Evaluation of cadmium-metallothionein stability constants based on voltammetric measurements

A voltammetric study on the binding properties of the commercially available rabbit liver metallothionein (MT) Sigma M 7641 for cadmium ions was performed. The capacity of metallothionein to complex cadmium and the stability constants of Cd-T complex (T denotes the apoprotein or thionein molecule) have been determined from the direct titration of the defined MT concentration with the standard CdCl2 solution in 0.59 M sodium chloride medium at pH 7.9 and 2.0. At pH 7.9 the formation of the Cd-T complex has been followed measuring the specific anodic signal height of the complex. Stability constants of Cd-T have been evaluated from the experimental data using three different procedures. The calculated apparent stability constants K=(7.6+/-0.2).10(8) dm(3) mol(-1) of Cd-T complex in 0.59 M NaCl at pH 7.9 and 25 degrees C indicate that under the given experimental conditions all the three procedures are equally applicable. (C) 1998 Elsevier Science B.V.