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

The capacity of glycoprotein (GP) excreted by Pseudoalteromonas antarctica NF3, to protect phosphatidylcholine (PC) liposomes against the action of th e 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 sur factant to PC molar ratios (R-e,) were determined as a function of the amou nt of GP assembled with liposomes. The permeability of liposomes was determ ined by monitoring the changes in the fluorescence intensity of liposomes d ue to the release of the fluorescent dye 5(6)-carboxyfluorescein (CF) from the interior of vesicles to the bulk aqueous phase. Increasing GP amounts i n the system resulted in the same interaction step as a rise in R-e and a f all in the surfactant partitioning between the lipid bilayer and water. Hen ce, the higher the proportion of GP. the lower the surfactant ability to al ter the permeability of liposomes and the lower its affinity with these bil ayer structures. In addition, increasing GP proportions resulted in the sam e interaction step as a progressive increase of the free surfactant concent ration (S-w). The fact that the Sw was always lower than the surfactant cri tical micelle concentration indicates that the interaction of SDS with coat ed liposomes was mainly ruled by the action of surfactant monomers in all c ases.