Thermodynamic equations describing the volume behavior of protein-ligand mixtures in water were derived. In order to estimate the volume and binding parameters, the equations were combined with a Langmuir-type binding isotherm. Densities of aqueous solutions of mixtures of bovine serum albumin (BSA) and octanol (C8OH) were measured as a function of total BSA molality, mMT, at constant total C8OH molalities, mXT. The data were analyzed by the equations. The partial molar volumes at infinite dilution of BSA and C8OH, VMT,0 and VXT,0, respectively, were estimated. It was seen that VMT,0 decreases by the addition of C8OH to the solution and that VXT,0 decreases gradually with increasing mMT and approaches asymptotically to a certain value at high mMT. From the concentration dependence of VMT,0 and VXT,0, the values of the association constant K=392 kg mol-1, the maximum binding number bmax=1.9, and the volume change ΔV=-109 cm3 mol-1 were obtained for BSA-C8OH interaction in water. The negative value of ΔV indicates that the hydrophobic interaction reduces the protein volume and elevation of pressure promotes BSA-C8OH binding. These results is inconsistent with the pressure reversal of anesthesia.
All Science Journal Classification (ASJC) codes
- Surfaces and Interfaces
- Physical and Theoretical Chemistry
- Colloid and Surface Chemistry