Metallothioneins are rich in thiols, causing them to bind a number of trace metals. Metallothionein binds several Zn ions. One of few eukaryotic proteins distinguished as having a role in substantial metal detoxification. Zinc and Cadmium are tetrahedrally coordinated to cysteine residues, each metallothionein protein molecule may bind up to 7 atoms of Zn or Cd. The biosynthesis of metallothionein appeared to have increased by several-fold throughout oxidative stress to shield the cells against cytotoxicity and DNA damage. Metallothionein biosynthesis can also be induced by certain agents or conditions, for example, hormones, pharmaceuticals, alcohols, other substance treatments and many more. Metallothionein is a cytoplasmic protein, in an adult liver, it is localized mainly in the cytoplasm. In human fetus, metallothionein is localized in hepatocyte nuclei.