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Electrostatic effects in lysine and polylysine adsorption at lipid membrane surface were studied. Electrokinetic measurements demonstrated that lysine induces similar dose dependent changes of zeta potential in suspensions of liposomes made from cardiolipin (CL) and phosphatidylserine (PS). These changes correlate well with numerical description of diffuse part of electric double layer by Gouy-Chap man-Stern model in assumption that both potassium cation and lysine molecules determine the ionic strength of the media. Good agreement with the electrokinetic data was found with the isotherm constructed for lysine distribution between bilayer and water with low constant (K d = 1.2 × 10 -3 M -1 ) independently of potassium adsorption (K = 1 M -1 ) on lipid molecules or for their competitive adsorption with the same con stants. Lysine adsorption induces total boundary potential changes of planar bilayer lipid membranes (BLM) from the same lipids registered by the method of intramembranous field compensation. In contrast to surface potential of liposomes in electrokinetic experiments the total boundary potential of BLM remains unchanged up to concentration of lysine that is about 1.5 orders of magnitude higher. This fact corresponds to changes in opposite directions of surface and dipole components of boundary potential. They compensate each other to some extent when lysine adsorbs at the surface. This explanation was supported by molecular dynamic sim ulation of bilayers from DOPS in the presence of lysine. According to the MD simulations, the compensation effect can be attributed to lysine effect on hydrogen bonds of water molecules with phosphate groups of lipids but not with carboxylic groups. A similar "compensation effect" was expected and observed with membranes from CL and PS. The amplitude of dipole effect was about 40 mV due to the lysine-lipid interactions and corresponded well to the amplitude of the slow phase in the boundary potential changes induced by polylysine adsorption on planar BLM. This phase can be attributed to polypeptide conformational changes and/or lipid bilayer restructuring phenomena.

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