ION-EXCHANGE OF PROTEINS - A MICROCALORIMETRIC STUDY OF THE ADSORPTION OF BOVINE SERUM-ALBUMIN ON ANION-EXCHANGE MATERIALS

The adsorption of bovine serum albumin (BSA) at two anion-exchange materials has been studied using a high-sensitivity titration calorimeter. This technique can uniquely provide thermodynamic information for such processes. Isotherm data have also been collected, the adsorption being a reversible process. Even though the adsorption data could be correlated reasonably well using an isotherm with a single equilibrium constant, the experimental enthalpies of adsorption showed systematic variations as the amount of protein adsorbed increased. This is direct evidence of variation in the nature of binding as the ion-exchange materials became loaded with protein. The two ion-exchangers showed very different behavior. For Whatman QA52 (a cellulosic, quaternary amine-bearing, strong anion-exchanger) the adsorption process was endothermic, except for the first part of the adsorption process at low ionic strength. As the adsorption was spontaneous under all conditions studied, this indicates that the adsorption process was entropy driven, except for the first part at low ionic strength. For Polymer Laboratories PL-SAX 1000 (a strong-union fully quaternized polyethyleneimine structure coupled to a synthetic polymer matrix) the adsorption process was exothermic, except for the first part of the adsorption at low ionic strength. This indicates that enthalpy played a significant part in driving the process, except for the first part at low ionic strength. Possible reasons for these differences are discussed. © 1993 Academic Press, Inc.