Metallothioneins What Are Metallothioneins? Metallothioneins are small, specialized proteins produced by the body that play a key role in regulating metals and protecting cells from toxic exposure. These proteins are rich in the amino acid cysteine, which allows them to bind tightly to metals. They are produced in several tissues throughout the body, including the liver, kidneys, intestinal lining, and brain . Their primary function is to regulate essential trace minerals suc