Kinetics and thermodynamics of the association of dehydroergosterol with lipid bilayer membranes.
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.
Estronca
Luís M B B
LM
Departamento de Química, Universidade de Coimbra, Coimbra, Portugal.
Moreno
Maria João
MJ
Vaz
Winchil L C
WL
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
D045424:Complex Mixtures; D008051:Lipid Bilayers; D010743:Phospholipids; C010905:dehydroergosterol; D004875:Ergosterol