Thermal unfolding of ribonucrease A (RNase) in osmolyte (betaine, sarcosine, trehalose) solutions could be described well by the van't Hoff equation. All the osmolytes used stabilized RNase. Effect of osmolyte concentration on unfolding ratio of RNase at a constant temperature was described well by the reciprocal Wyman-Tanford plot based on water activity. Effect of cosolute on thermal stability of protein could be explained by the balance between the stabilization effect by hydration and the destabilization effect of cosolute binding to protein. By the integration of the reciprocal Wyman-Tanford equation, the stabilization free energy of protein in a solution as compared with that in pure water,Δ Δ G, could be obtained theoretically.
