title: The effect of sterols on structures formed in the gel/subgel phase state of dipalmitoylphosphatidylcholine bilayers.
abstract: The effect of cholesterol and lanosterol on the formation of structures in the gel/subgel phase of 1,2-dipalmitoylphosphatidylcholine was investigated using freeze-fracture electron microscopy and X-ray diffraction. Mixtures with up to 25 mol% sterol were analysed after annealing for between several days and some months at 4 degrees C. Bilayers of DPPC with 5 or 10 mol% sterol showed a domain structure in the gel state. There are rounded or lens-like and often inclined plates within less smooth either plane or striped bilayer areas. The stripes are formed by parallel lines separated by a distance of 30-60 nm. Parallel lines can be induced also in the less smooth but plane areas by warming up to 25 degrees C. X-ray diffraction showed two lamellar repeat spacings at 6.45 and 8.3 nm in both 5 and 10 mol% samples. The plates are interpreted as domains of (nearly) pure DPPC within the sterol containing bilayer. Stripes are present if the concentration of cholesterol is below a critical value (approx. 15 mol%). With time of incubation at 4 degrees C curved deformations appear in parts of the bilayers. Two main types are formed. The small type has a repeat distance of about 100 nm and the large type of about 400 nm. The curved deformations were progressively flattened by warming up to 25-32 degrees C with an accompanying reappearance of stripes but no plates. After prolonged annealing at 4 degrees C there is also the formation of regular ripples. It is concluded that in presence of 5 and 10 mol% sterol in bilayers of 1,2-dipalmitoy-phosphatidylcholine the immiscibility of gel phase and subgel phase changes during prolonged annealing at 4 degrees C. We assume a rearrangement of the molecules into a homogeneous phase state with liquid-ordered properties.
authors.affiliation: Institute of Ultrastructure Research, Friedrich-Schiller-University Jena, Germany.
authors.forename: H W
authors.initials: HW
authors.lastname: Meyer
authors.forename: K
authors.initials: K
authors.lastname: Semmler
authors.forename: P J
authors.initials: PJ
authors.lastname: Quinn
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002784:Cholesterol / Q000737:chemistry*; D005614:Freeze Fracturing; D007810:Lanosterol / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008854:Microscopy, Electron; D019906:Nuclear Magnetic Resonance, Biomolecular; D012542:Scattering, Radiation; D014965:X-Rays
chemical_list: D008051:Lipid Bilayers; D007810:Lanosterol; D015060:1,2-Dipalmitoylphosphatidylcholine; D002784:Cholesterol