title: The pharmacological mechanism of angiotensin-converting enzyme inhibition by green tea, Rooibos and enalaprilat - a study on enzyme kinetics.
abstract: 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 V(max)  = 3.73 µM and K(m)  = 0.71 µM for green tea, of V(max)  = 6.76 µM and K(m)  = 0.78 µM for Rooibos, of V(max)  = 12.54 µM and K(m)  = 2.77 µM for enalaprilat, and of V(max)  = 51.33 µM and K(m)  = 9.22 µM 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.
authors.affiliation: Department of Medical and Health Sciences, Division of Drug Research/Pharmacology, Faculty of Health Sciences, Linköping University, Sweden. Ingrid.persson@liu.se
authors.forename: Ingrid A-L
authors.initials: IA
authors.lastname: Persson
mesh_terms: D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology*; D036903:Aspalathus / Q000737:chemistry*; D028241:Camellia sinensis / Q000737:chemistry*; D002712:Chlorides / Q000494:pharmacology; D015773:Enalaprilat / Q000494:pharmacology*; D057075:Enzyme Assays; D006801:Humans; D007700:Kinetics; D016014:Linear Models; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism; D021281:Quantitative Structure-Activity Relationship; D044967:Serum / Q000737:chemistry / Q000201:enzymology; D013053:Spectrophotometry; D017967:Zinc Compounds / Q000494:pharmacology
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D002712:Chlorides; D017967:Zinc Compounds; C016837:zinc chloride; D007703:Peptidyl-Dipeptidase A; D015773:Enalaprilat