Interactions of Spread Lecithin Monolayers with Bovine Serum Albumin in Aqueous Solution

The dynamics of surface pressure (Π) and of surface concentration (Γ) of 14C radiolabeled bovine serum albumin (BSA) adsorbed onto spread lecithin monolayers at the air−water interface were measured. The adsorption of BSA onto spread lecithin monolayers of 107 and 64 Å2/molecule was enhanced at short times (within a few seconds), indicating synergism due to possible dissolution of BSA molecules into loosely or moderately packed lecithin layers. The surface concentration of BSA increased to 2−2.5 mg/m2 from about 1 mg/m2 and the surface pressure to 20−35 mN/m from about 10 mN/m in the presence of spread lecithin monolayer. At long times, monolayer composition was found, however, to be dominated by lecithin. BSA was expelled from the interface by close-packed lecithin monolayers, possibly because of the surface pressure and steric exclusion effects.