A. Saez-cirion et al., Sphingolipids (galactosylceramide and sulfatide) in lamellar-hexagonal phospholipid please transitions and in membrane fusion, LANGMUIR, 16(23), 2000, pp. 8958-8963
The effects of galactosylceramide (cerebroside) and sulfogalactosylceramide
(sulfatide) from bovine brain on the lamellar-to-inverted hexagonal phase
transition of dielaidoylphosphatidylethanolamine are examined using differe
ntial scanning calorimetry. When mixed with dielaidoylphosphatidylethanolam
ine, cerebroside increases the transition temperature (ca. 0.2 degreesC/mol
% added cerebroside) and increases the transition DeltaH. Sulfatide increa
ses the transition temperature by ca. 0.4 degreesC/mol. % added sulfatide a
nd decreases DeltaH. Both lipids are seen to hinder the formation of the no
nlamellar phase, although sulfatide is more effective in this respect. When
incorporated into vesicles formed by phosphatidylcholine/phosphatidylethan
olamine/ cholesterol (2:1:1 mole ratio), which are a good substrate for pho
spholipase C and undergo fusion as a consequence of the enzyme activity (Ni
eva et al. Biochemistry 1989, 28, 7364), cerebroside at all concentrations
and sulfatide at > 5 mol % inhibit enzyme activity and vesicle fusion. Cere
broside inhibition of fusion is due not only to a reduced enzyme activity b
ut also to the impaired formation of nonlamellar phases. Sulfatide at low c
oncentrations (e.g., 1 mol %) enhances phospholipase C activity and vesicle
fusion, probably because its net negative charge causes hyperpolarization
of the interface, which is known to activate phospholipase C. Under these c
onditions, its enzyme-activating effect predominates over its bilayer-stabi
lizing properties. Thus, sulfatide at low concentrations is an exception to
the rule that amphiphiles hindering the lamellar-hexagonal transition inhi
bit both phospholipase C activity and membrane fusion.