Open AccessThe interaction of phosphatidylcholine bilayers with Triton X‐100
Author(s) -
GOÑI Félix M.,
URBANEJA MariaAngeles,
ARRONDO José Luis R.,
ALONSO Alicia,
DURRANI Aziz A.,
CHAPMAN Dennis
Publication year - 1986
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1986.tb10088.x
Subject(s) - phospholipid , chemistry , phosphatidylcholine , pulmonary surfactant , lipid bilayer , triton x 100 , differential scanning calorimetry , popc , vesicle , analytical chemistry (journal) , bilayer , chromatography , fourier transform infrared spectroscopy , crystallography , membrane , thermodynamics , chemical engineering , biochemistry , physics , engineering
The interaction of multilamellar phosphatidylcholine vesicles with the non‐ionic detergent Triton X‐100 has been studied under equilibrium conditions, specially in the sub‐lytic range of surfactant concentrations. Equilibrium was achieved in less than 24 h. Estimations of detergent binding to bilayers, using [ 3 H]Triton X‐100, indicate that the amphiphile is incorporated even at very low concentrations (below its critical micellar concentration); a dramatic increase in the amount of bound Triton X‐100 occurs at detergent concentrations just below those producing membrane solubilization. Solubilization occurs at phospholipid/detergent molar ratios near 0.65 irrespective of lipid concentration. The perturbation produced by the surfactant in the phospholipid bilayer has been studied by differential scanning calorimetry, NMR and Fourier‐transform infrared spectroscopy. At low detergent concentration (lipid/detergent molar ratios above 3), a reduction in 2 H‐NMR quadrupolar splitting occurs, suggesting a decrease in the static order of the acyl chains; the same effect is detected by Fourier‐transform infrared spectroscopy in the form of blue shifts of the methylene stretching vibration bands. Simultaneously, the enthalpy variation of the main phospholipid phase transition is decreased by about a third with respect to its value in the pure lipid/water system. For phospholipid/detergent molar ratios between 3 and 1, the decrease in lipid static order does not proceed any further; rather an increase in fluidity is observed, characterized by a marked decrease in the midpoint transition temperature of the gel‐to‐fluid phospholipid transition. At the same time an isotropic component is apparent in both 31 P‐NMR and 2 H‐NMR spectra, and a new low‐temperature endotherm is detected in differential scanning calorimetric traces. When phospholipid and Triton X‐100 are present at equimolar ratios some bilayer structure persists, as judged from calorimetric observations, but NMR reveals only one‐component isotropic signals. At lipid/detergent molar ratios below unity, the NMR lines become narrower, the main (lamellar) calorimetric endotherm tends to vanish and solubilization occurs.