Lipid polymorphism and the functional roles of lipids in biological membranes

Further aspects of the Ca2+-dependent polymorphism of bovine heart cardiolipin

“…1B and 1C). In the presence of a molar excess of Ca 2÷ the lineshape typical of lipids in the hexagonal H n phase [29] with a reversed asymmetry and reduced width is observed (Fig. 1D).…”

“…Liposomes prepared from the sodium salt of cardiolipin are organized in extended bilayers as evidenced by the characteristic asymmetrical 31p_ NMR lineshape with a low-field shoulder and a high-field peak [29] separated by approx. 32 ppm (Fig.…”

Correlation between molecular shape and hexagonal HII phase promoting ability of sterols

“…Also incorporation of the 3-ketosteroids into erythrocytes greatly increases the permeability and fragility of the membrane [8] which might be related to their strong bilayer-destabilizing effect. In [9] a correlation was proposed between the molecular shape and the phase preference of lipid molecules. Lipids with a small polar head group and a relatively large hydrocarbon area are 'coneshape' and thus prefer to organize themselves into inverted structures such as the hexagonal HJJ phase or inverted micelles.…”

“…A relationship between these structural characteristics and membrane permeabilities is observed in pure lecithin liposomes [5] and also in biological membrane systems [6-81. Nothing is known about the effect of sterol structure on the phase preference of lipids. Therefore, we have investigated by 3'P NMR the effect of different sterols on the bilayer + hexagonal HII transition [9] [14]. Sterols were purchased from the following commercial sources: .…”

“…Proton-decoupled 36.4 MHz 31P NMR spectra were obtained as in [lo]. The % of lipid organized in extended bilayers or hexagonal Htt phases were determined by computer subtraction methods, using the characteristic pure 'bilayer' and 'hexagonal' types of 3'P NMR line shape [9] as references. In no case were isotropic 3'P NMR signals observed.…”