Ovine and bovine metallothioneins: purification, number of species, zinc content and amino acid composition.

Metallothioneins (MTs) were purified with respect to zinc from tissues of cattle and sheep which had been fed high levels of dietary zinc. These proteins were purified by gel filtration (Sephadex G-75), ion exchange chromatography (twice on DEAE Sephacel) and gel filtration again (Bio-Gel P-10). There is one major and up to three minor MT species in liver, kidney and pancreas from both sheep and cattle. The amount of zinc varies between the different species of MT. Amino acid analyses of the purified preparations revealed a cysteine content of up to 35.7% and the absence of aromatic amino acids for the major species, but the minor proteins contained less cysteine and some aromatic amino acids. The significance of MT in zinc metabolism is discussed.