Inhibition of α-glucosidase by vitamin D3 and the effect of vitamins B1 and B2

alpha-Glucosidase is a vital enzyme in carbohydrate metabolism. Over-expression of this enzyme is correlated with hyperglycemia. The inhibitory effect of vitamin D-3 on alpha-glucosidase as well as its mechanism of action was investigated in this work. The results showed that vitamin D-3 exhibited stronger inhibition on alpha-glucosidase than acarbose with the IC50 value of 1.28 x 10(-4) mol L-1, and the inhibition was a mixed-ype mechanism through a multiphase kinetic process. The inhibition constant was determined to be (5.66 +/- 0.03) x 10(-5) mol L-1. Vitamin D-3 interacted with alpha-glucosidase by hydrophobic interactions, and molecular docking further verified that the inhibitor inserted into the active site pocket of alpha-glucosidase and interacted with the amino residues, which induced the rearrangement and conformational changes of alpha-glucosidase, and might move to cover the active pocket, hindering the binding of the substrate leading to the inhibition of the enzyme activity. Moreover, it was found that vitamin D-3 combined with vitamin B-1 or vitamin B-2 exhibited significant synergistic effects on inhibition of alpha-glucosidase. This study has provided new insights into the role of vitamin D-3 in inhibiting alpha-glucosidase catalysis and offered useful information on the dietary recommendation of vitamin D-3 for the treatment of type 2 diabetes.