Printed in Great Britain Effect of Zinc Status of Rats on the Synthesis and Degradation of Copper - hduced Metailothioneins

Injection ofZn2+-adequate and Zn2+-deficient rats with Cu2+ stimulated the incorporation of L-[35S]cysteine into a low-molecular-weight Cu2+-binding protein in both liver and kidney. No significant incorporation of L-[4,5-3H]leucine into this protein occurred, confirming the previous claim that it was metallothionein and not some other leucine-rich protein. The half-life of the protein was found to be 16.9 ± 1.0 (s.E.)h in the liver of Zn2+adequate rats but only 12.3 ±0.5h in Zn2+-deficient animals. The degradation rate of the metallothionein was similar to the rate of disappearance of Cu2+ and Zn2+ from the protein, indicating that the release of metal from the protein and its catabolism occurred simultaneously. There was no significant difference in the half-lives of the hepatic or renal copper-thioneins in Zn2+-adequate rats.