The Pharmacological Mechanism of Angiotensin-converting Enzyme Inhibition by Green Tea, Rooibos and Enalaprilat - A Study on Enzyme Kinetics

Green tea (Camellia sinensis L.) and Rooibos (Aspalathus linearis Dahlg.) inhibit angiotensin‐converting enzyme (ACE) in vitro and in vivo. The ACE inhibitor enalaprilat has been described previously as a competitive inhibitor and sometimes as a non‐competitive inhibitor. The aim of this study was to investigate the pharmacological mechanism of ACE inhibition of green tea and Rooibos by enzyme kinetics, and to compare this with enalaprilat. A Michaelis–Menten kinetics and Lineweaver–Burk graph showed mean values of Vmax = 3.73 µ m and Km = 0.71 µ m for green tea, of Vmax = 6.76 µ m and Km = 0.78 µ m for Rooibos, of Vmax = 12.54 µ m and Km = 2.77 µ m for enalaprilat, and of Vmax = 51.33 µ m and Km = 9.22 µ m for the PBS control. Incubating serum with green tea or Rooibos saturated with zinc chloride did not change the inhibitory effect. Enalaprilat preincubated with zinc chloride showed a decrease in the inhibitory effect. In conclusion, green tea, Rooibos and enalaprilat seem to inhibit ACE activity using a mixed inhibitor mechanism. Copyright © 2011 John Wiley & Sons, Ltd.