Kinetic analysis of inhibition of α-glucosidase by leaf powder from and its component iminosugars.

Unlabelled: Mulberry leaves contain iminosugars, such as 1-deoxynojirimycin (1-DNJ), fagomine, and 2--α-D-galactopyranosyl deoxynojirimycin (GAL-DNJ) that inhibit α-glucosidase. In this study, we quantified iminosugars in leaves and made the kinetic analysis in the hydrolysis of maltose by α-glucosidase. By LC-MS/MS, the concentrations of 1-DNJ, fagomine, and GAL-DNJ in the powdered leaves were 4.0, 0.46, and 2.5 mg/g, respectively, and those in the roasted ones were 1.0, 0.24, and 0.73 mg/g, respectively, suggesting that the roasting process degraded iminosugars. Steady-state kinetic analysis revealed that the powdered and roasted leaves exhibited competitive inhibition. At pH 6.0 at 37ºC, the IC values of the extracts from the boiled powdered or roasted leaves were 0.36 and 1.1 mg/mL, respectively. At the same condition, the IC values of 1-DNJ, fagomine, and GAL-DNJ were 0.70 μg/mL, 0.18 mg/mL, and 2.9 mg/mL, respectively. These results suggested that in , 1-DNJ is a major inhibitor of α-glucosidase.

Abbreviations: 1-DNJ: 1-deoxynojirimycin; GAL-DNJ: 2-O-α-D-galactopyranosyl-DNJ.