title: Complex phase mixing of phosphatidylcholine and phosphatidylserine in multilamellar membrane vesicles.
abstract: The phase mixing in dipalmitoyl phosphatidylcholine and bovine brain phosphatidylserine mixtures suspended in aqueous salt solutions was studied by differential scanning calorimetry, freeze-fracture electron microscopy and X-ray and electron diffraction. The pure dipalmitoyl phosphatidylcholine has two well-defined solidus phases P beta' and L beta' and a liquidus phase L alpha while the pure phosphatidylserine has a broad transition from L beta to L alpha. The mixture exhibits some dipalmitoyl phosphatidylcholine characteristics up to 30% phosphatidylserine when pure P beta' phase no longer exists. Phase mixing is observed at all compositions. An addition of 3% phosphatidylserine is found to be sufficient to destroy the sharp L beta'--P beta' transition observed in pure dipalmitoyl phosphatidylcholine. The transition between L beta' and P beta' in these mixtures is displaced to lower temperatures and becomes gradual as depicted by all three techniques, but freeze-fracture gives more definite information of the continuous transition. The most striking observation on the morphology of the mixed membranes (3--30% phosphatidylserine in dipalmitoyl phosphatidylcholine) is the presence of banded patterns (P beta') at temperatures well below the main transition peak as detected by differential scanning calorimetry.
mesh_terms: D002152:Calorimetry, Differential Scanning; D005614:Freeze Fracturing; D008567:Membranes, Artificial; D008854:Microscopy, Electron; D008968:Molecular Conformation; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D014961:X-Ray Diffraction
chemical_list: D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D010718:Phosphatidylserines