中文摘要：

人血清白蛋白多种结合位点的存在使其成为许多药物可能的结合靶点.土贝母皂苷具有广泛的生理和药理活性,它与蛋白质相互作用机制的研究对于深入了解其药理药效具有重要的意义.采用荧光光谱法研究了土贝母皂苷II（TBMSⅡ）与人血清白蛋白（HSA）之间的相互作用,根据Stern-Volmer荧光淬灭方程计算得293,298,303,308 K时TBMSⅡ与HSA相互作用的结合常数分别为1.002×10^5,0.701×10^5,0.514×10^5,0.411×10^5 L·mol^-1.由实验计算出热力学参数焓变△H为-44.829 kJ·mol^-1,熵变△S为-57.497 J·mol^-1·K^-1,表明分子间的氢键及疏水作用是TBMSⅡ-HSA复合物的主要作用力,结合位点位于HSA的亚结构ⅡA,这与分子模拟方法的结果相一致.依据能量转移原理求得TBMSⅡ与HSA间的距离为4.95 nm;三维、同步荧光光谱及圆二色谱的结果表明TBMSⅡ的加入使HSA构象发生变化,α-螺旋结构有所下降.

英文摘要：

The presence of binding sites of human serum albumin makes it possible to combine many drugs target.The efficacy of tubeimosideII（TBMSII）,isolated from Bolbostemma paniculatum（Maxim）,binding to human serum albumin（HSA） is critical for pharmacokinetic behavior of TBMSII.The interactions between TBMSII and HSA under simulative physiological conditions were investigated by the methods of fluorescence spectroscopy.Fluorescence data revealed that the fluorescence quenching of HSA by TBMSII was the result of the formation of the TBMSⅡ-HSA complex.According to the modified Stern-Volmer equation,the binding constants（Ka） between TBMSⅡ and HSA at four different temperatures（293,298,303,308 K） were 1.002×10^5,0.701×10^5,0.514×10^5,0.411×10^5 Lomol-1 respectively.The thermodynamic parameters,enthalpy change（ΔH） and entropy change（ΔS） for the reaction were calculated to be -44.829 kJomol-1 and-57.497 Jomol-1oK-1 according to van＇t Hoff equation,indicating that the hydrogen bonds and hydrophobic interactions play a dominant role in the binding of TBMSII to HSA.Site marker competitive experiments indicated that the binding of TBMSⅡ to HSA primarily took place in sub-domain IIA,which was in good agreement with the results of molecular modeling study.The distance r between donor（HSA） and acceptor（TBMSII） was obtained to be 4.95 nm according to F rster＇s non-radioactive energy transfer theory.The conformational investigation showed that the presence of TBMSII decreased the α-helical content of HSA（from 22.7% to 19.58%） and induced the slight unfolding of the polypeptides of protein,which confirmed some micro-environmental and conformational changes of HSA molecules.