| The major lipid components of myelin membrane, cerebroside, cholesterol, phospholipid and sulfatide have been studied by a number of physical techniques in single and multi-component systems.; The thermal and structural properties of anhydrous and hydrated natural cerebroside, sulfatide and synthetic C(,16)-cerebroside (NPGS) have been investigated by x-ray diffraction, differential scanning calorimetry and polarizing microscopy.; The hydrated synthetic C(,16)-cerebroside system has been shown to form a lamellar structure characterized by a highly ordered hydrocarbon chain packing arrangement. The crystal (--->) liquid crystal transition occurs at a high temperature (82(DEGREES)C) with an unusually high enthalpy change ((DELTA)H = 17.5 kcal/mole NPGS). The observed thermal and structural behavior, in addition to the known crystallographic structure of similar glycosphingolipid compounds, indicate that the stable hydrated crystal form E is stabilized by a lateral intermolecular hydrogen bonding network involving the sphingosine backbone, the galactosyl group and interbilayer water molecules.; An unusually stable "crystalline" phase of hydrated DPPC bilayers exhibiting increased hydrocarbon chain packing order and having a lower degree of hydration is also reported.; Calorimetric and structural data indicate miscibility of cerebroside and DPPC in the gel and liquid crystal states up to a ratio of NPGS:DPPC(, )(, )50 mole % cholesterol, binary mixtures of NPGS:cholesterol exhibit a low temperature ((TURN)50-60(DEGREES)C), low cooperativity crystal (--->) liquid transition, while the high temperature NPGS crystal (--->) NPGS liquid crystal transition is no longer present. In the liquid crystalline state cholesterol is miscible in melted NPGS bilayers up to a maximum solubility (TURN)50 mole %.; The maximum incorporation of cerebroside into DPPC:cholesterol (1:1, mole ratio) bilayers is (TURN)1:4.; The low miscibility of cerebroside in DPPC:cholesterol bilayers is attributed to the potential for intermolecular cerebroside-cerebroside association via the numerous hydrogen bond donor/acceptor groups of the galactosyl and sphingosine residues. |
