Shimizu Seishi, Matubayasi Nobuyuki
York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom.
Division of Chemical Engineering, Graduate School of Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan; Elements Strategy Initiative for Catalysts and Batteries, Kyoto University, Katsura, Kyoto 615-8520, Japan.
Biophys Chem. 2017 Dec;231:111-115. doi: 10.1016/j.bpc.2017.02.003. Epub 2017 Feb 27.
How osmolytes enhance the folding, binding, and self-assembly of biological macromolecules at a microscopic scale has long been a matter of debate. Ambiguities persist on the key interpretive concepts, such as the "effective membrane" (which marks the boundary of the volume from which osmolytes are excluded) and the "free energy of exclusion" of osmolytes from biomolecular surfaces. In this paper, we formulate these elusive concepts based upon chemical thermodynamics and rigorous statistical thermodynamics (the Kirkwood-Buff theory). Positioning of the membrane at the osmotic dividing surface is crucial in order not to affect the thermodynamics of solvation. The notion of the free energy (work) of excluding osmolytes is refined to the expansion work against the osmotic pressure, which indeed describes the change of solvation free energy at dilute osmolyte concentrations.
渗透压调节剂如何在微观尺度上增强生物大分子的折叠、结合和自组装，长期以来一直是一个有争议的问题。在关键的解释性概念上仍然存在模糊之处，例如“有效膜”（它标记了渗透压调节剂被排除在外的体积边界）和渗透压调节剂从生物分子表面的“排除自由能”。在本文中，我们基于化学热力学和严格的统计热力学（柯克伍德-布夫理论）来阐述这些难以捉摸的概念。将膜定位在渗透分界表面对于不影响溶剂化热力学至关重要。排除渗透压调节剂的自由能（功）的概念被细化为对抗渗透压的膨胀功，这确实描述了在稀渗透压调节剂浓度下溶剂化自由能的变化。
