Partitioning of SDS in liposomes coated by the exopolymer excreted by Pseudoalteromonas antarctica NF3 as a measure of vesicle protection against this surfactant

Abstract

The capacity of glycoprotein (GP) excreted by Pseudoalteromonas antarctica NF3, to protect phosphatidylcholine (PC) liposomes against the action of the anionic surfactant sodium dodecyl sulfate (SDS) was studied in detail. To this end, changes in the surfactant partitioning between the lipid bilayer and the aqueous phase (partition coefficients, K) and in the effective surfactant to PC molar ratios (R e) were determined as a function of the amount of GP assembled with liposomes. The permeability of liposomes was determined by monitoring the changes in the fluorescence intensity of liposomes due to the release of the fluorescent dye 5(6)-carboxyfluorescein (CF) from the interior of vesicles to the bulk aqueous phase. Increasing GP amounts in the system resulted in the same interaction step as a rise in R e and a fall in the surfactant partitioning between the lipid bilayer and water. Hence, the higher the proportion of GP, the lower the surfactant ability to alter the permeability of liposomes and the lower its affinity with these bilayer structures. In addition, increasing GP proportions resulted in the same interaction step as a progressive increase of the free surfactant concentration (SW). The fact that the SW was always lower than the surfactant critical micelle concentration indicates that the interaction of SDS with coated liposomes was mainly ruled by the action of surfactant monomers in all cases.