Influence of Ionic Strength on Adsorption of Polypeptides on Lipid Membranes: Theoretical Analysis

Theoretical analysis of the effect of the ionic strength of a solution on the surface (zeta) potential of liposomes formed by an anionic phospholipid (cardiolipin) with adsorbed polycations has been carried out. The experimental data were previously measured by the electrokinetic method in the presence of polylysine molecules of different molecular weights and a supporting electrolyte, KCl, at concentrations of 10, 40, and 100 mM. To approximate the experimental dependences of the potential on the amount of polylysine in the suspension, we used a theoretical model with parameters, among which the most physically significant are the thickness of the polymer layer, the adsorption constant, and the fraction of the surface of lipid membranes occupied by the polypeptide at the saturation. The found values of the model parameters demonstrate the effect of the length of the polypeptide molecules on the structure of the polymer layer varying from homogeneous to clustered distribution over the surface. A noticeable decrease in the efficiency of adsorption with an increase in the ionic strength of the solution is explained by the conformational rearrangements of the macromolecules on the surface and a decrease in the area of the surface available for their adsorption upon the saturation.