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Molecular distribution and charge of polylysine layers at the surface of lipid membranes and mica


Electrophoretic mobility of cardiolipin liposomes was measured in the presence of polylysines of different molecular weight at various concentrations of the background electrolyte (KCl). The electrophoretic mobility in a liposome suspension changes its sign and reaches a plateau at high polylysine content. The surface charge in the plateau region was determined according to the Gouy-Chapman model of the electrical double layer. The average charge density was found to equal 0.005 and 0.016 Coulomb/m2 for the polymer length of 5 and 12 units (bases), respectively, and 0.032 Coulomb/m2 for polylysines with the length of 130 and 1435 units. The molecular distribution of these polylysines was studied at the mica surface using atomic force microscopy in the 10-mM KCl solution. It was shown that pentalysine molecules covered uniformly about 90% of the surface with the layer thickness of about 0.8 nm. The high-molecular polylysines cover about 60% of the surface with the layer thickness of more than 1.5 nm. The data suggest that the polymer forms a compact layer on the membrane surface; the charge density at the outer surface is determined both by the polymer properties and by the total amount of anionic lipids, irrespective of their ionization state.

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Correspondence to Yu. A. Ermakov.

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Original Russian Text © O.A. Finogenova, O.V. Batischev, A.V. Indenbom, V.I. Zolotarevsky, Yu.A. Ermakov, 2009, published in Biologicheskie Membrany, 2009, Vol. 26, No. 5, pp. 429–436.

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Finogenova, O.A., Batischev, O.V., Indenbom, A.V. et al. Molecular distribution and charge of polylysine layers at the surface of lipid membranes and mica. Biochem. Moscow Suppl. Ser. A 3, 496 (2009).

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Key words

  • polylysines
  • pentalysine
  • lipid membranes
  • cardiolipin
  • liposomes
  • electrophoretic mobility
  • surface charge
  • mica surface