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Abstract
Lactosylceramide (LacCer) is a pivotal intermediate in the metabolism of higher gangliosides,
localizes to sphingolipid-sterol "rafts," and has been implicated in cellular signaling.
To provide a fundamental characterization of LacCer phase behavior and intermolecular
packing, LacCer containing different saturated (16:0, 18:0, 24:0) or monounsaturated
(18:1(Delta9), 24:1(Delta15)) acyl chains were synthesized and studied by differential
scanning calorimetry and Langmuir film balance approaches. Compared to related sphingoid-
and glycerol-based lipids, LacCers containing saturated acyl chains display relatively
high thermotropic and pressure-induced transitions. LacCer monolayer films are less
elastic in an in-plane sense than sphingomyelin films, but are somewhat more elastic
than galactosylceramide films. Together, these findings indicate that the disaccharide
headgroup only marginally disrupts gel phase packing and orients more perpendicular
than parallel to the interface. This contrasts the reported behavior of digalactosyldiglycerides
with saturated acyl chains. Introducing single cis double bonds into the LacCer acyl
chains dramatically lowers the high thermotropic and pressure-induced transitions.
Greater reductions occur when cis double bonds are located near the middle of the
acyl chains. The results are discussed in terms of how an extended disaccharide headgroup
can enhance interactions among naturally abundant LacCers with saturated acyl chains.