Comparative evaluation of tannic acid inhibiting α-glucosidase and trypsin

In this work, the inhibitory effects of tannic acid on the α-glucosidase and trypsin were systematically evaluated by comparing with the clinical diabetes healer acarbose and the soybean-derived trypsin inhibitor using fluorescence spectroscopy and enzymatic kinetics methods. We showed that the anti-α-glucosidase activity of tannic acid (IC 50   =   0.44   μg/mL) was higher than that of acarbose (IC 50   >   0.60   μg/mL), while its anti-trypsin activity (IC 50   =   0.79   mg/mL) was significantly lower than that of the trypsin inhibitor from soybean (IC 50   <   0.20   mg/mL). Enzymatic kinetics measurements confirmed that the inhibitory pattern of tannic acid toward two tested enzymes was a mixed competitive and noncompetitive inhibition. Tannic acid could bind the enzymes to form new complexes, presenting a strong static fluorescence quenching. The presence of tannic acid led to the hypsochromic shift of the maximum fluorescence in trypsin, but not in α-glucosidase. The thermodynamic parameters indicated that the main driving force between tannic acid and both the enzymes was the hydrophobic interaction followed by the electrostatic interaction. Our work suggests that tannic acid is a strong anti-α-glucosidase natural inhibitor with a low inhibitory activity for trypsin, thus its roles in functional food and medicinal plants should be re-recognized.