Inhibition Effect and Molecular Mechanism of Hypericin on Xanthine Oxidase

Dietary flavonoid has been reported to possess a high potential for inhibition xanthine oxidase (XOD). Herein, hypericin was investigated for its inhibition effect and interaction mechanism on XOD by enzyme inhibition kinetics, multi-spectroscopy and molecular docking. Enzyme kinetics analysis indicated that hypericin reversibly inhibited XOD in a mix-competitive manner with IC₅₀ value of (162.059±2.291) μmol/L and inhibition constant (Ki) value of (18.079±0.154) μmol/L. Multi-spectroscopy displayed that hypericin bound to XOD with high affinity, and the interaction was predominately driven by hydrogen bond and van der Waals forces. Circular dichroism (CD) demonstrated that hypericin induced the conformational change of XOD with increased α-helix and Random coil while reduced β-sheet and β-turn. Molecular docking suggested that hypericin interacted with residues located within the active pocket of XOD (e.g. GLN767, GLY797 and PHE798). These results would provide experimental and theoretical basis for hypericin in development of functional food or drug.