Phase behavior of large unilamellar vesicles composed of synthetic phospholipids

Abstract

Large unilamellar vesicles (LUV) have been prepared by three procedures from several synthetic and natural phosphatidylcholines. Reverse-phase evaporation vesicles (REV) and fusion vesicles were prepared by established procedures. A published procedure for the preparation of dialyzed octyl glucoside vesicles (DOV) was modified to allow its use with synthetic phospholipids. Negative-staining and freeze--fracture electron microscopy was used to determine the vesicle size distribution (mean diameters 800-1000 A) and extent of oligolamellar contamination in DOV preparations. Trapping of 6-carboxyfluorescein yielded measurements of the internal volume (2.6 +/- 0.3 microL/mumol of Pi) consistent with the size distributions determined by electron microscopy. An upper limit of less than 3 mol % oligolamellar vesicle contamination was indicated by calorimetric heat capacity profiles. The phase behaviors of large multilamellar vesicles and all three types of LUV were compared by using high-sensitivity differential scanning calorimetry and fluorescence depolarization of the membrane probe diphenylhexatriene. The most remarkable feature was the increased breadth of the main transition of DOV and of REV relative to the multilamellar species and to fusion vesicles. Both the main transition and the pretransition occurred at nearly the same temperatures in unilamellar and multilamellar species, but the unilamellar pretransition involved less than half the enthalpy observed in the multilamellar transition. Additional experiments indicated that the broadened main phase transition associated with DOV and REV reflected bilayer impurities resulting from preparation. It is concluded that LUV prepared by procedures that avoid impurities undergo a highly cooperative phase transition, as demonstrated here for fusion vesicles.

Different modulation of phospholipase A2 activity by saturated and monounsaturated N-acylethanolamines

“…Laurdan GP values (Fig. 2) show a large decrease at the main phase transition of DPPC LUV (Tm), while it is very hard to assess the presence of the pretransition by the small slope changes shown by GP curves although occurring at a temperature (‫5.63ف‬ЊC), which is similar to previously reported data (39). For this reason, only the gel-to-liquid-crystalline phase transition will be discussed in all samples.…”

“…2A, B). Previous studies demonstrated that DPPC LUVs and multilamellar vesicles (MLVs) have nearly identical phase behavior, with similar pretransition and a main transition (Tm) temperatures (39,40). The gel-to-liquid-crystalline phase transition of DPPC LUVs is known to be highly cooperative (28 and references cited therein).…”

Freeze‐fracture of lipids and model membrane systems

“…The distinction is important because SUVs are usually limit size vesicles and tend to be more unstable than LUVs (Parente and Lentz, 1984;Sheetz and Chan, 1972). A bilayer composed of diacylphospholipids has a minimum radius of curvature around which it can bend.…”

Structure Determination of HIV-1 Tat/Fluid Phase Membranes and DMPC Ripple Phase Using X-Ray Scattering

“…Studies of the ripple phase are normally done on multilamellar systems, but some works have reported the existence of the ripple phase in unilamellar vesicles [40,41]. Most studies have been performed on PCs [1].…”

“…While many studies have used multilamellar samples, the ripple phase has been reported to also exist in large unilamellar vesicles [40,41] and giant unilamellar vesicles (GUVs) [141]. In a GUV composed of a mixture of DPPC and dioleoylphosphatidylcholine (DOPC), coexisting domains of L β and P β have been observed [141].…”