The effects of dietary zinc on the activity of copper-requiring metalloenzymes in the rat.

It has long been known that zinc interferes with copper absorption and metabolism. In the present study, the effects of feeding rats 15, 30, 60, 120 or 240 mg Zn/kg diet on their copper status, as assessed by the activities of cupro -zinc superoxide dismutase (SOD) and cytochrome c oxidase (CCO) in heart and liver, and ceruloplasmin (Cp) in serum were determined. Although Cp activity was not related to zinc intake in a linear fashion, the number of animals with extremely low Cp activity increased with increasing zinc. The level of zinc at which 50% of animals would have abnormally low Cp activity was calculated to be 125-129 ppm zinc. Liver SOD and heart CCO activities decreased linearly with increasing zinc and were significantly reduced compared to controls at 120 and 240 ppm Zn, respectively. Thus, animals fed zinc at levels as low as four times the AIN recommended concentration showed biochemical signs of copper deficiency.