The adsorption of human plasma albumin and bovine pancreas ribonuclease at negatively charged polystyrene surfaces: I. Adsorption isotherms. Effects of charge, ionic strength, and temperature

Abstract

This paper describes the adsorption of human plasma albumin (HPA) and bovine pancreas ribonuclease (RNase) on polystyrene latices. The latices are homodisperse and emulsifier-free. Their surface charge is entirely due to sulfate groups. Important variables are the temperature, the pH, the KNO 3 concentration, and the surface charge on the latex. All isotherms reach well-defined plateaus, but otherwise HPA and RNase behave differently. HPA isotherms sometimes show steps or kinks, their initial slopes increase with temperature (except at low temperature at the isoelectric point), and the plateau values are more or less symmetrical with respect to the isoelectric point. RNase isotherms are of the “high affinity” type, with plateaus that are little sensitive to pH. Interpretation of the data points to an increase in entropy as one of the main driving forces of the process. The pronounced differences in adsorption behavior of HPA and RNase are attributed to the relatively easy adaptability of HPA molecules to changing conditions as compared with the relatively great conformational stability of RNase, so that adsorption reflects the structural coherence of the dissolved proteins.