Metal-binding proteins in bovine and porcine hepatic and renal tissues: isolation and characterization

Cadmium-binding proteins of single band electrophoretic purity were obtained from the hepatic and renal tissues of cows and pigs fed 2 and 10 mg of cadmium/kg of feed. Zinc, cadmium, and copper constituted a total of 4 to 5 gatom/mole of protein. Zinc and cadmium were the major metal ions of the hepatic and renal proteins, respectively. Amino acid analysis of the proteins revealed the presence of 26.1% to 28.4% cysteine and 4.3% to 5.7% histidine residues. Small amounts of hexose also were in the proteins. Molecular weights (mol wt) of the bovine and porcine hepatic proteins were 15,200 and 14,400, respectively, whereas the mol wt of their renal proteins were 7,900. Hepatic proteins seem to be in the form of two monomers chemically bound together. Large metal and cysteine concentrations and low mol wt indicated that the proteins were metallothioneins.