Biology Reference
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However, lateral diffusion in the l o state is almost as great as in the liquid crystalline state.
Since acyl chains are extended by cholesterol, membrane domains that are rich in cholesterol
tend to be thicker than regions that are devoid of the sterol. Since lipid rafts are highly
enriched in cholesterol, they are thicker than the surrounding non-raft membrane.
A DSC Study
In Figure 9.24 it was shown that cholesterol slightly lowers the T m , substantially broadens
the main transition, and diminishes the
H of DPPC in lipid bilayers. More than a decade
before the advent of lipid rafts, van Dijck et al. [7] and Demel et al. [8] realized they could
use the obliteration of T m s to monitor relative affinities of cholesterol for various phospho-
lipids. van Dijck's 1976 experiment, outlined in Figure 10.3 , compared PC to PE. The exper-
iments were based on having two phospholipids with T m s sufficiently far apart that their
D
16:0,16:0 PC
18:1,18:1 PC
(a)
²H
- CHOL
+ CHOL
T o C
18:1,18:1 PC
14:0,14:0 PE
(b)
²H
- CHOL
+ CHOL
T o C
16:0,16:0 PC
18:1,18:1 PE
(c)
²H
- CHOL
+ CHOL
T o C
FIGURE 10.3 Relative affinity of cholesterol for PC and PE as detected by DSC. In Panel (a) cholesterol is shown
to preferentially obliterate the lower melting transition (18:1,18:1 PC
16:0,16:0 PC) when both transitions are for
the same phospholipid type (PC in this example). In Panel (b) cholesterol is shown to preferentially obliterate the
lower melting 18:1,18:1 PC over the higher melting 14:0,14:0 PE. In Panel (c), where the T m s of PC and PE are
reversed, cholesterol preferentially obliterates 16:0,16:0 PC even though its T m is higher than that of 18:1,18:1 PE.
This experiment was interpreted as evidence that cholesterol associates more strongly with PCs than with PEs.
(Experiment is redrawn from [7] ).
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