Interactions of proteins with solvent components in 8 m urea

The interaction between proteins and urea was investigated by determining the apparent partial specific volumes of nine proteins in the molecular weight range 9000 to 41,000 in 8 m urea solution and comparison with values reported in the literature for various denaturants showed good agreement.

Abstract

The interaction between proteins and urea was investigated by determining the apparent partial specific volumes of nine proteins in the molecular weight range 9000 to 41,000 in 8 m urea solution. The apparent partial specific volumes were determined under both isomolal and isopotential conditions. The preferential interaction with solvent components, calculated from the obtained values, varied between zero and 0.14 g of urea per gram of protein. In none of the cases was the interaction preferential with water. The total binding of denaturant to each protein was calculated and the correlation between the total number of residues and the number of moles of urea bound per mole of protein was obtained. Several models were tested for the observed and expected number of denaturant molecules bound to the protein. A good correlation was obtained for the model in which one urea molecule was bound to each pair of peptide units and one to each aromatic side chain. There was no correlation whatever with protein hydrophobicity. The changes in volume upon transferring the proteins from dilute salt solution to 8 m urea were calculated; comparison with values reported in the literature for various denaturants showed good agreement.