Depressed thymidine kinase activity in zinc-deficient rat embryos.

The activity of thymidine kinase in 12-day fetuses taken from females exposed to a dietary zinc deficiency during pregnancy was significantly lower than in ad libitum (P less than .05) and restricted-intake (P less than .01) controls. Activity of the enzyme was not restored by in vitro addition of zinc at levels up to 0.075 mM but severe inhibition (approximately 50%) occurred at 0.75 mM. Enzyme activity was also severely reduced (approximately 44%) by 0.017 mM (0.96 mug/ml) of copper which raises the possibility that the reduction in thymidine kinase accompanying zinc deficiency may arise, at least in part, from an absolute or relative change in the intracellular level of copper.