Isolation and characterization of a hepatic metallothionein from mice

Mice were given cadmium chloride orally for 18 weeks, after which they were given two subcutaneous injections of cadmium chloride. Cadmium-and zinc-containing proteins were obtained from livers by ultracentrifugation, Sephadex chromatography and isoelectric focusing. Metallothionein with apI of 4.2 at 8 degrees C was separated from other proteins (possibly including other forms of metallothionein) by the isoelectric procedure. The metallothionein with pI = 4.2 had a high E250, reflecting abundant Cd-SH bonds, in accord with amino acid analysis, which gave a cysteine content of 34.6 residues % and showed an absence of aromatic amino acids. These results indicated a very high purity of the form of metallothionein isolated after isoelectric focusing.