Biology Reference
In-Depth Information
a BLM is well suited for trans-membrane electrical measurements, it is very prone to vibra-
tions and even slight organic contaminants causes its demise. Also, proteins often denature at
BLM-water interfaces and most trans-membrane solute flux measurements are not possible.
A more realistic and rigorous model membrane that could reconstitute integral proteins was
required. This came in the form of spherical lipid bilayer vesicles, more commonly referred to
as 'liposomes'.
Liposomes
The discovery of liposomes is attributed to Alec D. Bangham (
Figure 13.13
) in 1961 (pub-
lished in 1964,
[38]
). For years, Bangham had been working on what he referred to as 'multi-
lamellar smectic mesophases'. The word 'smectic' is derived from the Greek word for soap.
Although smectic mesophases had been observed since the 1930s, it was Bangham who
recognized them for what they were, concentric lipid bilayers, and so initially they were
called Bangosomes. A few years later, Gerald Weissmann changed their name to liposomes,
and it stuck. Alec Bangham is considered to be the 'Father of Liposomes'. It is amazing how
easy it is to prepare multilamellar liposomes. Phospholipids are dissolved in a volatile
organic solvent and transferred to a round-bottom flask. The solvent is evaporated using
nitrogen or argon gas to prevent lipid oxidation. As the flask is rotated during the evapora-
tion process, a thin layer of phospholipid coats the flask's inside wall. The flask is then placed
under a vacuum overnight to eliminate traces of the solvent. An aqueous buffer at a temper-
ature above the phospholipid's melting point (T
m
, Chapter 5) is added to the flask with a few
glass beads to aid in dispersion. As the solution is vortexed, it immediately becomes milky,
indicating the formation of multilamellar liposomes. An electron micrograph of a family of
multilamellar vesicles (MLVs)
is shown in
Figure 13.14
. Depending on the type of
FIGURE 13.14
Electron micrograph of a family of multilamellar vesicles (MLVs) made by the method of
Bangham
[38]
.
