Binary Bilayer Membrane Research Articles

Phase behavior of binary bilayer membrane of dipalmitoylphosphatidylcholine and stigmasterol

We investigated the phase behavior of a binary bilayer membrane of dipalmitoylphosphatidylcholine (DPPC) and stigmasterol (Stig) as a function of the Stig concentration (XSt) by means of differential scanning calorimetry (DSC) and fluorescence spectroscopy using 6-propionyl-2-(N,N-dimethylamino)naphthalene (Prodan) as a membrane probe. The DSC results revealed that the pretransition and the main transition are abolished at XSt = ca. 0.08 and ca. 0.50, respectively. The main-transition enthalpy (ΔHm) of the DPPC–Stig binary bilayer decreased with XSt in a nonlinear manner, which is contrast to the almost linear decrease in ΔHm for the DPPC–cholesterol (Chol) binary bilayer. This suggests that Stig has a stronger effect of disturbing the chain packing in a gel state and a weaker effect of suppressing the chain melting as compared to Chol. The XSt dependence of the peak width at half height (ΔT1/2) suggests that a drastic change in the phase behavior occurs at XSt = ca. 0.14, which is similar to the DPPC–Chol binary bilayer. The Prodan fluorescence spectra changed depending on the phase state, which was characterized by the wavelength at the emission maximum and allowed us to determine the transition temperatures of the binary bilayers. The compositional phase diagram of the DPPC–Stig binary bilayer was found to be similar to that of the DPPC–Chol binary bilayer. The phase behavior of the DPPC–Stig binary bilayer could be well explained by applying the so-called superlattice view to interpret the phase diagram.

Thermotropic Phase Behavior of Binary Bilayer Membrane of Dipalmitoylphosphatidylcholine and Ergosterol

We investigated the phase behavior of a binary bilayer membrane of dipalmitoylphosphatidylcholine (DPPC) and ergosterol, using Prodan fluorescence spectroscopy and differential scanning calorimetry to construct a temperature–composition phase diagram. We found that several important features of the phase diagram can be explained by the superlattice view, on the basis of the hexagonal lattice, which suggests the presence of a molecular cluster composed of an ergosterol molecule and its six surrounding DPPC molecules above an ergosterol composition of ca. 0.15.

Lateral phase separation in cholesterol/diheptadecanoylphosphatidylcholine binary bilayer membrane

We investigated the phase behavior of cholesterol/diheptadecanoylphosphatidylcholine (C17:0-PC) binary bilayer membrane as a function of the cholesterol composition ( X ch) by fluorescence spectroscopy using 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and differential scanning calorimetry (DSC). The fluorescence spectra showed that the wavelength at the maximum intensity ( λ max) changed depending on the bilayer state: ca. 440 nm for the lamellar gel ( L ′ β or L β) and the liquid ordered (L o) phases and ca. 490 nm for the liquid-crystalline (L α) phase. The transition temperatures were determined from the temperature dependence of λ max and endothermic peaks of the DSC thermograms. Both measurements showed that the pre- and main transition disappear around X ch = 0.05 and 0.30, respectively. The constructed temperature– X ch phase diagram resembled a typical phase diagram for a eutectic binary mixture containing a peritectic point. The presence of a peritectic point at X ch = 0.15 suggested that a complex of cholesterol and C17:0-PC is stoichiometrically formed in the gel phase. Consideration based on the hexagonal lattice model revealed that the compositions of 0.05 and 0.15 correspond to the bilayer states where cholesterol molecules are regularly distributed in different ways. The former is nearly equal to the composition for the membrane occupied entirely with Units (1:18), composed of a cholesterol and 18 surrounding C17:0-PC molecules within the next–next nearest neighbor sites. The latter is represented by a Unit (1:6), including a cholesterol and 6 surrounding C17:0-PC molecules. Further, the disappearance of the main transition at X ch = 0.30 indicates that the pure L o phase can exist in X ch > 0.30. The eutectic behavior observed in the phase diagram was explainable in terms of phase separation between two different types of regions with different types of regular distributions of cholesterol.

A new interpretation of eutectic behavior for distearoylphosphatidylcholine–cholesterol binary bilayer membrane

We investigated the thermotropic phase behavior of the distearoylphosphatidylcholine (DSPC)–cholesterol binary bilayer membrane as a function of the cholesterol composition ( X ch) by fluorescence spectroscopy using 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and differential scanning calorimetry (DSC). The fluorescence spectra, each of which has a single maximum, showed that the wavelength at the maximum intensity ( λ max) changed depending on the bilayer state: ca. 440 nm for the lamellar gel (L β′ or L β) and the liquid ordered (L o) phases, ca. 470 nm for the ripple gel (P β′) phase and ca. 490 nm for the liquid crystalline (L α) phase, respectively. The transition temperatures were determined from the temperature dependences of the λ max and endothermic peaks of the DSC thermograms. Both measurements showed that the pretransition disappears around X ch = 0.035. The constructed temperature– X ch phase diagram indicated that the phase behavior of the binary bilayer membrane at X ch ≤ 0.15 is similar to that of general liquid–solid equilibrium for a binary system where both components are completely miscible in the liquid phase and completely immiscible in the solid phase. It was also revealed that the diagram has two characteristic points: a congruent melting point at X ch = 0.08 and a peritectic-like point at X ch = 0.15. The hexagonal lattice model was used for the interpretation of the phase behavior of the binary bilayer membrane. These characteristic compositions well correspond to the bilayer states in each of which cholesterol molecules are regularly distributed in the hexagonal lattice in a different way. That is, each composition of 0.035, 0.08 and 0.15 is nearly equal to that for the binary bilayer membrane which is entirely occupied with units, each composed of a cholesterol and 30 surrounding DSPC molecules within the next-next-next nearest neighbor sites (Unit (1:30): L β(1:30)), with units, each of a cholesterol and 12 surrounding DSPC molecules within the next nearest sites (Unit (1:12): L β(1:12)) or with units, each of a cholesterol and 6 surrounding DSPC molecules at the nearest neighbor sites (Unit (1:6): L β(1:6)), respectively. Therefore, the eutectic behavior observed in the phase diagram was fully explainable in terms of a kind of phase separation between two different types of regions with different types of regular distributions of cholesterol. Further, the L o phase was found in the higher X ch-region ( X ch > 0.15). No endothermic peak over the temperature range from 10 to 80 °C at X ch = 0.50 suggested that the single L o phase can exist at X ch > 0.50.

1P-217 リン脂質-コレステロール混合二分子膜におけるコレステロール依存性膜結合タンパク質の機能発現(生体膜/人工膜・構造物性,第46回日本生物物理学会年会)

1P-217 リン脂質-コレステロール混合二分子膜におけるコレステロール依存性膜結合タンパク質の機能発現(生体膜/人工膜・構造物性,第46回日本生物物理学会年会)

1P220 高圧蛍光プローブ法によるリン画質-コレステロール混合二分子膜の相挙動の解明(生体膜・人工膜 A) 構造・物性)

1P220 高圧蛍光プローブ法によるリン画質-コレステロール混合二分子膜の相挙動の解明(生体膜・人工膜 A) 構造・物性)

Molecular weight control of photopolymerization at an oriented bilayer surface using phase separation of fluorocarbon- and hydrocarbon-amphiphiles

Binary bilayer membranes composed of a polymerizable hydrocarbon amphiphile and a non-polymerizable fluorocarbon amphiphile form a phase-separated bilayer, and the molecular weight of the polymer produced upon photoinitiation can be controlled by the phase separation of the bilayer.