An improved method for the preparation of ‘Mixed-Chain’ phosphatidylethanolamines

Isolation of a phosphatidylserine transfer protein from yeast cytosol

A phospholipid transfer protein with a broad substrate specificity was isolated from yeast cytosol. The rate of transfer catalyzed by this protein in vitro is highest for phosphatidylserine; phosphatidylethanolamine, cardiolipin, phosphatidic acid and ergosterol are transported at a lower rate. In contrast to the yeast phosphatidylinositol transfer protein (Daum, G. and Paltauf, F. (1984) Biochim. Biophys. Acta 794, 385-391) the phosphatidylserine transfer protein does not catalyze the translocation of phosphatidylinositol or phosphatidylcholine. Using chromatographic methods the phosphatidylserine transfer protein was enriched approximately 3000-fold over yeast cytosol. The protein is inactivated by heat, detergents and proteinases. Divalent cations strongly inhibit the transfer of phosphatidylserine in vitro, and EDTA at low concentrations has a stimulatory effect.

Stabilization of non-bilayer structures by the etherlipid ethanolamine plasmalogen

The thermotropic phase behavior of mixtures between diradylphosphatidylethanolamines and diacylphosphatidylcholine was studied using polarized light microscopy, 31P-NMR spectroscopy and synchrotron X-ray diffraction. Multilamellar liposomes composed of alkenylacylphosphatidylethanolamine (ethanolamine plasmalogen) undergo a phase transition from a lamellar to an inverse hexagonal lipid structure at 30 degrees C, which is about 20 degrees C and 30 degrees C lower as compared to its alkylacyl- and diacyl-analog, respectively. These results indicate a higher affinity to non-bilayer structures for the ether lipids. In the presence of the bilayer stabilizing phospholipid, palmitoyloleoylphosphatidylcholine, the transition is shifted to higher temperature without any significant changes in the overall structural parameters as revealed by X-ray diffraction experiments. Again, ethanolamine plasmalogen stabilizes the inverted hexagonal phase to the highest extent, i.e. even in the presence of 40 mol% palmitoyloleoylphosphatidylcholine a pure inverse hexagonal phase is formed at 60 degrees C. Such a result was not reported so far for a diacylphosphatidylethanolamine. This property of ethanolamine plasmalogen might be predominantly explained by an optimized packing of the hydrocarbon chains in the corners and interface region of the hexagonal tubes, owing to a different conformation of the sn-2 chain, which was deduced from 2H-NMR experiments (Malthaner, M., Hermetter, A., Paltauf, F. and Seelig, J. (1987) Biochim. Biophys. Acta 900, 191-197). Data obtained by time resolved X-ray diffraction show a coexistence of lamellar and inverse hexagonal structures in the phase transition region, but do not indicate the existence of non-lamellar intermediates or disorder within the sensitivity limits of the method.

Membrane properties modulate the activity of a phosphatidylinositol transfer protein from the yeast, Saccharomyces cerevisiae

A phospholipid transfer protein from yeast (Daum, G. and Paltauf, F. (1984) Biochim. Biophys. Acta 794, 385-391) was 2800-fold enriched by an improved procedure. The specificity of this transfer protein and the influence of membrane properties of acceptor vesicles (lipid composition, charge, fluidity) on the transfer activity were determined in vitro using pyrene-labeled phospholipids. The yeast transfer protein forms a complex with phosphatidylinositol or phosphatidylcholine, respectively, and transfers these two phospholipids between biological and/or artificial membranes. The transfer rate for phosphatidylinositol is 19-fold higher than for phosphatidylcholine as determined with 1:8 mixtures of phosphatidylinositol and phosphatidylcholine in donor and acceptor membrane vesicles. If acceptor membranes consist only of non-transferable phospholipids, e.g., phosphatidylethanolamine, a moderate but significant net transfer of phosphatidylcholine occurs. Phosphatidylcholine transfer is inhibited to a variable extent by negatively charged phospholipids and by fatty acids. Differences in the accessibility of the charged groups of lipids to the transfer protein might account for the different inhibitory effects, which occur in the order phosphatidylserine which is greater than phosphatidylglycerol which is greater than phosphatidylinositol which is greater than cardiolipin which is greater than phosphatidic acid which is greater than fatty acids. Although mitochondrial membranes contain high amounts of negatively charged phospholipids, they serve effectively as acceptor membranes, whereas transfer to vesicles prepared from total mitochondrial lipids is essentially zero. Ergosterol reduces the transfer rate, probably by decreasing membrane fluidity. This notion is supported by data obtained with dipalmitoyl phosphatidylcholine as acceptor vesicle component; in this case the transfer rate is significantly reduced below the phase transition temperature of the phospholipid.

Influence of plasmalogen deficiency on membrane fluidity of human skin fibroblasts: a fluorescence anisotropy study

The influence of plasmalogen deficiency on membrane lipid mobility was determined by measuring fluorescence anisotropy of trimethylammoniumdiphenylhexatriene (TMA-DPH) and diphenylhexatrienylpropanoylhydrazylstachyose (glyco-DPH) inserted in the plasma membranes of human skin fibroblasts deficient in plasmalogens. The cells used were from patients affected with cerebrohepatorenal (Zellweger) syndrome (CHRS) or rhizomelic chondrodysplasia punctata. Their plasmalogen content (0-5% of total phospholipid) is significantly reduced compared with that of control cells from healthy donors (13-15% of total phospholipid) or of CHRS fibroblasts supplemented with the plasmalogen precursor, hexadecylglycerol. Plasmalogen-deficient cells consistently showed lower fluorescence anisotropies of membrane-bound DPH fluorophores corresponding to higher membrane lipid mobilities as compared to controls. However, very similar lipid mobilities were found for sonicated aqueous dispersions of phospholipids extracted either from CHRS or control cells. Therefore, the differences observed with living cells are not due to differences in the overall physical properties of the membrane lipid constituents. Other phenomena such as lipid asymmetry and/or plasmalogen-protein interactions may be responsible for the effects observed in the biomembranes.