Osmotic Pressure of Bovine Serum Albumin in the Presence of Sodium-based Salts at Moderate Ionic Strength
Authors:Larry Chang, Danielle Ornelas, Noriko Ozaki-Felt
Mentor:Victor G.J Rodgers, Department Chair of Bioengineering and Professor of Bioengineering, UC Riverside
Previously, our lab developed a free-solvent model that predicted the non-linear protein osmotic pressure for concentrated bovine serum albumin (BSA) in 0.15 M NaCl at pH 7.4 that was consistent with experimental data (1). In this study, we investigate how anions affect the osmotic pressure of BSA in the presence of 0.15 M monovalent sodium salt solutions at pH 7.4. In particular, this work focuses on NaF and NaI. Reboiras et al. (1986) utilized an empirical model to examine the binding of potassium salts to BSA at high protein concentrations using data from an EMF apparatus (2). Their work predicted that the salt ion binding values for F- and I- are 3 mol NaF/mol BSA and 11 mol NaI/mol BSA , respectively, for 0.1 M salt solutions at pH 7. In our work, osmotic pressure data of BSA in 0.15 M NaF and NaI at pH 7.4 were obtained up to saturation. Using non-linear least squares regression on the osmotic pressure data, the predicted model parameters were determined to be 7.5 0.58 mol NaF/mol BSA and 1.2 1.06 mol NaI/mol BSA for ion binding and 0.97 ± 0.035 g H2O/g BSA and 0.68 ± 0.052 g H20/g BSA, for NaF and NaI solution hydration, respectively. The ion binding values were significantly different than those previously determine by using an EMF method (2). Interestingly, the model-regressed hydration values for NaI implied an increase saturation limit for the protein in solution which was observed and is consistent with the literature (1). Our current results also show that the monotonic consistency between osmotic pressure and salt ion position in the Hofmeister series was not observed. This is primarily because the solution anions alter the protein-hydration, protein-ion binding as well as salt water interactions, all which dictate the resulting osmotic pressure.