桑色素对黄嘌呤氧化酶活性的抑制作用

在磷酸盐缓冲体系（pH 7.5）中，利用紫外光谱法、荧光光谱法和圆二色谱法，结合分子模拟技术研究了桑色素对黄嘌呤氧化酶（xanthine oxidase，XO）活性的抑制机理。结果表明：桑色素是一种有效的可逆性混合型抑制剂，其半数抑制浓度（IC50）和抑制常数（Ki）分别为1.35×10–5 mol/L和1.21×10–5 mol/L；桑色素通过疏水作用力与XO形成基态复合物导致XO内源荧光的猝灭，并诱导XO的二级结构发生改变；分子模拟结果进一步证实桑色素主要通过疏水作用力结合到XO的活性中心，与Phe914、Phe649、Phe1009、Leu648、Leu1014和Leu873等主要氨基酸发生作用。推测桑色素进入XO的疏水腔，阻碍了底物黄嘌呤进入XO活性中心并影响了XO活性中心的形成，从而抑制了XO对黄嘌呤的催化活性。

Inhibition Effect of Morin on Xanthine Oxidase Activity

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.