Effects of Oolong Tea Polyphenols, EGCG, and EGCG3Me on Pancreatic α-Amylase Activity in Vitro

In order to investigate the inhibitory effects and possible mechanisms of Oolong tea polyphenols, (-)-epigallocatechin gallate (EGCG) and (-)-epigallocatechin 3-O-(3-O-methyl) gallate (EGCG3 '' Me) on pancreatic alpha-amylase, the inhibition, enzyme kinetics, ultraviolet (UV) absorption spectrum and fluorescence spectrum of alpha-amylase were investigated. The results showed that Oolong tea polyphenols, EGCG, and EGCG3 '' Me all exhibited inhibitory effects against alpha-amylase, and their half inhibitory concentration (IC50) values were 0.375, 0.350, and 0.572 mg/mL, respectively. The results of Lineweaver-Burk double reciprocal plot indicated that the inhibitory types of Oolong tea polyphenols and EGCG were competitive, whereas EGCG3 '' Me was in a noncompetitive pattern. Oolong tea polyphenols, EGCG, and EGCG3 '' Me all induced red-shift of UV absorbance and quenching of fluorescence of alpha-amylase, suggesting possible changes in the conformation of alpha-amylase. The differences of inhibitory effects and inhibition types for EGCG and EGCG3 '' Me might be due to their structural difference (the hydroxyl group at C-3 in D ring of EGCG substituted by methoxy group, forming EGCG3 '' Me).