The Mechanisms of Alpha-Amylase Inhibition by Flavan-3-Ols and the Possible Impacts of Drinking Green Tea on Starch Digestion
Abstract
Many studies have shown that flavan-3-ols inhibit mammalian alpha-amylases but the published IC 50 and K i values vary up to a thousand times. We therefore tested the effects of 6 pure flavan-3-ols-abundant in green tea-on the activity of pure porcine pancreatic alpha-amylase (PPA) under steady-state kinetic conditions. We used both amylose and maltopentaose as substrates, along with spectrophotometry and chromatography as analytical tools, respectively. A Docking approach was also used to probe the interaction between PPA and each flavan-3-ol. The results showed that the 6 flavan-3-ols inhibit amylose hydrolysis with K i comprised between 7 and 34 μM, according to a mixed inhibition profile for gallocatechin gallate, and a competitive inhibition profile for the 5 other flavanols. Only the galloyl-containing flavan-3-ols inhibited the maltopentaose hydrolysis with a K i of about 30 μM according to a noncompetitive profile. We conclude that dietary flavan-3-ols could inhibit starch digestion nonnegligibly. The results of the docking trials were concordant with the kinetic data and have noticeably revealed that the cis-flavan-3-ols epigallocatechin gallate and epicatechin gallate bind similarly to PPA, involving π-stacking with Trp59.