title: A detailed analysis of partial molecular volumes in DPPC/cholesterol binary bilayers.
abstract: We examined the volumetric behavior of the dipalmitoylphosphatidylcholine (DPPC)/cholesterol binary bilayer system with high accuracy and more cholesterol concentrations to reveal the detailed molecular states in the liquid-disordered (Ld) phase, the liquid-ordered (Lo) phase and the gel phase. We measured the average specific volume of the binary bilayer at several temperatures by the neutral flotation method and calculated the average volume per molecule to estimate the partial molecular volumes of DPPC and cholesterol in each phase. As a result, we found that the region with intermediate cholesterol concentrations showed a more complicated behavior than expected from simple coexistence of Ld and Lo domains. We also measured fluorescence decay of trans-parinaric acid (tPA) added into the binary bilayer with more cholesterol concentrations to get further insight into the cholesterol-induced formation of the Lo phase. On the basis of these results we discuss the molecular interaction between DPPC and cholesterol molecule in the Lo phase and the manner of Ld/Lo phase coexistence.
authors.affiliation: Department of Physics, Graduate school of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan. Electronic address: t.miyoshi@kwansei.ac.jp.
authors.forename: Tsubasa
authors.initials: T
authors.lastname: Miyoshi
authors.affiliation: Biochemistry, Department of Bioscience, Åbo Akademi University, Tykistökatu 6A, 20520 Turku, Finland.
authors.forename: Max
authors.initials: M
authors.lastname: Lönnfors
authors.affiliation: Biochemistry, Department of Bioscience, Åbo Akademi University, Tykistökatu 6A, 20520 Turku, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Peter Slotte
authors.affiliation: Department of Physics, Graduate school of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Kato
keywords: Buoyant density measurement; DPPC/cholesterol binary bilayer; Fluorescence decay; L(d)/L(o) phase coexistence; Liquid-ordered phase; Partial molecular volume