PROTEIN ADSORPTION AND PROTEIN-LIPID INTERACTIONS AT THE AIR-AQUEOUS SOLUTION INTERFACE

In this work we studied BSA (bovine serum albumin) adsorption and BSA- monostearin interactions at the air-aqueous solution interface. Both t he surface tension-time dependence and equilibrium surface tension wer e determined using the Wilhelmy plate method. Temperature, protein con centration in the aqueous phase, the concentration of the lipid spread on the interface and the aqueous phase composition (ethanol and sucro se) were the variables studied. The following conclusions were drawn. (a) The rate of BSA adsorption at the interface increases with both BS A concentration in the aqueous phase and temperature. (b) With ethanol in the subphase the existence of an induction period is observed, whi ch could reflect the existence of BSA-solute interactions in the aqueo us phase and at the interface. (c) The rate of BSA adsorption increase s when sucrose is present in the bulk phase. (d) The spreading of mono stearin at the interface on a protein him causes a rapid reduction in surface tension which can be associated with a displacement of protein by the lipid. After the initial period, surface tension increases wit h time until the equilibrium surface tension - similar to that of the lipid - is reached, indicating that protein is displaced by monosteari n at the interface. (e) When the amount of monostearin spread on the i nterface is increased, BSA-monostearin interactions both at the interf ace and in the aqueous bulk phase increase as well. (f) Protein-lipid interactions depend on both protein concentration and aqueous phase co mposition.