de Lauzon S, Rajkowski K M, Cittanova N
Département de Biochimie, Faculté de Médecine, Paris, France.
J Steroid Biochem Mol Biol. 1994 Feb;48(2-3):225-33. doi: 10.1016/0960-0760(94)90149-x.
Quantitative understanding of steroid hormone transport and receptor-mediated action requires knowledge of the bonding forces involved in each steroid-protein complex and the effects of a biological environment on these forces. An approach to these problems using dilute solutions of water-miscible organic solvents, with a range of polarity, dielectric and hydrogen bonding properties, was tested on an estradiol-antiestradiol antibody binding system on the basis that comparing the effects of the solvents would both permit the importance of hydrophobic and hydrogen bonding to be differentiated and give information on the effects of the environment on the reaction. The results were compared with thermodynamic measurements. All the solvents reduced the Gibbs free energy of binding as a function of their concentration in the medium. The decreases were virtually a monotonic function of their dielectric constant, indicating reduced hydrogen bonding. Analysis of the decreases in terms of the solvents' hydrogen bonding and polarity properties supported this. Thermodynamic measurement showed the binding reaction was enthalpy-driven with, overall, a slightly unfavorable entropy contribution. This again showed the hydrophobic effect was not the main bonding force. The most deleterious solvent, iso-propanol, not only decreased the enthalpic contribution to binding but rendered the entropic contribution more favorable. This approach still does not allow the relative importance of hydrogen bonding and van der Waals contacts in the actual binding to be differentiated but it does give indications on how a biological environment may affect a steroid-protein binding reaction in vivo.
对类固醇激素转运和受体介导作用的定量理解需要了解每个类固醇 - 蛋白质复合物中涉及的结合力以及生物环境对这些力的影响。基于比较溶剂的影响既能区分疏水作用和氢键作用的重要性，又能提供有关环境对反应影响的信息，一种使用具有不同极性、介电常数和氢键性质的与水混溶的有机溶剂稀溶液来解决这些问题的方法，在雌二醇 - 抗雌二醇抗体结合系统上进行了测试。将结果与热力学测量结果进行了比较。所有溶剂都降低了结合的吉布斯自由能，其降低程度是介质中溶剂浓度的函数。降低程度实际上是其介电常数的单调函数，表明氢键作用减弱。根据溶剂的氢键性质和极性对降低程度进行分析支持了这一点。热力学测量表明结合反应是由焓驱动的，总体上熵的贡献略有不利。这再次表明疏水作用不是主要的结合力。最具破坏性的溶剂异丙醇不仅降低了对结合的焓贡献，还使熵贡献变得更有利。这种方法仍然无法区分氢键作用和范德华接触在实际结合中的相对重要性，但它确实给出了有关生物环境可能如何影响体内类固醇 - 蛋白质结合反应的线索。
