Abstract
Thermal unfolding of ribonuclease A (RNase), lysozyme, and α-chymotripsinogen A was analyzed in various aqueous solutions. The equilibrium between [unfolding]/[folding] ratio was correlated well to the water activity (aw) of the solution, which was described well by the modified Wyman-Tanford equation. This shows the important role of aw in protein stability. From this analysis, the change in hydration number (Δi) upon protein unfolding was obtained. Thus obtained Δi was much smaller than that based on the change in the accessible surface area in protein unfolding. By the integration of the reciprocal Wyman-Tanford plot, the free energy difference (ΔΔG) for protein stability in a solution and in pure water was calculated. TheΔΔG showed linear relationships with the concentration of solute, in most cases. This provides a theoretical basis for the empirical linear extrapolation model (LEM).
