Turnbull W Bruce, Daranas Antonio H
Astbury Centre for Structural Molecular Biology, School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK.
J Am Chem Soc. 2003 Dec 3;125(48):14859-66. doi: 10.1021/ja036166s.
Isothermal titration calorimetry (ITC) allows the determination of DeltaG degrees, DeltaH degrees, and DeltaS degrees from a single experiment and is thus widely used for studying binding thermodynamics in both biological and synthetic supramolecular systems. However, it is widely believed that it is not possible to derive accurate thermodynamic information from ITC experiments in which the Wiseman "c" parameter (which is the product of the receptor concentration and the binding constant, K(a)) is less than ca. 10, constraining its use to high affinity systems. Herein, experimental titrations and simulated data are used to demonstrate that this dogma is false, especially for low affinity systems, assuming that (1) a sufficient portion of the binding isotherm is used for analysis, (2) the binding stoichiometry is known, (3) the concentrations of both ligand and receptor are known with accuracy, and (4) there is an adequate level of signal-to-noise in the data. This study supports the validity of ITC for determining the value of K(a) and, hence, DeltaG degrees from experiments conducted under low c conditions but advocates greater caution in the interpretation of values for DeltaH degrees. Therefore, isothermal titration calorimetry is a valid and useful technique for studying biologically and synthetically important low affinity systems.
等温滴定量热法（ITC）能够通过单次实验测定ΔG°、ΔH°和ΔS°，因此被广泛应用于研究生物和合成超分子体系中的结合热力学。然而，人们普遍认为，在Wiseman“c”参数（即受体浓度与结合常数K(a)的乘积）小于约10的ITC实验中，无法获得准确的热力学信息，这限制了其在高亲和力体系中的应用。在此，通过实验滴定和模拟数据表明这一教条是错误的，特别是对于低亲和力体系，前提是：（1）结合等温线的足够部分用于分析；（2）结合化学计量已知；（3）配体和受体的浓度准确已知；（4）数据中有足够的信噪比。本研究支持ITC在低c条件下进行的实验中确定K(a)值以及由此确定ΔG°的有效性，但主张在解释ΔH°值时要更加谨慎。因此，等温滴定量热法是研究具有生物学和合成重要性的低亲和力体系的一种有效且有用的技术。
