title: A fluorescence anisotropy study on the phase behavior of dimyristoylphosphatidylcholine/cholesterol mixtures.
abstract: The phase behavior of L-alpha-dimyristoylphosphatidylcholine/cholesterol mixtures was studied in multilamellar vesicles by fluorescence polarization of the sterol molecule dehydroergosterol and of the polyene molecule alpha-parinaric acid. In the absence of cholesterol, dehydroergosterol exhibited an increase in polarization as DMPC vesicles were heated through the phase transition. This rise in polarization anisotropy was observed over a 0.6-1.0 degrees C increase in temperature with the midpoint of the phase transition occurring at 23.6 degrees C. Addition of 5 mol% cholesterol completely obliterated this change in polarization anisotropy through the phase transition of DMPC. alpha-Parinaric acid underwent a characteristic decrease in polarization anisotropy through the phase transition of DMPC. The change in anisotropy through the phase transition was over 4-fold greater than the values observed with dehydroergosterol. Vesicles containing 5 mol% cholesterol in the presence of alpha-parinaric acid underwent a decrease in polarization anisotropy that was over 75% of the original decrease in amplitude observed in the absence of any membrane cholesterol. The difference in sensitivity of the two fluorescent probes to the phase transition of DMPC as a function of membrane cholesterol content may be explained by a preferential partitioning of dehydroergosterol (and cholesterol) into a sterol-rich phase at low sterol concentrations. This partitioning allows dehydroergosterol to detect sterol-rich regions in the membrane bilayer.
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002784:Cholesterol; D004134:Dimyristoylphosphatidylcholine; D004875:Ergosterol / Q000031:analogs & derivatives; D005454:Fluorescence Polarization; D008051:Lipid Bilayers; D013050:Spectrometry, Fluorescence
chemical_list: D008051:Lipid Bilayers; C010905:dehydroergosterol; D002784:Cholesterol; D004134:Dimyristoylphosphatidylcholine; D004875:Ergosterol