Studies on the Synthesis and Metabolism of Zinc-thionein in Rats

Abstract

The objectives of this investigation were to study the role of zinc-thionein in the metabolism of excessive amounts of zinc and the re-utilization of zinc bound to this protein. Rats were injected ip with 5 mg Zn/kg body weight as zinc chloride for 5 days to induce the synthesis of zinc-thionein. Proteins with molecular weight of 10,000 with high affinity for zinc were synthesized in rat liver and intestine. These proteins were heat stable. Large scale isolation of this protein from rat liver was achieved by a simple method consisting of a heating step and sephadex gel fractionation. Intravenous injection of isolated ⁶⁵Zn-thionein to rats resulted in similar organ distribution of zinc as that after ⁶⁵ZnCl₂ injection. Gel filtration experiments with liver supernatant from rats injected with ⁶⁵Zn-thionein showed that a major portion of ⁶⁵Zn was transfered to other protein fractions and was re-utilized similar to inorganic salts of zinc. Morphological studies showed no toxic effects after injection of zinc-thionein. These results show that zinc-thionein is metabolically active and non-toxic.