Tang Jianghong, Wang Weiping, Luan Feng, Chen Xingguo
Department of Chemistry, Lanzhou University, Lanzhou 730000, PR China.
Int J Biol Macromol. 2005 Oct 30;37(1-2):85-91. doi: 10.1016/j.ijbiomac.2005.08.010. Epub 2005 Oct 10.
5,7,4'-trihydroxy-6,3',5'-trimethoxyflavone is one of the bioactive components isolated from Artemisia plants possessing antitumor therapeutic activities. In this paper, its binding properties and binding sites located on human serum albumin (HSA) have been studied using UV absorption spectroscopy, fluorescence spectroscopy and Fourier transform infrared (FT-IR) spectra. The results of fluorescence titration revealed that 5,7,4'-trihydroxy-6,3',5'-trimethoxyflavone could strongly quench the intrinsic fluorescence of HSA by static quenching and there was only one class of binding sites on HSA for this drug. The binding constants at four different temperatures (289, 298, 310, and 318 K) were 1.93, 1.56, 1.22, and 0.93x10(5) L mol-1, respectively. The FT-IR spectra evidence showed that the protein secondary structure changed with reduction of alpha-helices about 27.6% at the drug to protein molar ratio of 3. The thermodynamic functions standard enthalpy change (DeltaH0) and standard entropy change (DeltaS0) for the reaction were calculated to be -18.70 kJ mol-1 and 36.62 J mol-1 K-1 according to the van't Hoff equation. These results and the molecular modeling study suggested that hydrophobic interaction was the predominant intermolecular force stabilizing the complex, and 5,7,4'-trihydroxy-6,3',5'-trimethoxyflavone could bind to the site I of HSA (the Warfarin Binding site).
5,7,4'-三羟基-6,3',5'-三甲氧基黄酮是从具有抗肿瘤治疗活性的蒿属植物中分离出的生物活性成分之一。本文利用紫外吸收光谱、荧光光谱和傅里叶变换红外光谱（FT-IR）研究了其与人血清白蛋白（HSA）的结合特性及结合位点。荧光滴定结果表明，5,7,4'-三羟基-6,3',5'-三甲氧基黄酮可通过静态猝灭强烈猝灭HSA的内在荧光，且该药物在HSA上只有一类结合位点。四个不同温度（289、298、310和318 K）下的结合常数分别为1.93、1.56、1.22和0.93×10⁵ L·mol⁻¹。FT-IR光谱证据表明，在药物与蛋白质摩尔比为3时，蛋白质二级结构发生变化，α-螺旋减少约27.6%。根据范特霍夫方程，该反应的热力学函数标准焓变（ΔH⁰）和标准熵变（ΔS⁰）经计算分别为-18.70 kJ·mol⁻¹和36.62 J·mol⁻¹·K⁻¹。这些结果和分子模拟研究表明，疏水相互作用是稳定复合物的主要分子间作用力，且5,7,4'-三羟基-6,3',5'-三甲氧基黄酮可与HSA的位点I（华法林结合位点）结合。
