INFLUENCE OF THE CHOLESTEROL ON DOMAIN FORMATION IN THREE-PHASE LIPOSOME SYSTEM

Krunoslav Mirosavljević and Vesna Nöthig-Laslo

Ruđer Bošković Institute, Croatia

In order to investigate the possibility of domains formation in lipid membranes due to the presence of cholesterol, multilamellar liposomes composed of egg-phosphatidylcholine and dicetylphosphate with various amounts of cholesterol were prepared. Liposomes were spin-labelled with stearic acids containing the nitroxide group bound at various carbon atoms along the fatty acid chain. From the parameters of the Electron Spin Resonance (ESR) spectra of nitroxides[1] (line width, hyperfine splitting constant) order parameter for the phospholipids chains was determined and was compared for liposomes with different amounts of cholesterol (0, 8, 15, 29, 38 and 45 mol %). Penetration of water into hydrophobic interior of the lipid membranes[2], [3] with different amounts of cholesterol was measured by pulsed ESR technique ESEEM (Electron Spin Echo Envelope Modulation). Those measurements gave information about hydrophobic barrier in the liposomes. The presented results indicate formation of domains in the multilamellar liposomes as a function of cholesterol. [1] D. Marsh, Electron Spin Resonance (from Membrane Spectroscopy), Springer-Verlag, Berlin Heidelberg, 1981, pages 51-142. [2] V. Nöthig-Laslo, P. Cevc, D. Arčon, M. Šentjurc, Origin of Life and Evolution of the Biosphere. 34 (2004) 237-242. [3] V. Nöthig-Laslo, P. Cevc, D. Arčon, M. Šentjurc, Applied Magnetic Resonance. 27 (2004) 303-309.

Email: laslo@irb.hr

Address: Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia