Effects of dietary zinc deprivation on the activity of angiotensin-converting enzyme in serum of rats and guinea pigs.

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidyldipeptide hydrolase found in blood and in the endothelium of many tissues. This study was designed to determine the effects of dietary zinc deprivation in rats and guinea pigs on ACE activity in serum. Rats were fed zinc-deficient (less than 1 mg/kg) or zinc-adequate (25 mg/kg) diets for 3 d. Guinea pigs were fed zinc-deficient (less than 1 mg/kg) or zinc-adequate (100 mg/kg) diets for 3 wk. The plasma zinc concentration in the zinc-deprived rats was 26% and that of the deprived guinea pigs 35% of the control values. When serum was diluted by one-half in the assay medium, the respective ACE activities were 42 and 59% of controls. In spite of decreased ACE activity there were no differences in plasma angiotensin II levels in either species or in bradykinin levels in the rat. To determine the effect of zinc on the kinetics of serum ACE, rat serum was treated to remove low-molecular-weight components and diluted 30-fold in an assay medium that contained a final zinc concentration of 0.68 microM. Supplemental zinc (total, 24 microM) increased both Vmax and Km. EDTA inhibited the enzyme activity, and the inhibition was totally reversible by zinc. Copper at 30 microM had no effect on ACE activity. The results of this study show that ACE activity in serum of rats and guinea pigs is highly sensitive to the dietary intake of zinc and suggest that metabolism of the vasoactive hormones, angiotensin II and bradykinin, might be affected in vivo.