Abstract:

The inhibition mechanism of morin on xanthine oxidase (XO) in phosphate buffer (pH 7.5) was investigated by
UV-vis absorption, fluorescence and circular dichroism spectroscopy combined with molecular simulation technique. The
results showed that morin could be a good reversible XO inhibitor in a mixed-type manner with an inhibitory concentration
leading to a 50% loss in the activity (IC50) and an inhibition constant (Ki) of 1.35 × 10–5 mol/L and 1.21 × 10–5 mol/L,
respectively. Strong fluorescence quenching and secondary structure changes of XO were observed due to the formation of
a complex with morin. The results from molecular simulation have further confirmed that morin was mainly bound to the
active site of XO where it interacted with some primary amino acid residues such as Phe914, Phe649, Phe1009, Leu648,
Leu1014, Leu873, etc. by hydrophobic force. It could be concluded that morin inhibited XO catalytic activity by entering
into XO’s hydrophobic cavity, blocking the insertion of substrate xanthine and influencing the formation of active center.

Key words: morin, xanthine oxidase, inhibition kinetics, binding characteristics, spectroscopic techniques, molecular simulation