Abstract
In the concentration range of 10 −5 to 10 −1 M Ca 2+ modulates the thermotropic properties of several neutral and anionic glycosphingolipids (galactosylceramide, asialo-G M1, sulfatide, G M1, G D1a, G T1b) and of their mixtures with dipalmitoylphosphatidylcholine. The transition temperature of gangliosides is not appreciably changed while the transition enthalpy increases by 20% in the presence of Ca 2+. The more marked effect of Ca 2+ is on the thermotropic behavior of systems containing sulfatide. Increasing concentrations of Ca 2+ between 10 −5 and 10 −3 M (up to a molar ratio of Ca 2+/sulfatide 1:2) induce a progressive increase of both the transition temperature and enthalpy. Further increases up to 10 −1 M Ca 2+ induce a new phase transition at a lower temperature. No evidence is found for induction of phase separation of pure glycosphingolipid-Ca 2+ domains in mixtures of any of the glycosphingolipids with dipalmitoylphosphatidylcholine. The modification of the phase behavior of anionic glycosphingolipids by Ca 2+ does not involve detectable variations of the intermolecular packing but is accompanied by marked modifications of the dipolar properties of the polar head group region.
Published Version
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