Biology Reference
In-Depth Information
FIGURE 13.11
Fatty acid profile of liver phospholipids determined by GC on a Carbowax stationary phase
column (Alltech)
[34]
. The mobile gas phase was helium and the temperature profile was 100
C for 2 min, 195
C for
33 min and 220
C up to the end. Temperature ramp was 40
C/min. Each fatty acid is identified by three numbers;
number of carbons, number of double bonds, and the series (omega-family). Elution time is on the abscissa and the
detector intensity on the ordinate. The area under each curve represents the relative amount of each fatty acid.
D. MODEL LIPID BILAYER MEMBRANES
LIPOSOMES
e
In previous sections of this chapter the importance of detergents in membrane studies was
discussed and how membrane integral proteins and polar lipids (including phospholipids,
gangliosides, and cholesterol) can be isolated. The next step involves reconstituting a func-
tional membrane using detergents, polar lipids, and integral proteins. But first, model,
protein-free, stable lipid bilayer vesicles, commonly known as liposomes, will be described.
Model Membranes
Biological membranes are so complex that they often defy comprehensive analysis. For
this reason a variety of relatively simple model membrane systems have been developed.
The simplest model consists of membrane lipids dissolved in organic solution. Obviously
this model is extremely limited as it has no three dimensional structure that in any way
resembles a membrane. Its primary application is in following very short distance molecular
interactions, mainly lipid
lipid associations. The oldest model membrane is the lipid mono-
layer, discussed in Chapter 2. Lipid monolayers have their origins in a very distant, murky
past. Although monolayers are only one half of a bilayer, they formed the foundation for
modern membrane biophysical studies. The first stable lipid bilayer was reported by Mueller
et al. in 1962
[36]
. This model membrane, introduced in Chapter 9, was made by spreading an
organic solution of membrane polar lipids across a small (~1mm) hole in a teflon partition
separating two aqueous chambers (
Figure 13.12
)
[37]
. Initially a thick glob of lipid in organic
e
