Interaction of urea and substituted ureas with polyglycine and certain proteins

Isopiestic equilibration measurements were made on ten protein-denaturant systems involving polyglycine, egg albumin, collagen, horse heart myoglobin, and the denaturants urea, 1,3-dimethylurea, 1,1-dimethylurea, and thiourea. The hydration of the proteins in the absence of denaturants is a function of the water activity and it is believed that this accounts, at least in part, for the varying hydration values found in the literature. The relative binding of water and denaturant to unfolded proteins was found to be a reversible process for which an equilibrium constant can be calculated. It was further found that in most cases the protein binds denaturant preferentially to water even in aqueous systems.