Voltammetric Methods in Metallothionein Research

The application of voltammetric methods using different rates of polarisation on HMDE reveal inert or labile behaviour of Cd- or Zn- complexes in the presence of excessive cadmium or zinc ions in solution. This phenomenon was demonstrated first on the simplest phytochelatin – complex of peptide (γ-Glu-Cys)(2) Gly with cadmium, later on rabbit liver metallothioneins – Cd(7) MT in the presence of cadmium and Cd(5) Zn(2) MT in the presence of zinc. Voltammetric methods can distinguish between labile and inert complexes present simultaneously and therefore could elucidate their role in reactions of metal ion transfer. Another method using different rates of polarisation – elimination voltammetry with linear scan – proved that S-tetracoordinated complexes of Cd(II) or Zn(II) in the above-mentioned metallothioneins on HMDE are reduced in the adsorbed state. This implies the possibility of increasing the sensitivity of identification or determination of the above complexes. On carbon composite electrode, similar behaviour of Cd-complexes as on HMDE was observed using differential pulse voltammetry.