title: Cholesterol-phospholipid association in fluid bilayers: a thermodynamic analysis from nearest-neighbor recognition measurements.
abstract: The mixing behavior of exchangeable, disulfide-based mimics of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol has been examined as a function of temperature in host membranes made from DPPC and cholesterol in the liquid-disordered phase (ld), in the liquid-ordered phase (lo), and in the liquid-disordered/liquid-ordered coexistence region (ld/lo). In the ld region, lipid mixing was found to be temperature insensitive, reflecting close to ideal behavior. In contrast, a significant temperature dependence was observed in the lo phase from 45 to 60 degrees C, when 35 or 40 mol % sterol was present. In this region, sterol-phospholipid association was characterized by DeltaHo = -2.06 +/- 0.14 kcal/mol of phospholipid and DeltaS degrees = -4.48 +/- 0.44 cal/K mol of phospholipid. From 60 to 65 degrees C, the mixing of these lipids was found to be insensitive to temperature, and sterol-phospholipid association was now entropy driven; that is, DeltaHo = -0.23 +/- 0.38 kcal/mol of phospholipid and DeltaS degrees = +1.68 +/- 1.12 cal/K mol of phospholipid. In the liquid-disordered/liquid-ordered coexistence region, changes in lipid mixing reflect changes in the phase composition of the membrane.
authors.affiliation: Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, USA.
authors.forename: Jianbing
authors.initials: J
authors.lastname: Zhang
authors.forename: Honghua
authors.initials: H
authors.lastname: Cao
authors.forename: Bingwen
authors.initials: B
authors.lastname: Jing
authors.forename: Paulo F
authors.initials: PF
authors.lastname: Almeida
authors.forename: Steven L
authors.initials: SL
authors.lastname: Regen
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000032:analysis / Q000737:chemistry*; D002784:Cholesterol / Q000032:analysis / Q000737:chemistry*; D045424:Complex Mixtures / Q000032:analysis / Q000737:chemistry; D003198:Computer Simulation; D008051:Lipid Bilayers / Q000032:analysis / Q000737:chemistry*; D046911:Macromolecular Substances / Q000032:analysis / Q000737:chemistry; D008560:Membrane Fluidity; D008956:Models, Chemical; D008958:Models, Molecular; D044367:Phase Transition; D013816:Thermodynamics
chemical_list: D045424:Complex Mixtures; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D015060:1,2-Dipalmitoylphosphatidylcholine; D002784:Cholesterol