Effect of polysaccharides on the inhibition and binding ability of hesperetin-copper(II) complex on α-glucosidase

The study aimed to investigate the inhibitory effect of hesperetin-copper (II) [Hsp-Cu(II)] on α-glucosidase in the presence of polysaccharides (xylan, β-glucan, low-, medium- and high-viscosity chitosan). The results showed that all the polysaccharides significantly reduced the inhibitory activity of α-glucosidase by Hsp-Cu(II), and the reduction effect of high-viscosity chitosan was the most significant. The polysaccharides significantly decreased the binding constant of Hsp-Cu(II)α-glucosidase, changed the binding sites of Hsp-Cu(II) to α-glucosidase and reduced the hydrogen bonds of Hsp-Cu(II) bound with α-glucosidase. Circular dichroism showed that the reduction of α-helix content in α-glucosidase caused by Hsp-Cu(II) was raised from 27.2 % to 29.5 %, 31.3 % and 32.7 % in the presence of xylan, β-glucan and high-viscosity chitosan, respectively, suggesting that the polysaccharides could restore the secondary structure of α-glucosidase. Fourier transforms infrared spectra showed that xylan and β-glucan formed hydrogen bonds with Hsp-Cu(II). The mechanism of the decreasing effect might be that the polysaccharides with the low viscosity compete with α-glucosidase to bind Hsp-Cu(II) through hydrogen bonds, restoring the catalytic center and active amino acid residues of Hsp-Cu(II) bound with α-glucosidase and the adsorption of high-viscosity chitosan decreases the binding affinity of Hsp-Cu(II) on α-glucosidase. The study may offer a reference for the development of Hsp-Cu(II)-based nutritional and healthy food for patients with hyperglycemia.