The Calculation of Partial Specific Volumes of Proteins in 6 M Guanidine Hydrochloride

This chapter presents a method to calculate the apparent partial specific volumes of proteins in 6M Guanidine Hydrochloride (GuHCl), which greatly reduces the uncertainties inherent in the previously used procedures. The only information required is the amino acid composition of the protein. The buoyancy of a sedimenting protein may be affected by GuHCl denaturation. It has been found that the major change in the buoyancy is due to the interactions of the denatured protein with solvent components and that the change in volume of protein upon denaturation in 6 M GuHCl is generally small, its effect on the partial specific volume of the protein being negligible. The chapter also presents the calculation for α-chymotrypsin to illustrate that the amino acid composition of the protein is expressed as residues per 10⁵ grams of protein. For the glycoproteins, additional GuHCl binding to the protein is calculated by assuming that each residue of carbohydrate binds one molecule of GuHCl. In the case of coenzyme A transferase, the total carbohydrate contents are only about 1.6% by weight. Therefore, the final results are essentially identical whether or not the corrections for additional GuHCl binding to carbohydrates are made.