Phase equilibriums in binary mixtures of dimyristoylphosphatidylcholine and cardiolipin

Abstract

Paramagnetic resonance spectra of the spin-label 2,2,6,6-tetramethylpiperidinyl-l-oxy have been used to study phase separations in binary mixtures of dimyristoyl-phosphatidylcholine and cardiolipin. Two different samples of cardiolipin were used: (i) One sample contained calcium ions at a mole ratio of calcium:cardiolipin = 1:2; the experimental data support the view that cardiolipin is present in the bilayer membrane as calcium ion linked dimers, (CL)2 Ca2+. (ii) A calcium-free sodium cardiolipin sample yielded remarkable spin-label partition data that were quite different from those obtained in the presence of Ca2+. In both cases the spin-label data provide evidence for compound formation and for fluid-fluid immiscibility in the bilayer membrane.

Evidence for superlattice arrangements in fluid phosphatidylcholine/phosphatidylethanolamine bilayers

“…Headgroup superlattices could form in bilayers containing two phospholipids that differ significantly in the steric properties of their polar headgroups or when one of the species carries a net charge. In fact, the formation of stoichiometric complexes, or compounds, observed previously in various mixed lipid bior monolayer systems (Berclaz and McConnell, 1981;Cunningham et al, 1989;Heimburg et al, 1992;Swamy et al, 1995;Dibble et al, 1996), could be interpreted as formation of headgroup superlattices in those systems.…”

Evidence for phospholipid microdomain formation in liquid crystalline liposomes reconstituted with Escherichia coli lactose permease

“…Formation of lipid domains in liquid crystalline bilayers, resulting from the mismatch of the effective lengths of the hydrophobic parts of the constituent phospholipids, has recently been described (Lehtonen et al, 1996). To this end, there is experimental evidence revealing organization of fluid binary lipid mixtures into regular superlattice arrays (Berclaz and McConnell, 1981;Somerharju et al, 1985; Kinnunen et al, 1987;Tang and Chong, 1992;Chong et al, 1994;Tang et al, 1995).…”

E/M dips. Evidence for lipids regularly distributed into hexagonal super-lattices in pyrene-PC/DMPC binary mixtures at specific concentrations

“…The components of binary mixtures of lipids can be either phase separated, randomly distributed, or regularly distributed (Von Dreele, 1978). Information on lipid lateral distribution can be deduced from freeze-etch electron microscopy (e.g., Tillack et al, 1982;, fluorescence microscopy (e.g., Haverstick and Glaser, 1987; Rodgers and Glaser, 1991), calorimetry (e.g., Mabrey et al, 1978;Melchior, 1986), spin labels (e.g., Berclaz and McConnell, 1981), the thiolate-disulfide interchange method (Krisovitch and Regen, 1991), and computer simulations (e.g., Jan et al, 1984).…”