In vitro inhibitory effects of Chinese bayberry (Myrica rubra Sieb. et Zucc.) leaves proanthocyanidins on pancreatic alpha-amylase and their interaction

Chinese bayberry leaves proanthocyanidins (BLPs) belongs to the prodelphinidin category with potent EGCG unit, whose inhibition effect on alpha-amylase and their interaction were investigated by in vitro digestion and enzyme kinetic analysis, multi fluorescence spectroscopies (fluorescence quenching, synchronous fluorescence, and three-dimensional fluorescence), circular dichroism spectra, Fourier transform infrared spectroscopy and in silico modelling. The results revealed that BLPs was a mixed inhibitor to alpha-amylase with the IC50 value of 3.075 +/- 0.073 mu g/mL. BLPs could lead to a static fluorescence quenching of alpha-amylase, mainly by means of interacting with amino acids (mainly Try and Tyr residues) in one site on alpha-amylase molecule under the action of hydrogen bonding and/or Van der Waals force. This interaction further induced the change of secondary conformational structure, functional group structure and hydrophobicity of alpha-amylase, thus resulting in lowering activity. Molecular docking simulated that this binding occurred in a cavity on the surface of the alpha-amylase molecule, and BLPs trimer showed a relatively high binding energy. The present study provided a new insight of BLPs as an alpha-amylase inhibitor, which could be considered in anti-diabetic therapy.