Abstract
Metallothioneins are low molecular weight proteins (6–7000) characterized by extremely high sulfur and metal content. These proteins, which mostly bind Zn 2+, Cd 2+ and Cu +, appear to play a major role in zinc and copper metabolism and in heavy metal detoxification. All 20 cysteine residues out of a total of 61 amino acids are involved in the binding of a total of seven Group 2B metals via thiolate linkages. Since the threedimensional structure is still unknown, all structural information comes exclusively from spectroscopic studies. Proof for a T d type of symmetry with four thiolate ligands was obtained from Co(II), γ-PAC and EXAFS spectroscopic studies. Furthermore, 113Cd NMR as well as Co(II)-ESR and magnetic susceptibility measurements showed that metal-thiolate complexes are organized in clusters for which an adamantane-related structure was proposed. Recent hydrodynamic measurements, as well as studies on the temperature dependence of 113Cd NMR spectra, suggest that metallothioneins have a flexible structure.
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