Number of galloyl moiety and intramolecular bonds in galloyl-based polyphenols affect their interaction with alpha-glucosidase

The inhibition of alpha-glucosidase by nine galloyl-based polyphenols with free and unfree galloyl moieties (GMs) was studied. The results show that the inhibitory activity increased with the free GM number increasing. For the compounds with unfree GMs, ellagic acid and hexahydroxydiphenoyl group contributed to the enzyme inhibition. Free GMs could bind not only with the active site of alpha-glucosidase (competitive inhibition character), but also with the non-active sites (uncompetitive one); however, the former binding interaction was stronger than the latter one. All polyphenols that had inhibitory effects quenched alpha-glucosidase fluorescence in a static mode through forming a polyphenol-enzyme complex. The number of amino acid residues involved in polyphenolenzyme binding interactions (hydrogen bonding and pi-conjugations) increased with the inhibitory activity increasing. Additionally, two polyphenols with 5 free GMs showing certain hypoglycemic effects in maltose-loading test suggests that GM may be an advisable functional factor for alleviation of type II diabetes symptoms.

Automated summary

The study found that the inhibitory activity of alpha-glucosidase increased with the number of free galloyl moieties, while unfree galloyl moieties mainly contributed to inhibition through ellagic acid and hexahydroxydiphenoyl group. The polyphenols could form a static complex with the enzyme through binding interactions, and the number of amino acid residues involved in these interactions was positively correlated with inhibitory activity.