New insights into the interactions between dark blue pigment from Vaccinium bracteatum Thunb leaves and digestive enzymes

Abstract

The dark blue pigment from Vaccinium bracteatum Thunb. leaves (VBTL) is a healthy ingredient for controlling postprandial blood glucose during the stage of dietary carbohydrate digestion. Our previous study has proved that the dark blue pigment has an inhibition effect on pancreatic α-amylase. However, the influence on other digestive enzymes (α-glucosidases, trypsin, and α-chymotrypsin) is still unclear. Therefore, this research evaluated the impact of this dark blue pigment on the three digestive enzymes during in-vitro digestion. The effects of dark blue pigment on the activities and conformations of the α-glucosidase, trypsin, and α-chymotrypsin were confirmed by multi-spectroscopic techniques and molecular docking. The results showed that this pigment possessed a higher inhibition ability on the α-glucosidase. The complexes of three enzymes and the pigment all resulted in the changes in fluorescence quenching and secondary structures of these complexes. However, the interactions between two proteolytic enzymes and pigment slightly impacted their activities. Additionally, molecular docking suggested that the complex between α-glucosidase and pigment formed hydrogen bonds and hydrophobic interactions in the substrate-binding pocket. These findings provide creative insight into the VBTL dark blue pigment controlling postprandial hyperglycemia without side effects on the proteolytic enzymes.