Electrochemical characterization of metallothionein metal-mercaptide complexes: Application of cyclic voltammetry to investigation of metalloproteins

Abstract

Electrochemical studies of metalloproteins have considerable potential in the investigation of metal-complex structures. Due to a lack of information on the precise nature of the results obtained however, application of electrochemistry has been largely neglected by protein chemists. This report discusses the cyclic dc voltammetry of a selection of proteins with particular reference to metallothioneins (MTs) and interpretation of waves associated with MT metal-protein complexes. Comparison of voltammograms of proteins in the presence and absence of added metal, together with scans of a selection of native MTs, has allowed for the designation of waves associated with specific metal complexes. The contrast in electrochemical activity between proteins free of thiols or disulfide bonds with those rich in these functionalities was also shown. Evidence from saturation plots, peak current versus scan rate plots and detergent competition studies with MTs, indicated that the major electrochemical process at the mercury electrode was adsorption rather than diffusion controlled. Characterization of native MT metal speciation and assessment of the fidelity of metal reconstitution of laboratory produced thionein was readily feasible using cyclic voltammetry and nanomole quantities of material.