On the Interaction of Triton X-100 with Multilamellar Phosphaticylcholine Liposomes

Abstract

The interaction of the non-ionic detergent Triton X-100 with multilamellar phosphatidylcholine liposomes has been studied under sub-lytic and lytic conditions by a variety of chemical and physical methods. Solubilization was tested by turbidimetric, centrifugation and filtration techniques; in all cases 50% solubilization was observed at lipid: surfactant molar ratios (R) near 0.5. ³¹ P-NMR and ² H-NMR spectroscopy reveal the coexistence of bilayer and micellar phases in slow interchange for R > 1 and a sigle isotropic phase at R < 1. Differential scanning calorimetry of DPPC/Triton X-100 mixtures also reveals a thermotropic transition that could be ascribed to free lipid-surfactant mixed micelles at R < 1. No increase in bilayer permeability to 6-carboxyfluorescein was observed at sub-lytic surfactant concentrations. ³¹ P-NMR fails to reveal any changes in phospholipid headgroup conformation or mobility except those directly related to phase changes, but Fourier-transform infrared spectroscopy does indicate significant changes in the phosphate vibrational transitions upon solubilization. H-NMR, calorimetric and IR spectroscopic observations confirm that the presence of surfactant monomers in the bilayer reduces the static order of the phospholipid hydrocarbon chains, decreases the gel-to-liquid crystalline transition temperature of the lipid, and facilitates the anti-gauche rotations in the lipid matrix.