Evaluation of the interactions between lipids and γ-globulin protein at the air-liquid interface

The interactions between lipids (cholesterol, distearoylphosphatidylcholine, distearoylphosphatidylethanolamine and sphingomyelin) and the gamma-globulin protein have been analyzed using the monolayer technique at the air-liquid interface. The analysis has been carried out using both state equations and an adequate thermodynamic formulation for the surface pressure (pi)-molecular area (a) isotherms. Different parameters as the virial coefficients, have been estimated. For the uncharged lipid monolayers, the interactions between the molecules are of an attractive nature, at medium and long distance, and of a steric repulsive nature at short distance. At low surface pressures the lipid molecules form small domains. The net force between gamma-Globulin molecules in the monolayers has been found to be attractive. Finally, it can be concluded that when the lipid monolayers are uncharged, there is practically no interaction between the protein and lipid molecules at the mentioned interface. (C) 1999 Elsevier Science B.V. All rights reserved.