title: The relationship between compositional phase separation and vesicle morphology: implications for the regulation of phospholipase A2 by membrane structure.
abstract: The action of phospholipase A2 (PLA2) on bilayer substrates causes the accumulation of reaction products, lyso-phospholipid and fatty acid. These reaction products and the phospholipid substrate generate compositional heterogeneities and then apparently phase separate when a critical mole fraction of reaction product accumulates in the membrane. This putative phase separation drives an abrupt morphologic rearrangement of the vesicle, which may be in turn responsible for modulating the activity of PLA2. Here we examine the thermotropic properties of the phase-separated lipid system formed upon hydrating colyophilized reaction products (1:1 palmitic acid:1-palmitoyl-2-lyso-phosphatidylcholine) and substrate, dipalmitoylphosphatidylcholine. The mixture forms structures which are not canonical spherical vesicles and appear to be disks in the gel-state. The main gel-liquid transition of these structures is hysteretic. This hysteresis is apparent using several techniques, each selected for its sensitivity to different aspects of a lipid aggregate's structure. The thermotropic hysteresis reflects the coupling between phase separation and changes in vesicle morphology.
authors.affiliation: Department of Biochemistry, University of Virginia Health Sciences Center, Charlottesville 22908, USA.
authors.forename: W R
authors.initials: WR
authors.lastname: Burack
authors.forename: A R
authors.initials: AR
authors.lastname: Dibble
authors.forename: R L
authors.initials: RL
authors.lastname: Biltonen
mesh_terms: D008027:Light; D008051:Lipid Bilayers / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008563:Membrane Lipids / Q000378:metabolism*; D008567:Membranes, Artificial; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D012542:Scattering, Radiation; D013816:Thermodynamics
chemical_list: D008051:Lipid Bilayers; D008563:Membrane Lipids; D008567:Membranes, Artificial; D010741:Phospholipases A; D054467:Phospholipases A2