An experimental study of the effect of zinc on the activity of angiotensin converting enzyme in serum.

The activity in serum of zinc-dependent angiotensin converting enzyme (ACE), is measured to aid in diagnosis and monitor treatment of certain diseases. This report shows the effect of dietary zinc deprivation on ACE activity in the serum of rats. The mean (and SE) of the zinc concentration (mumol/L) in serum was 3.5 (0.3) in rats deprived of dietary zinc for four days, 16.3 (0.2) in control rats, and 19.8 (0.9) in rats deprived of zinc for four days, then repleted with zinc for 12 h. The respective mean (and SE) of ACE activities (nmol/mL per min) in serum were 390 (15), 543 (13), and 545 (20). Serum ACE activity was restored also by adding zinc to the assay mixture in vitro. The Vmax for ACE was 1.4 times greater when serum was diluted 40-fold as compared with twofold dilution. There was a small effect on the Km for the substrate, but the Km for zinc was decreased by 22-fold when serum was diluted 40-fold. The Vmax under these conditions was decreased by only 9%.