Monitoring of the metal displacement from the recombinant mouse liver metallothionein Zn7-complex by capillary zone electrophoresis with electrospray MS detection

A solution of a Zn-complex of recombinant mouse MT-1 isoform (Zn7–MT-1) was prepared and titrated with Cd2+ ions. A method based on the coupling of capillary zone electrophoresis (CZE) with electrospray MS detection was developed for the analysis of the stoichiometry of the species formed during the titration. The method offered the possibility of the on-line removal of up to 100 mM Tris or phosphate buffer solutions that would otherwise suppress the electrospray signal. By allowing the determination of the metal stoichiometry of the complex species present in solution the method was shown to be complementary to circular dichroism and UV–VIS spectrophotometry conventionally used for similar studies. The titration of the Zn7–MT complex with Cd(II) showed the sequential displacement of the Zn by Cd. The unusually high stability of the Cd6Zn1–MT species was observed which suggests a structural role of the remaining Zn(II) ion.