Isolation of a (copper,zinc)-thionein from the small intestine of neonatal rats

A Cu- and Zn-binding protein was isolated from the small intestine of 5-day-old rats whose only source of these metals was maternal milk. Elution behavior on Sephadex G-75 indicated that the molecular weight of this protein was about 9,000 daltons. Furthermore, the protein exhibited low absorbance at 280 nm, was separated into two subfractions by DEAE Sephadex chromatography and had low aromatic amino acid and high cysteine content. The protein, therefore, meets the criteria for classification as a metallothionein. Evidence suggested that the metallothionein is located primarily in the distal portion of the small intestine.