Abstract: The inhibitory effect of 1-deoxynojirimycin (DNJ) extracted from mulberry leaves on α-glycosidase was investigated by ultraviolet, fluorescence and circular dichroism (CD) spectroscopy. As a result, the half maximum inhibitory concentration (IC50) of DNJ α-glucosidase was 0.297 μg/mL. The type of inhibition was competitive. DNJ interacted with α-glucosidase through electrostatic attraction generating ground-state complexes and resulting in endogenous fluorescence quenching of α-glucosidase. The formation process of DNJ-α-glucosidase complexes was an entropy-driven endothermic reaction. The interaction was mainly driven by electrostatic attraction forces. At different temperatures (273, 298 and 310 K), fluorescence quenching constants (Ksv) were 1.48 × 104, 1.29 × 104, and 1.12 × 104 L/mol, respectively. DNJ resulted in a conformational change of α-glucosidase and rearrangement of the secondary structure inducing closing of the enzyme active pocket and consequently inhibiting substrate binding to the active center. These findings may explain the mechanism by which DNJ inhibited α-glucosidase activity and thus reduced blood glucose levels.

Key words: 1-deoxynojirimycin, α-glucosidase, hypoglycemic mechanism