F. Paltauf

Monolayer characteristics of some 1,2-diacyl, 1-alkyl-2-acyl and 1,2-dialkyl phospholipids at the air-water interface

Abstract Surface pressure and surface potential-molecular area data have been obtained for some 1,2-diacyl, 1-alkyl-2-acyl and 1,2-dialkyl phospholipids at the air-water interface. Replacement of the ester linkages in lecithins by ether links has no significant effect upon the molecular packing in fully expanded or condensed monolayers and only a small effect upon the phase transition from condensed to expanded monolayer. Analogous effects are predicted for lecithins dispersed in excess water. Ether phospholipids have surface potentials which are 30–200 mV lower than those of the corresponding ester compound. This occurs because the carbonyl dipoles play a large role in determining the surface potential of phospholipid monolayers. Estimates are derived for the orientation of the carbonyl groups within the film at various molecular areas. It is concluded that, during the crystallisation of phospholipids in the transitions from expanded to condensed monolayer and liquid crystal to gel phase, the carbonyl groups are forced further out of the plane of the monolayer or bilayer. The biological significance of these findings is discussed.

The inter- and intra-molecular mixing of hydrocarbon chains in lecithin-water systems.

Abstract When pure 1,2 diacyl lecithins containing a different type of hydrocarbon chain in each position of the molecule (intra-molecular chain mixing) are dispersed in excess water, the gel to liquid crystal transition is sharp, as with pure lecithins containing a single type of hydrocarbon chain. The total heat of transition is lower than that observed when the same chain composition is distributed in a mixture of two different lecithins each containing only one type of hydrocarbon chain (inter-molecular mixing). In the latter systems broad transitions are observed, and whenever the experimental temperature is not above that of the transition range clustering of molecules occurs. Bilayers of the isolated lipids of some biological membranes exhibit such clustering at the environmental temperature of the membrane.

Metabolism of the enantiomeric 1-O-alkyl glycerol ethers in the rat intestinal mucosa in vivo; incorporation into 1-O-alkyl and 1-O-alk-1′-enyl glycerol lipids

Abstract 1. 1. The incorporation of orally administered 1-O-(9,10-[ 3 H 2 ] octadecyl ) sn-glycerol and 3-O(1-[ 14 C ] octadecyl ) sn-glycerol into alkyl acyl as well as alk-1′-enyl acyl glycerophosphoryl ethanolamine and alkyl diacyl glycerol of the rat intestinal mucosa was investigated in vivo. 2. 2. The enantiomers were found to be utilized to considerably different extents, the sn-1-isomer being the favored substrate in the above-mentioned biosynthetic reactions. 3. 3. The specific incorporation into alk-1′-enyl glycerol lipids of the 1-O-alkylsn-glycerol as compared to the sn-3-isomer supports the view that the alk-1′-enyl glycerol bond is derived from the alkyl glycerol bond. 4. 4. The amount and chain length distribution of alkyl glycerol ethers naturally occurring in alkyl diacyl glycerols of the rat intestinal mucosa are reported.

The intestinal absorption of 1,2- and 1,3-dialkyl glycerol ethers and of diether phospholipids

Abstract 1. 1. Labeled 1,2- and 1,3-dialkyl glycerol ethers and 1,2-dialkyl analogs of phosphatidyl choline, phosphatidyl ethanolamine and phosphatidic acid were used as model substances for the corresponding fatty acid ester derivatives to study their intestinal absorption and incorporation into lymph lipids. 2. 2. The substances were fed to intact and lymph cannulated rats. Lipids extracted from lymph and organs were analyzed for total activity and distribution of activity between different lipid classes. 3. 3. The amount of dialkyl glycerol ethers absorbed depends on the chain length (8–10%) for the long chain vs. 52% for the dioctyl derivative), but not on the position or degree of saturation of the alkyl moieties. The rate of esterification with fatty acids during passage through the gut, however, is quite different for the 1,2 and 1,3 isomer, the 1,2 isomer being the favored substrate in this reaction. Only traces of intact diether phospholipids are incorporated into lymph lipids. 4. 4. The possibility of ω-oxidation as the pathway for the degradation of the 1,2-dialkyl glycerol ethers is discussed.

Studies on the interaction of cholesterol with diester- and dietherlecithin

The lamellar repeat distances of aqueous dispersions of rac-1,2-dioctadec-9-cis-enyl-glycero-3-phosphorylcholine (dietherlecithin) and 1,2-dioctade-9-cis-enoyl-sn-glycero-3-phosphorylcholine (diesterlecithin) have been measured by X-ray diffraction as a function of water concentration. The point of maximum hydration was found to be 43% (w/w) for dietherlecithin and diesterlecithin respectively; the corresponding lamellar repeat distances being 62.3 å and 60.5 ã. Incorporation of cholesterol above maximum hydration results in the initial increase in the lamellar repeat distance with a maximum around cholesterol concentrations of 25 and 33 mol% for dietherlecithin and die diesterlecithin respectively. The apparent partial specific volumes fo the two lecithins and for lecithin--cholesterol mixtures in sonicated aqueous dispersions were measured. Values of 1.024 cm3-g-1 and 0.987 cm3-g(-1) were obtained for diether- and diesterlecithin, respectively, at 20 degrees C. Diesterlecithin-cholesterol mixtures showed a very small change in partial specific volume while mixtures of dietherlecithin-cholesterol showed a very marked decrease with increasing proportions of cholesterol. From these data a series of structure parameters are derived for the two lecithins and possible implications for the nature of the lecithin-cholesterol interaction are discussed.

An improved synthesis of 1,2-dialkyl glycerol ethers and the synthesis of 14C-labelled trialkyl glycerol ethers.

Abstract A method is described for the preparation of 1,2-dialkyl glycerol ethers starting from 3-tetrahydropyranyl-glycerol and alkyl methanesulfonates. By reaction of an excess of 1,2-dialkyl glycerol ethers and (1- 14 C)-alkyl methanesulfonates 14 C-labelled trialkyl glycerol ethers are obtained in good yields.

Intestinal uptake and metabolism of alkyl acyl glycerophospholipids and of alkyl glycerophospholipids in the rat biosynthesis of plasmalogens from [3H]alkyl glycerophosphoryl [14c]ethanolamine

Abstract 1. 1. In the intestinal mucosa, plasmalogens account for 12% of the phosphatidyl ethanolamine fraction. They are only minor constituents of other phospholipids. 2. 2. The uptake of various radioactively labelled alkyi acyi glycerophospholipids and of the corresponding lyso derivatives into the intestinal mucosa and their conversion to plasmalogens was investigated. 3. 3. [3H]Alkyl acyl glycerophosphoryl choline and -ethanolamine are readily absorbed when administered orally. However, analysis of mucosa lipids revealed that an extensive hydrolytic and oxidative breakdown of the substrates had occurred. After intravenous injection, a preferential uptake by the mucosal cell of the alkyl glycerophospholipids was observed as compared to alkyl acyl glycerophospholipids. The lyso phospholipids were rapidly incorporated into alkyl acyl glycerophospholipids and only minor hydrolytic and oxidative degradation were observed. 4. 4. The highest rate of plasmalogen formation was observed when alkyl glycerophosphoryl ethanolamine was administered. Experiments employing [3H]alkyl glycerophosphoryl [14C]ethanolamine indicated that (a) alkyl glycerophosphoryl ethanolamine is acylated to alkyl acyl glycerophosphoryl ethanolamine prior to incorporation into plasmalogens, (b) no intermediary separation of the alkyl glycerol part and the ethanolamine residue occurred during plasmalogen formation, indicating that the whole alkyl or alkyl acyl glycerophosphoryl ethanolamine unit is converted to the plasmalogen. 5. 5. From the low conversion of alkyl acyl glycerophosphoryl choline, alkyl glycerophosphoryl choline and alkyl acyl glycerophosphate to the corresponding plasmalogens it is concluded that, in the mucosa, plasmalogen formation is specific for ethanolamine-containing alkyl glycerophospholipids.

The intestinal absorption of glycerol trioctadecenyl ether.

Abstract 1. 1. Glycerol tri- cis -9-octadecenyl ether is used as a model substance for triolein in studying the intestinal absorption of non-hydrolysed triglycerides. 2. 2. [ 14 C]Glycerol trioctadecenyl ether was fed to rats provided with a thoracic duct fistula and to non-operated rats. The radioactivity of the lipids of lymph, some organs and the whole carcass was determined. 3. 3. The very poor absorption of [ 14 C]glycerol trioctadecenyl ether confirms the suggestion of others that the absorption of intact triglycerides must be very poor.

Polar group conformation of 1,2-di-O-alkylglycerophosphocholines in the absence and presence of ions

Abstract The conformation of the glycerophosphocholine (GPC) group of various 1,2-di- O -alkyl and 1,2-diacylglycerophosphocholines forming small micelles or single-bilayer vesicles in H 2 O has been studed by NMR in the absence and presence of lanthanide ions. In the absence of lanthanides the motionally averaged polar group conformation of 1,2-di- O -alkylglycerophosphocholine (dialkyl-GPC) is similar to that of the diacyl compound. The replacement of the ester linkages in diacyl phosphatidylcholine by ether bonds has therefore no significant effect on the conformation and segmental motion of the glycerophosphocholine group. This conformation is found to be independent of the state of aggregation, i.e., the main features are the same below and above the critical micellar concentration (CMC). The determining factor must therefore be the intramolecular energetics. Within the experimental accuracy the conformation of dialkyl-GPC in the presence of lanthanide ions is also the same as that of the corresponding diacyl compound. Furthermore, in the presence of lanthanides the polar group conformation of dialkyl-GPC is the same within experimental accuracy in small micelles and single bilayer vesicles. The conformational change induced by lanthanides leads to a reorientation of the OPue5f8N dipole. In the presence of lanthanides the OPue5f8N dipole increases its angle of tilt with respect to the bilayer plane from about 0° (coplanar orientation) to an average inclinication of about 45°. This gives rise to a more extended disposition of the polar group with respect to the bilayer normal.

An improved synthesis of 1-0-[3H] alkyl-2-acyl-sn-glycerol-3-phosphorylethanolamine with an unsaturated acyl chain.

A method is described for the synthesis of 1-0-[9, 10-(3)H2] octadecyl-2-octadecenoyl-sn-glycerol-3-phosphorylethanol-amine, starting from rac 1-0-octadecen-9-ylglycerol. The sn-1-alkyl enantiomer is obtained by an enzymatic reaction involving deacylation of rac 1-0-octadecen-9-yl-2-octadecenoyl-glycerol-3-phosphoryl-N-(tert.-butyloxycarbonyl) ethanolamine with phospholipase A2. The resulting lyso compound is tritiated with 3H2 in the presence of platinum catalyst and reacylated with oleoyl anhydride to yield the final product.