A.M. Butlerov Institute of Chemistry, Kazan Federal University, Kremlevskaya street, 18, Kazan 420008, Russia.
J Chem Phys. 2013 Aug 21;139(7):075102. doi: 10.1063/1.4818527.
The aim of this study is to simultaneously monitor the excess partial Gibbs energies, enthalpies, and entropies of water and white egg lysozyme and demonstrate how these quantities correlate with the coverage of the protein macromolecules by water molecules. Isothermal calorimetry and water sorption measurements were applied to characterize the hydration dependencies of the excess thermodynamic functions. The excess partial quantities are found to be sensitive to changes in the water and protein states. At the lowest water weight fractions (w1), changes in the excess functions are primarily attributable to the addition of water. The transition of lysozyme from a glassy (rigid) to a flexible (elastic) state is accompanied by significant changes in the excess partial quantities. When the charged groups on the protein are covered, this transition occurs at w1 = 0.05; when the coverage of both polar and weakly interacting surface elements is complete, the excess partial quantities become hydrated at w1 > 0.5. At the highest water content, water addition has no significant effect on the excess quantities. At w1 > 0.5, changes in the excess functions solely reflect changes in the state of the protein.
本研究旨在同时监测水和白卵溶菌酶的过剩偏摩尔 Gibbs 自由能、焓和熵，并展示这些量如何与水分子对蛋白质大分子的覆盖相关联。等温量热法和水吸附测量被应用于表征水合依赖性的过剩热力学函数。过剩的偏摩尔量对水和蛋白质状态的变化很敏感。在最低的水重量分数（w1）下，过剩函数的变化主要归因于水的加入。溶菌酶从玻璃态（刚性）到柔性（弹性）态的转变伴随着过剩偏摩尔量的显著变化。当蛋白质上的带电基团被覆盖时，这种转变发生在 w1 = 0.05 时；当极性和弱相互作用的表面元素的覆盖完全时，过剩偏摩尔量在 w1 > 0.5 时变得水合。在最高含水量时，水的加入对过剩量没有显著影响。在 w1 > 0.5 时，过剩函数的变化仅反映了蛋白质状态的变化。
