Abstract
Thermodynamic properties of lysozyme in binary solutions of water + dimethyl sulfoxide (DMSO) were studied paying attention to the intrinsic viscosity, the partial specific volume, the activation free energy for viscous flow, and the thermal denaturation of lysozyme. The thermostability and cooperativity of lysozyme for thermal denaturation was decreased and increased, respectively, with increasing the molar fraction of DMSO (x2). Lysozyme was stabilized (ΔΔG ＝－3 kJ mol －1) through the specific binding of DMSO at x2 ＝ 0.05. In the range of x2 ＝ 0.3 to 0.4, lysozyme was unfolded accompanied with increase in the intrinsic viscosity (Δ[η] ＝5.0 cm3 g －1), the partial specific volume (Δνo ＝ 0.023 cm3 g －1), and the activation free energy for viscous flow ((ΔΔμο*3＝1.4 ×103 kJ mol －1. It was considered that these changes were due to interfering water - lysozyme interaction through the strong water - DMSO interaction which was reflected in the maximum or minimum excess functions of the binary solution. The apparent partial specific volume of lysozyme was significantly dependent on the concentration of lysozyme and DMSO, indicating the preferential hydration or solvation to lysozyme. These results indicate that thermodynamic properties of protein in binary solutions together can sensitively reflect the conformational change of protein and the interaction with solvent.
https://ror.org/05kt9ap64 
