title: Kinetics and thermodynamics of the association of dehydroergosterol with lipid bilayer membranes.
abstract: We have examined the detailed kinetics and thermodynamics of the association of Ergosta-5,7,9(11),22-tetraen-3beta-ol (dehydroergosterol, DHE) with lipid bilayers prepared from 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), a 1:1 binary mixture of POPC and cholesterol (Chol), and a 6:4 binary mixture of egg sphingomyelin (SpM) and Chol. Association of DHE with all three membranes was shown to be entropically driven, most so in the case of SpM-Chol bilayers. Equilibrium partition coefficients for partitioning of DHE between the lipid phase and the aqueous phase were shown to be similar for POPC and POPC-Chol bilayers between 15 and 35 degrees C. Partitioning into the SpM-Chol bilayer is favored at higher temperatures and there is a crossover in solubility preference at approximately 25 degrees C. Insertion (k(+)) and desorption (k(-)) rate constants were shown to be very similar for POPC and POPC-Chol bilayer membranes, but were lower for SpM-Chol bilayers. Similar results were previously reported by us for the association of other amphiphiles with these membranes. We propose a model for the microscopic structure of a POPC-Chol (1:1) bilayer membrane that is consistent with these observations.
authors.affiliation: Departamento de Química, Universidade de Coimbra, Coimbra, Portugal.
authors.forename: Luís M B B
authors.initials: LM
authors.lastname: Estronca
authors.forename: Maria João
authors.initials: MJ
authors.lastname: Moreno
authors.forename: Winchil L C
authors.initials: WL
authors.lastname: Vaz
mesh_terms: D045424:Complex Mixtures / Q000737:chemistry; D004735:Energy Transfer; D004875:Ergosterol / Q000031:analogs & derivatives* / Q000737:chemistry; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D008560:Membrane Fluidity; D008968:Molecular Conformation; D044367:Phase Transition; D010743:Phospholipids / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D045424:Complex Mixtures; D008051:Lipid Bilayers; D010743:Phospholipids; C010905:dehydroergosterol; D004875:Ergosterol