Interaction mechanism between α-glucosidase and A-type trimer procyanidin revealed by integrated spectroscopic analysis techniques

alpha-Glucosidase is an important enzyme in human intestine, and inhibition of its activity can lower blood sugar levels to effectively prevent hyperglycaemia induced tissue damage. Here, we investigated the inhibitory activities of procyanidins with different structures on alpha-glucosidase and the underlying mechanism. The results showed that the IC50 of catechin and compounds 2-7 on alpha-glucosidase was lower than that of acarbose. A-type procyanidins might have better inhibitory activity than B-type procyanidins. In addition, there was no positive correlation between the polymerization degree of A-type procyanidin oligomer and its inhibitory effect on alpha-glucosidase. Compound 7 (A-type trimer) with the best inhibitory effect reversibly inhibited the activity of alpha-glucosidase in a mixed-type manner. Fluorescence data confirmed that the intrinsic fluorescence of alpha-glucosidase was quenched by compound 7 through static-dynamic quenching. The calculated thermodynamic parameters indicated that their binding was spontaneous and driven by hydrophobic interaction, which was also confirmed by the UV spectrum experiment. Besides, circular dichroism analysis displayed that their binding resulted in conformational changes of alpha-glucosidase characterized by a decrease in alpha-helix and an increase in beta-sheet. The results demonstrate the ability of procyanidins to intervene in the progression of type 2 diabetes by inhibiting alpha-glucosidase. (C) 2019 Elsevier B.V. All rights reserved.