Investigation of the structure of metallothioneins by proton nuclear magnetic resonance spectroscopy.

The proton nuclear magnetic resonance spectra of metallothioneins from horse, human, and sheep livers were investigated. The spectra of the metallothioneins from the three species are similar as are the two isoproteins from any one species. The spectra indicate that metallothioneins possess a well-defined tertiary structure. Zinc(II) and calcium(II) ions induce similar but not identical tertiary structures. Confirmatory evidence was obtained for the involvement of cysteine residues in metal binding, but no evidence was obtained for the involvement of any other amino acid residue in metal binding. The apoprotein thionein was found to exist essentially in a random-coil conformation with perhaps some residual segmental structure.