Rapid screening and identification of α-glucosidase inhibitors from mulberry leaves using enzyme-immobilized magnetic beads coupled with HPLC/MS and NMR

alpha-Glucosidase plays important roles in the digestion and absorption of carbohydrates in the small intestine. The inhibition of alpha-glucosidase is regarded as a potential way to treat diabetes. We established an approach to screening alpha-glucosidase inhibitors from medicinal plants using enzyme-coated magnetic bead. Using 1-(3-dimethyl-aminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide as reaction reagents, alpha-glucosidase was immobilized on the magnetic beads by covalent linkage. The conjugation of alpha-glucosidase to the magnetic beads was characterized using scanning electron microscope and X-ray diffractometer. The proposed approach was applied in fishing potential alpha-glucosidase inhibitors from extract of Morus alba, a Chinese medicinal plant. The structures of potential active compounds were identified via liquid chromatographymass spectrometry and nuclear magnetic resonance. The results demonstrated that two flavonoids (isoquercitrin and astragalin) could bind to alpha-glucosidase, which was confirmed via conventional alpha-glucosidase inhibitory assay. Our findings suggested that enzyme-coated magnetic beads may be suitable for discovering active compounds from medicinal plants. Copyright (c) 2012 John Wiley & Sons, Ltd.