Protection of liposomes against triton X-100 by means of the new exopolymer excreted by Pseudoalteromonas antarctica NF3

The capacity of the glycoprotein (GP) excreted by Pseudoalteromonas antarctica NF3, to protect phosphatidylcholine (PC) liposomes against the action of Triton X-100 (TX-100) was studied in detail. Increasing GP amounts in the system led to a progressive adsorption of this compound on the surface of liposomes in equilibrium with the free GP in the aqueous phase. This fact resulted for the same interaction step in an increase in the effective surfactant to PC molar ratios (Re) and in a fall in the surfactant partitioning between lipid bilayer and the aqueous phase (partition coefficients K). Thus, the higher the proportion of GP in the system the lower the surfactant ability to saturate and solubilize PC liposomes and the lower its affinity with these bilayer structures. In addition, increasing GP proportions resulted in a progressive increase of the free surfactant concentration (SW) needed to saturate or solubilize liposomes. The fact that SW at sublytic and lytic level was lower and similar (slightly higher) than the surfactant critical micelle concentration indicates that the interaction at these two levels was mainly ruled by the action of surfactant monomers and by the formation of complex mixed micelles surfactant/PC/GP.