Long-Range Membrane Properties - An Introduction to Biological Membranes - page 227

FIGURE 11.12 Schematic diagram of an atomic force microscope (AFM) [43] .
surface height is exactly what AFM is best suited for [45] . As a result, by AFM the top of rafts
appear lighter (they are higher) than the thinner and thus lower membrane domains.
Figure 11.13 shows an example of lipid raft microdomains imaged by AFM. A mica-
supported lipid bilayer was made from equimolar DOPC (18:1,18:1 PC) and brain SM to
which the GPI-anchored protein placental alkaline phosphatase (PLAP) was added [46] .
SM-rich lipid rafts are in gray and protrude above the black, DOPC-rich, non-raft domains
by ~7 ˚ . PLAP are white spikes. The image demonstrates that PLAP is almost exclusively
found in rafts.
Before the advent of AFM, lipid rafts had historically been imaged by fluorescence micros-
copy of raft-associated gangliosides that bind fluorescent cholera toxin [46] . Model bilayer
FIGURE 11.13 AFM image of lipid bilayer membrane composed of equimolar DOPC and brain SM to which
the GPI-anchored protein placental alkaline phosphatase (PLAP) is added [46] . SM-rich lipid rafts are in gray, the
DOPC-rich non-rafts in black, and PLAP are white spikes. The image demonstrates that PLAP is almost exclusively
found in rafts. The width of the scan is ~2 m m [45] .