Mechanism of binding interactions between young apple polyphenols and porcine pancreatic α-amylase.

The binding interactions between young apple polyphenols and porcine pancreatic α-amylase were investigated through isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC) and molecular docking. The results obtained were compared with those obtained through inhibition kinetics and fluorescence quenching. It was found that binding of tannic acid, chlorogenic acid, caffeic acid and epicatechin with α-amylase is an exothermal process, with the binding constants in the order of tannic acid > chlorogenic acid > caffeic acid > epicatechin. This is consistent with the orders of reciprocal of competitive inhibition constant and fluorescence quenching constant. The binding energy obtained through molecular docking showed the same order, except for epicatechin. These results are consistent with the inhibition of α-amylase being caused by the binding of the polyphenols with the enzyme. In addition, from the fluorescence quenching and DSC data, total polyphenols, tannic acid, chlorogenic acid and caffeic acid were found to partially unfold the enzyme structure.