Pethica Brian A
Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA.
Anal Biochem. 2015 Mar 1;472:21-9. doi: 10.1016/j.ab.2014.11.010. Epub 2014 Dec 4.
Isothermal titration calorimetry (ITC) has given a mass of data on the binding of small molecules to proteins and other biopolymers, with particular interest in drug binding to proteins chosen as therapeutic indicators. Interpretation of the enthalpy data usually follows an unsound protocol that uses thermodynamic relations in circumstances where they do not apply. Errors of interpretation include incomplete definitions of ligand binding and equilibrium constants and neglect of the non-ideality of the solutions under study, leading to unreliable estimates of standard free energies and entropies of binding. The mass of reported thermodynamic functions for ligand binding to proteins estimated from ITC enthalpies alone is consequently of uncertain thermodynamic significance and utility. ITC and related experiments to test the protocol assumptions are indicated. A thermodynamic procedure avoiding equilibrium constants or other reaction models and not requiring protein activities is given. The discussion draws attention to the fundamental but neglected relation between the thermodynamic activity and bioactivity of drugs and to the generally unknown thermodynamic status of ligand solutions, which for drugs relates directly to effective therapeutic dosimetry.
等温滴定量热法（ITC）已提供了大量关于小分子与蛋白质及其他生物聚合物结合的数据，尤其关注作为治疗指标的药物与蛋白质的结合。焓数据的解释通常遵循一种不合理的方案，即在不适用的情况下使用热力学关系。解释错误包括配体结合和平衡常数的定义不完整，以及忽视所研究溶液的非理想性，从而导致对标准自由能和结合熵的估计不可靠。因此，仅根据ITC焓估计的配体与蛋白质结合的大量报道的热力学函数具有不确定的热力学意义和实用性。文中指出了ITC及相关实验以检验方案假设。给出了一种避免平衡常数或其他反应模型且不需要蛋白质活度的热力学方法。讨论提请注意药物的热力学活性与生物活性之间基本但被忽视的关系，以及配体溶液普遍未知的热力学状态，而对于药物来说，这直接关系到有效的治疗剂量测定。
