Analyzing the Effects of Protecting Osmolytes on Solute–water Interactions by Solvatochromic Comparison Method: II. Globular Proteins

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Partitioning of 11 globular proteins was examined in aqueous dextran–PEG–sodium/potassium phosphate buffer (0.01 M K/NaPB, pH 7.4) two-phase systems (ATPSs) containing 0.5 M sorbitol. The data obtained were analyzed together with those reported previously for the same proteins in osmolyte-free ATPS and ATPS containing 0.5 M sucrose, TMAO, or trehalose. It was found that all the partition coefficients for proteins determined in the presence of 0.5 M of different osmolytes and in the absence of osmolytes may be described in terms of the differences between solvent properties of the coexisting phases. Solute-specific coefficients characterizing different types of solute–solvent interactions were calculated for each protein. These solute-specific coefficients are linearly interrelated implying cooperativity of different types of protein–water interactions. The data obtained indicate the lack of any association of the aforementioned osmolytes at concentration of 0.5 M with proteins. Computational analysis of one of the solute-specific coefficient Ss-values characterizing dipole–dipole protein–water interactions shows that it is determined by the peculiarities of protein surface.

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RSC Advances, v. 5, issue 73, p. 59780-59791