Metallothioneins (MTs), containing over 33% cysteine content and lacking both aromatic amino acids and histidine, are metal binding proteins with low molecular weight (7-14 kDa). The metal ions are bound exclusively through thiolate coordination complexes which involve all 20 cysteine residues (Dunn et al. 1987). The MTs can be induced by and bind metals such as cadmium, copper, mercury, silver and zinc (Roesijadi 1992) and are capable of binding 6-7 atoms of cadmium or zinc per mole (Kagi and Schaffer 1988; Hamer 1985). The metals bound to MTs can be removed by exposure to low pH. MTs exist in vertebrates, aquatic invertebrates (Roesijadi 1992), certain bacteria (Olafson et al. 1988) and fusion yeast (Hamer et al. 1985). These proteins are found most abundant in liver, kidney, pancreas and intestine of animals, and the expression of these proteins showed a dose-response relation with the degrees of heavy metal pollution. Expression of MTs has also found to be induced by steroid hormones, interferons, certain chemicals, hepatotoxic solvent, and stresses (Kagi and Schaffer 1988). MTs have been implicated in the involvement of metabolism of copper and zinc (Cousins 1985), and in detoxification of pollutant metals, such as cadmium and mercury (Kagi and Kojima 1987). Moreover, MTs have been indicated to be an efficient scavenger for free OH(Dunn et al. 1987).