ABSTRACT
The effect of added ethanol and (NH(4))(2)SO(4) on the flux decline index (FDI) of bovine serum albumin (BSA) and a fatty acid-poor derivative (BSA/FAP) was examined. Ternary phase diagrams of the two protein species indicated that the concentration polarization (CP) layer on the surface of a nonadsorbing 10 000 MWCO regenerated cellulose membrane had principally a packed bed structure up to 33 wt % ethanol and 21 wt % (NH(4))(2)SO(4). Intrinsic viscosity and turbidity analysis were conducted to determine the degree of intra- and interprotein interactions within this packed bed morphology. With BSA/FAP, the effects of these two interactions tended to counterbalance each other, so the FDI of this protein was not strongly influenced by solute addition. In contrast, the adsorption of fatty acids to BSA caused the protein to expand, producing a less rigid CP layer with a higher FDI. However, the addition of ethanol led to protein compression, reducing this effect. The presence of fatty acids also produced a more associated BSA in salt solution, which increased flux resistance. The results obtained for both proteins indicate that an FDI minimum is observed when a noninteraction hard sphere structure is present in the CP layer.
Subject(s)
Serum Albumin, Bovine/chemistry , Ultrafiltration/methods , Adsorption , Animals , Cattle , Ethanol/chemistry , Fatty Acids/chemistry , Membranes, Artificial , Nephelometry and Turbidimetry , Solubility , Solutions , Surface Properties , Viscosity , Water/chemistryABSTRACT
Ternary phase diagrams (TPDs) for aqueous bovine serum albumin (BSA) solutions containing ethanol or (NH4)2SO4 were determined for temperatures ranging from 20 to 70 degrees C. At 20 degrees C, ethanol destabilized BSA, resulting in gel formation at moderate solute concentrations. In contrast, (NH4)2SO4 concentrations above 20 wt % precipitated BSA from solution. Raising the temperature led to gel formation at increasingly lower BSA and solute concentrations. The removal of adsorbed fatty acids from BSA had little effect on the ethanol TPDs but reduced protein solubility in (NH4)2SO4. Moreover, the salt TPDs of fatty-acid-poor BSA were similar to those previously observed with S-ovalbumin.
