title: [Fluorometric analysis of liquid-crystalline to inverted hexagonal phase transition induced by diacylglycerol in liposomes].
abstract: In order to delineate the physiological role of diacylglycerol (DAG) to induce phase transition from liquid-crystalline (L alpha) to inverted hexagonal (HII) phase, the minimal concentration of dioleoylglycerol (DOG) required for the initiation of the phase transition was determined by the fluorescence spectroscopy using multi-lamellar vesicles composed of brain phosphatidylcholine (PC), brain phosphatidylethanolamine (PE) and cholesterol (CHOL) = 1:1:1 (mol/mol). DOG reduced the initial temperature of the phase transition at the constant rate of 5.6 degrees C per mol% of DOG and required 1.6 mol% of total lipids for the initial induction of the HII phase in pH 7.4 at 37 degrees C. This suggested that physiological concentration of DAG may induce L alpha to HII phase transition in biomembranes. The molecular motion of lipids in the phase transition was analysed by means of time-resolved fluorescence depolarization spectroscopy using fluorescence-labelled lipids in the same liposomes. Wobbling angle of fluorescence probes increased at the acyl-chain of phospholipid and decreased at the head group in the DOG-induced L alpha to HII phase transition. This corresponds the negative change of mean curvature of the membrane in the phase transition. Wobbling angle of fluorescence probes, 1,6-phenyl-trans-1,3,5-hexatriene (DPH), at the acyl-chain was larger in DPH-glycerol (G) than DPH-phosphatidic acid (PA) and DPH-PC, which suggested that the mobility of the acyl-chain of DAG may be greater than that of PC and PA.
authors.affiliation: Second Department of Biochemistry, Hokkaido University School of Medicine, Sapporo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Naganuma
mesh_terms: D003460:Crystallization; D004075:Diglycerides / Q000494:pharmacology*; D008081:Liposomes / Q000737:chemistry; D008563:Membrane Lipids / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry; D010714:Phosphatidylethanolamines / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D004075:Diglycerides; D008081:Liposomes; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines