Partial Specific Volumes and Interactions with Solvent Components of Proteins in Guanidine Hydrochloride

The partial specific volumes of twelve proteins were determined by density measurements. For these proteins in their native state, the determined values of partial specific volumes are generally in good agreement with the accepted literature values except in the case of bovine α-lactalbumin. The determined value of 0.704 is similar to that found for lysozyme. Preferential interaction parameters of 6 m guanidine hydrochloride with these proteins were also measured. For the twelve proteins studied, the preferential interaction with solvent components varies between 0 and 0.17 g of guanidine hydrochloride per g of protein. In no case is interaction preferential with water. The total binding of denaturant to protein is calculated and the correlation between the observed and expected number of denaturant molecules bound is found to be good, if peptide bonds and aromatic side chains are taken as the binding sites. The changes in volume upon transfer from dilute salt to 6 m guanidine hydrochloride of the proteins studied are calculated and compared with theoretical values reported in the literature.