Polypeptides on the Surface of Lipid Membranes. Theoretical Analysis of Electrokinetic Data

Abstract

A theoretical model describing experimental data on the electrophoretic mobility of liposomes, which are formed from mixtures of charged (cardiolipin) and neutral (phosphatidylcholine) lipids and contain polylysine molecules adsorbed on them, is considered. The experimental data show that the ζ potential of the liposomes depends on the concentration of the adsorbed polylysine. The proposed model is used to determine the physically measured characteristics describing the system: the thickness of the adsorbed polymer layer, the surface area fraction occupied by the polymer at saturation, and the polymer–liposome surface binding constant. The performed calculations show that the reversibility of the adsorption dramatically decreases with an increase in the sizes of adsorbed polymer molecules. In addition, the presented model explains the behavior of the point of zero charge upon variations in the system parameters. The considered model is not confined to a specific type of polymers and phospholipids and may be used to study the adsorption of other biologically significant synthetic polycations and polypeptides.