title: Inhibition of angiotensin converting enzyme (ACE) activity by polyphenols from tea (Camellia sinensis) and links to processing method.
abstract: The focus of this study was to investigate Angiotensin Converting Enzyme (ACE) inhibiting activity across 34 teas (Camellia sinensis) produced by 5 different processing methods including green (GT), oolong (OT), white (WT), black (BT) and dark (DT) teas. In vitro ACE inhibitory activity was affected by the tea processing method with IC(50) values for ACE inhibition: green < oolong < white < black < dark teas. Substrate-dependence of the reaction kinetics was studied for GT and BT polyphenolic size fractions either < or > 3 kDa and also Green Tea Polyphenolic Isolate (GTPI), and revealed that enzyme velocity curves fitted allosteric, not Michaelis-Menten, relationships. Inhibition was weakly dependent on substrate concentration for GT fraction >3 kDa and independent of substrate concentration for all other GT and BT size fractions and GTPI. Furthermore, evidence for direct inactivation of ACE by GTPI was demonstrated. Overall, the results suggest that tea polyphenolics exert a mixed mode of in vitro inhibition of ACE, mostly of a kinetically uncompetitive type. The results are discussed in the context of in vivo and epidemiological evidence for regulation of blood pressure by tea consumption.
authors.affiliation: CSIRO Preventative Health Flagship, CSIRO Food and Nutritional Sciences, 671 Sneydes Road, Private Bag 16, Werribee, Victoria 3030, Australia.
authors.forename: Junjie
authors.initials: J
authors.lastname: Dong
authors.forename: Xinqing
authors.initials: X
authors.lastname: Xu
authors.forename: Yuerong
authors.initials: Y
authors.lastname: Liang
authors.forename: Richard
authors.initials: R
authors.lastname: Head
authors.forename: Louise
authors.initials: L
authors.lastname: Bennett
mesh_terms: D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology*; D000975:Antioxidants / Q000494:pharmacology*; D028241:Camellia sinensis / Q000737:chemistry*; D005511:Food Handling / Q000379:methods; D020128:Inhibitory Concentration 50; D007700:Kinetics; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism*; D018515:Plant Leaves / Q000737:chemistry; D059808:Polyphenols / Q000302:isolation & purification / Q000494:pharmacology*; D013662:Tea / Q000737:chemistry*
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D000975:Antioxidants; D059808:Polyphenols; D013662:Tea; D007703:Peptidyl-Dipeptidase A