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 antarct ica NF3, to protect phosphatidylcholine (PC) liposomes against the action o f 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 r esulted for the same interaction step in an increase in the effective surfa ctant to PC molar ratios (Re) and in a fall in the surfactant partitioning between lipid bilayer and the aqueous phase (partition coefficients K). Thu s, the higher the proportion of GP in the system the lower the surfactant a bility to saturate and solubilize PC liposomes and the lower its affinity w ith these bilayer structures. In addition, increasing GP proportions result ed in a progressive increase of the free surfactant concentration (S-W) nee ded to saturate or solubilize liposomes. The fact that S-W at sublytic and lytic level was lower and similar (slightly higher) than the surfactant cri tical micelle concentration indicates that the interaction at these two lev els was mainly ruled by the action of surfactant monomers and by the format ion of complex mixed micelles surfactant/PC/GP. (C) 2000 Elsevier Science B .V. All rights reserved.