Miscibility gap in fluid dimyristoylphosphatidylcholine:cholesterol as "seen" by x rays.
A binary mixture of dimyristoylphosphatidylcholine (DMPC) and cholesterol displays a fluid miscibility gap under excess water conditions. Effects due to the imperfect miscibility of the two amphiphiles are studied near to and far from thermodynamic equilibrium by time-resolved small angle x-ray diffraction. The experiment discloses that this mixture phase separates when leaving the miscibility gap upon heating, a transition that is not included in current phase diagrams. This transition appears to be reversible and shows a temperature hysteresis of only a few degrees. We suggest a model in which the transition is driven with increasing temperature by a movement of the cholesterol away from the hydrophilic-hydrophobic interface toward the hydrophobic core of the bilayer.
Richter
F
F
European Molecular Biology Laboratory at DESY, Notkestrasse 85, D-22603 Hamburg, Germany. efrichter@web.de
Rapp
G
G
Finegold
L
L
D055592:Biophysical Phenomena; D001703:Biophysics; D002784:Cholesterol / Q000737:chemistry*; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D019277:Entropy; D015233:Models, Statistical; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors; D014961:X-Ray Diffraction; D014965:X-Rays
D002784:Cholesterol; D004134:Dimyristoylphosphatidylcholine