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Effects of Dietary Zinc Deprivation on the Activity of Angiotensin-Converting Enzyme in Serum of Rats and Guinea Pigs^1,2,

Department of Biochemistry, 322 Chemistry Building, University of Missouri, Columbia, MO 65211

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidyl-dipeptide 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 (<1 mg/kg) or zinc-adequate (25 mg/kg) diets for 3 d. Guinea pigs were fed zinc-deficient (<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 µM. Supplemental zinc (total, 24 µM) increased both V_max and K_m. EDTA inhibited the enzyme activity, and the inhibition was totally reversible by zinc. Copper at 30 µM 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.

KEY WORDS: • zinc deficiency • angiotensin-converting enzyme • plasma zinc • copper • angiotensin II • bradykinin • rats • guinea pigs

¹ This work was supported in part by the Missouri Agricultural Experiment Station, Journal Series No. 9844 and by the U.S. Department of Health and Human Services, Grant No. HL11614.

² A preliminary report of these data was presented at the 1985 Federation of the American Societies for Experimental Biology meetings in Anaheim, CA. Roeves, P. G. & O'Dell, B. L. (1985) Effect of Zn deficiency on the activity of angiotensin converting enzyme in serum of rats and guinea pigs. Fed. Proc. 44, 542 (abs. 767).

Manuscript received 15 April 1985. Revision accepted 24 September 1985.