Showing papers on "Phosphatidylethanolamine published in 1976"

Location of phosphatidylethanolamine and phosphatidylserine in the human platelet plasma membrane.

Abstract: The location of phospholipids in the human platelet plasma membrane was probed with 2, 4, 6-trinitrobenzenesulfonate (TNBS). TNBS does not penetrate inintact cells and can label phosphatidylethanolamine (PE) and phosphatidylserine (PS). In tact platelets, PE is not accessible to TNBS during the initial 15 min. However, 6.9% PE reacts with TNBS after 30 min and 17.9% PE is labeled after 90 min. In intact platelets, PS is not labeled even after 2 h. In contrast, in phospholipids extracted from platelets 71% PE and 26.5% PS react with TNBS within 5 min. This indicates that PS is inaccessible and PE is relatively inaccessible to TNBS in intact platelets. After incubation of platelets with thrombin, there is increased labeling of PE but no labeling of PS. The incubation of platelets with thrombin (0.05 U/ml) for 5 min results in 16.2% increase of PE labeling during subsequent 30-min incubation with TNBS. PS does not appear to be a component of the functional surface of platelets. However, exposure of PE may have a critical role in platelet hemostatic function. The implication of the study is that there is asymmetry of phopholipids in the platelet plasma membrane which has considerable physiological significance.

Transbilayer phospholipid asymmetry and its maintenance in the membrane of influenza virus.

Abstract: Two phospholipid exchange proteins and two phospholipases C have been employed to determine the phospholipid composition of the outer surface of the membrane of influenza virus. These four protein probes have defined the same accessible and inaccessible pool for each viral phospholipid. Phospholipids which are exchangeable or hydrolyzable are located on the outer surface, whereas the inaccessible pool is located at the inner surface of the viral bilayer. The two pools are unequal in size, with ca. 30% of the total phospholipid accessible to the four proteins, and ca. 70% inaccessible. The membrane is thus highly asymmetric with regard to the amount of phospholipid on each side of the membrane. There is also a marked asymmetry of phospholipid composition. Phosphatidylcholine and phosphatidylinositol are enriched in the outer surface, and sphingomyelim is enriched in the inner surface, whereas phosphatidylethanolamine and phosphatidylserine are present in similar proportions in each surface. This distribution is qualitatively different from that previously reported for the human erythrocyte. The close agreement between results obtained with excahnge proteins and phospholipases C demonstrates that the hydrolytic action of these enzymes does not alter phospholipid asymmetry. The nonperturbing nature of the exchange proteins has permitted the rate of transmembrane movement of phospholipids (flip-flop) in the intact virion to be studied. This process could not be detected after 2 days at 37 degrees C. It was estimated that the half-time for flip-flop is indeterminately in excess of 30 days for sphingomyelin and 10 days for phosphatidylcholine at 37 degrees C. These extremely long times provide a simple explanation for the maintenance of transbilayer asymmetry in influenza virions and possibly, other membranes. Since the viral membrane is acquired by budding through the host cell plasma membrane, the transbilayer distribution of phospholipids observed in the virions presumably reflects a similar asymmetric distribution of phospholipids in the host cell surface membrane. Because animal cells in culture do not incorporate extracellular phospholipid, our results demonstrate that individual cells have the capacity to generate asymmetric membranes.

Phosphatidylcholine Synthesis in Castor Bean Endosperm

Abstract: Three pathways for phosphatidylcholine synthesis were assayed in castor bean (Ricinus communis var. Hale) endosperm. Phosphatidylethanolamine: S-adenosylmethionine methyl transferase occurred predominantly in the endoplasmic reticulum fraction, but some activity appeared in the mitochondria. Phosphorylcholine glyceride transferase occurred exclusively in the endoplasmic reticulum. The phosphorylcholine glyceride transferase activity was approximately 20-fold greater than the methylation pathway in the endoplasmic reticulum. No exchange activity was found. The Michaelis constant for the methylation was 31 mum for S-adenosylmethionine; phosphatidylethanolamine promoted the reaction slightly while other intermediates stimulated it by about 50%. The pH optimum was 9. Phosphorylcholine glyceride transferase had a Michaelis constant of 9.7 mum for cytidine diphosphate choline but variable results were obtained from diglycerides. The pH optimum was 7.5 and a divalent cation was required, Mg(2+) giving the greatest stimulation.

Phospholipid and lipopolysaccharide in Proteus mirabilis and its stable protoplast L-form. Difference in content and fatty acid composition.

Abstract: Cells of the stable, protoplast L-form of Proteus mirabilis contain 1.5 to 2 times more extractable lipid, mostly phospholipid, per dry weight than cells of the bacterial form. Under identical conditions of cultivation the qualitative and quantitative composition of the phospholipid is very similar in both cell forms. The range of mole percentages of individual phospholipid species is 76–80 for phosphatidylethanolamine, 10–13 for phosphatidylglycerol, 3.9–5.5 for diphosphatidylglycerol and 1.0–2.1 for lysophospholipid. However, all phospholipid species in the L-form differ from those of the bacterial form by a lower content of long-chain fatty acids and a higher content of short-chain fatty acids. Growth of the L-form in the presence of growth-stimulating horse serum results in a change of phospholipid composition accompanied by the uptake of phosphotipid and fatty acids from the serum into L-form phospholipid. L-form protoplasts synthesize the same two types of Lipopolysaccharide, I and II, that were previously identified in the bacterial form of Proteus mirabilis. However, only small amounts of the more hydrophilic lipopolysaccharide II are present in the L-form. Lipopolysaccharides from both cell forms have virtually identical polysaccharide compositions but differ strikingly in the relative content of fatty acids in their lipid-A moieties. Molar ratios of tetradecanoic acid, hexadecanoic acid and 3-hydroxytetradecanoic acid are 5:1:6 in the bacterial form and 5:0.1:6 in the L-form grown in serum-free medium. The observed differences between the bacterial form and the protoplast L-form are interpreted as results of the adaptation of the L-form to life in the state lacking an envelope by formation of a physically more stable but still sufficiently fluid protoplast membrane. A rapid method based on fatty acid analysis for the simultaneous quantitative determination of phospholipid and lipopolysaccharide content of whole cells is reported.

Polar-group behaviour in mixed monolayers of phospholipids and fusogenic lipids.

Abstract: 1. The surface potentials of mixed monolayers of synthetic phospholipids with lipids that are fusogenic for hen erythrocytes were investigated. 2. At pH 5.6 and 10, but not at pH2, mixed monolayers of the fusogenic lipid, glycerol mono-oleate, with phosphatidylcholine exhibited negative deviations from the ideality rule in surface potential per molecule which were accompanied by negative deviations in mean molecular area. 3. Interactions of this type were not seen with chemically related but non-fusogenic lipids, nor were they found in mixed monolayers of any of the lipids with phosphatidylethanolamine. 4. Experiments with dihexadecyl phosphate and hexadecyltrimethyl-ammonium indicated that the complete head group of phosphatidylcholine is required for its observed behaviour with fusogenic lipids. 5. Bivalent cations (Ca2+, UO2(2+) or Zn2+) in the subphase at pH 5.6 significantly modified the behaviour of mixed monolayers of fusogenic lipids with phospholipids; there was a parallel perturbing effect of fusogenic lipids on interactions between monolayers of phospholipids and bivalent cations. 6. Possible molecular interactions of fusogenic lipids with membrane phospholipids, and the role of Ca2+, are discussed which may be relevant to cell fusion in erythrocytes induced by low-melting lipids in the presence of Ca2+.

Arachidonic acid release from diacyl phosphatidylethanolamine by human platelet membranes.

Abstract: At pH9.5 in the presence of 10 mM-Ca2+, human platelet membranes released 22% (167 of 785 nmol) of arachidonic acid that was esterified to phospholipids. With the use of synthetic choline (dinonadecanoyl) and ethanolamine (diheptadecanoyl) phosphoglycerides as internal reference compounds, 115 nmol of the released arachidonic acid was shown to be derived from endogenous breakdown of the phosphatidylethanolamine fraction. Further, the lysophosphatidylethanolamine that was released along with the arachidonic acid was shown virtually to lack fatty aldehydes and to contain a preponderance of fatty acids that have a preference for esterification at the 1-position of naturally occurring phosphatidylethanolamine of human platelets. These findings ruled out plasmalogen phosphatidylethanolamine as the source of the released arachidonic acid. We conclude that diacyl phosphatidylethanolamine was the principal source of arachidonic acid released by human platelet membranes under the conditions described.

The Protein‐Mediated Transfer of Phosphatidylcholine between Membranes

Abstract: The phosphatidylcholine exchange protein from bovine liver catalyzes the transfer of phosphatidylcholine between rat liver mitochondria and sonicated liposomes. The effect of changes in the liposomal lipid composition and ionic composition of the medium on the transfer have been determined. In addition, it has been determined how these changes affected the electrophoretic mobility i.e. the surface charge of the membrane particles involved. Transfer was inhibited by the incorporation of negatively charged phosphatidic acid, phosphatidylserine, phosphatidylglycerol and phosphatidylinositol into the phosphatidylcholine-containing vesicles; zwitterionic phosphatidylethanolamine had much less of an inhibitory effect while positively charged stearylamine stimulated. The cation Mg 2+and, to a lesser extent, K+ overcame the inhibitory effect exerted by phosphatidic acid, in that concentration range where these ions neutralized the negative surface charge most effectively. Under conditions where Mg2+ and K+ affected the membrane surface charge relatively little inhibition was observed. In measuring the protein-mediated transfer between a monolayer and vesicles consisting of only phosphatidylcholine, cations inhibited the transfer in the order Las3+ < Mg2+≤ Ca2+≤ K+= Na+. Inhibition was not related to the ionic strength, and very likely reflects an interference of these cations with an electrostatic interaction between the exchange protein and the polar head group of phosphatidylcholine

The Use of Phospholipases in the Determination of Asymmetric Phospholipid Distribution in Membranes

Abstract: Specific information on the localization of components in the membrane is a necessary prerequisite to understanding the molecular organization and function of biological membranes. In the last decade, variety of techniques have been developed that provide information on the organization of membrane constituents. For example, various investigators have shown that several proteins may occupy different locations in the red cell membrane (for recent reviews, see Wallach, 1972 and Juliano, 1973), and a nonrandom distribution of phospholipids between the exterior and interior sides of the erythrocyte membrane was proposed by Bretscher (1972, 1973) [based on the observation that the relatively nonpermeant reagent formylmethionyl-sulfone methylphosphate (FMMP) failed to react with phosphatidylethanolamine and phosphatidylserine of intact cells]. These observations of Bretscher were essentially confirmed by Gordeski and Marinetti (1973). They used the nonpenetrating probe, 2,4,6-trinitrobenzene-sulfonate, although they could label some of the phosphatidylethanolamine of intact cells. Since both these reagents are intrinsically unable to react with cholinecontaining phospholipids, these results should be taken only as indirect evidence that lecithin and sphingomyelin form the outer monolayer of the erythrocyte membrane.