SURFACE-PROPERTIES OF PROTEIN ALCOHOLIC SOLUTIONS .1. SURFACE-TENSION

The influence of ethanol on protein (e.g., bovine serum albumine (BSA)) adsorption from aqueous solutions has been investigated by surface tensiometry. The surface reaches a quasiequilibrium state resulting from the competitive adsorption of ethanol and BSA molecules. At less than 5%, v/v, ethanol content, kinetics of surface pressure increase results from the combination of two processes: a fast migration and adsorption that may be enhanced by a change in the state of BSA molecules in bulk solution (e.g., self-assembling), and a slow increase of surface pressure possibly caused by protein unfolding at the surface. These experiments made it possible to define a degree of BSA molecules unfolding. At 12%, v/v, ethanol content, the surface pressure kinetics display an overshoot effect. This effect results from the superposition of three processes: a very fast adsorption of BSA molecules, an irreversible desorption of some adsorbed BSA, and unfolding of the remaining BSA molecules. (C) 1994 Academic Press, Inc.