Galactocerebroside-phospholipid interactions in bilayer membranes.
Differential scanning calorimetry (DSC) and x-ray diffraction have been used to study the interaction of hydrated N-palmitoylgalactosylsphingosine (NPGS) and dipalmitoylphosphatidylcholine (DPPC). For mixtures containing less than 23 mol% NPGS, complete miscibility of NPGS into hydrated DPPC bilayers is observed in both the bilayer gel and liquid-crystal phases. X-ray diffraction data demonstrate insignificant differences in the DPPC-bilayer gel-phase parameters on incorporation of up to 23 mol% NPGS. At greater than 23 mol% NPGS, additional high-temperature transitions occur, indicating phase separation of cerebroside. For these cerebroside concentrations, at 20 degrees C, x-ray diffraction shows two lamellar phases, hydrated DPPC-NPGS gel bilayers (d = 64 A) containing 23 mol% NPGS, and NPGS "crystal" bilayers (d = 55 A). On heating to temperatures greater than 45 degrees C, the mixed DPPC-NPGS bilayer phase undergoes chain melting, and on further increasing the temperature progressively more NPGS is incorporated into the liquid-crystal DPPC-NPGS bilayer phase. At temperatures greater than 82 degrees C (the transition temperature of hydrated NPGS), complete lipid miscibility is observed at all DPPC/NPGS molar ratios.
D002151:Calorimetry; D002554:Cerebrosides / Q000502:physiology*; D005699:Galactosylceramides / Q000502:physiology*; D008051:Lipid Bilayers; D008560:Membrane Fluidity; D008563:Membrane Lipids / Q000502:physiology*; D010743:Phospholipids / Q000502:physiology*; D011663:Pulmonary Surfactants; D014961:X-Ray Diffraction
D002554:Cerebrosides; D005699:Galactosylceramides; D008051:Lipid Bilayers; D008563:Membrane Lipids; D010743:Phospholipids; D011663:Pulmonary Surfactants