Myricetin inhibits the generation of superoxide anion by reduced form of xanthine oxidase

Myricetin, a plant-derived flavonol, was found to inhibit the formation of uric acid in a mixed-type manner with IC 50 value of (8.66   ±   0.03)   ×   10 −6   mol   L −1 and more potently inhibit the generation of superoxide anion (O 2 − ) catalysed by xanthine oxidase (XOD) with IC 50 value of (4.55   ±   0.02)   ×   10 −6   mol   L −1 . Inhibiting O 2 − generation by myricetin may be attributed to the reduced form of XOD with a substantially higher reduction potential for FADH /FADH 2 couple. Moreover, molecular docking verified that myricetin bound to the site around isoalloxazine ring in the flavin adenine dinucleotide (FAD) domain to block the diffusion of O 2 − out of the FAD site, resulting in the transfer of another electron from FADH 2 to O 2 − to form hydrogen peroxide. This study has provided new insight into the role of myricetin in inhibiting XOD catalysis, which may be beneficial to improve myricetin’s potential application in functional foods.