PARTITIONING AND LOCALIZATION OF SPIN-LABELED AMANTADINE IN LIPID BILAYERS - AN EPR STUDY

EPR was used to study the distribution of the spin-labeled amantadine (AA-SL) between the bulk hydrophobic-hydrocarbon solvent, light paraff in oil, and water and between hydrophobic-hydrocarbon chain region of lipid membranes and water. The AA-SL molecules were soluble in both hy drophobic and polar regions of investigated systems. It was shown that the partition coefficient of AA-SL between the hydrocarbon region of the L-alpha-dimyristoylphosphatidylcholine fluid-phase membrane and wa ter is much higher than between bulk hydrocarbon solvent and water. Fu rthermore, the partitioning of AA-SL into membranes of multilamellar l iposomes made of L-alpha-dimyristoylphosphatidylcholine, L-alpha-dipal mitoylphosphatidylcholine, and L-alpha-distearoylphosphatidylcholine w as studied as a function of temperature, indicating no abrupt change a t the main phase transition of these membranes. It is also clear from our data that AA-SL can penetrate into the gel-phase membrane practica lly with the same partitioning as into the fluid-phase membrane. Furth ermore, it was shown that at least part of the AA-SL molecule is deepl y buried in the hydrocarbon chain region of the membrane.