Ecy. Yan et Kb. Eisenthal, Effect of cholesterol on molecular transport of organic cations across liposome bilayers probed by second harmonic generation, BIOPHYS J, 79(2), 2000, pp. 898-903
The effect of cholesterol on the molecular transport of an organic cation,
malachite green (MG), across large unilamellar dioleolyphosphatidylglycerol
(DOPG) liposome bilayers with 0-50 mol% cholesterol was studied by second
harmonic generation (SHG), Because SHG is a surface-specific technique, it
requires no labeled molecule, quencher, or shifting agent to distinguish th
e location of the solute molecules. An additional important feature of SHG
is that it is sensitive only to the probe molecules bound to the liposome,
whereas other methods can only differentiate between molecules that are out
side and those inside the liposome, The transport kinetics of MG across the
liposome bilayers was observed in real time, and the results show that cho
lesterol retards the rate of transport of MG across liposome bilayers. The
rate was found to decrease by six times for 50 mol% cholesterol content com
pared with cholesterol-free liposomes. This demonstrates the applicability
of SHG to investigation of the effect of liposome composition on the transp
ort kinetics across the liposome bilayers.