Long-Range Membrane Properties - An Introduction to Biological Membranes - page 224

transition resulted in the enzyme accumulating in the favorable DOPC fluid state domain.
Thus the Ca 2 þ ATPase activity increased.
Direct observations (images) of lipid microdomains have routinely been reported for lipid
monolayers and bilayers using fluorescent probes. It should be pointed out that lipid micro-
domains in model protein-free membranes are orders of magnitude larger than microdo-
mains observed in biological membranes and so are much more amenable to imaging.
A few examples follow:
Figure 11.9 shows epifluorescence images demonstrating simple liquid crystalline/gel
phase separations as a function of lateral pressure on Langmuir Trough lipid monolayers
FIGURE 11.9 Epifluorescence images demonstrating simple liquid crystalline/gel phase separations as
a function of lateral pressure on Langmuir Trough lipid monolayers. Monolayers were made from 70 mol% DPPC
(16:0, 16:0 PC) and 29 mol% SDPC (18:0, 22:6 PC) to which 1 mol% N-rhodamine-PE was added as the membrane
fluorescent imaging agent. Compressions were run and images taken at every 5 mN/m (23 C). Plate 1, 5 mN/m;
Plate 2, 10 mN/m; Plate 3, 15 mN/m; Plate 4, 20 mN/m; Plate 5, 25 mN/m; Plate 6, 30 mN/m. Gel state DPPC
domains appear black while liquid crystalline state SDPC domains appear white [39] .