes of Cd and Zn in each sub-isoform, forming various metalloforms. This work illustrates a different and original use of CZE-DAD for studying the complexing properties of metal-binding proteins. (C) 2000 Elsevier Science B.V. All rights reserved.