Comparison of Inhibitory Activities and Mechanisms of Five Mulberry Plant Bioactive Components against α-Glucosidase

The a-glucosidase inhibitory effects of five bioactive components, namely I-deoxynojirimycin, cyanidin-3-glucoside, cyanidin-3-rutinoside, resveratrol and oxyresveratrol contained in mulberry (Morus, Moraceae) plants have been compared. Spectroscopy methods were employed to compare their alpha-glucosidase inhibitory mechanisms. The results revealed that 1-deoxynojirimycin (competitive), resveratrol and oxyresveratrol (noncompetitive) were stronger inhibitors than acarbose, while cyanidin-3-glucoside and cyanidin-3-rutinoside (mix competitive and noncompetitive) showed modest activities. IDeoxynojirimycin, resveratrol and oxyresveratrol could quench the fluorescence spectra statically by forming stable complexes, while the quenching of cyanidin-3-rutinoside and cyanidin-3-glucoside belonged to dynamic quenching by the collision of molecules. The interactions between ligands and alpha-glucosidase were mainly driven by hydrophobic force, or hydrogen bonding consequently induced conformational changes and reduced surface hydrophobicity. Docking results suggested that they could bind to alpha-glucosidase at different sites. This work provides useful information for the understanding of the ligands a-glucosidase interactions and identifies oxyresveratrol as a potent alpha-glucosidase inhibitor.