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Biomedical subjects

J de Gier

Publications and source records attributed to J de Gier.

At least 55 records · Page 3Linked to original sources
PubMed1980

Association of lysophosphatidylcholine with fatty acids in aqueous phase to form bilayers.

Lysophospholipids have been implicated in a variety of physiological process. In vivo lysophospholipids are invariably produced with fatty acids as the product of hydrolysis by phospholipase A2 (ref. 2). Therefore, it is of considerable interest to examine the properties of the mixture of these lipids in aqueous suspensions. Results presented here demonstrate that a mixture of fatty acid and lysophosphatidylcholine forms a bilayer type of organisation even though the individual components form micelles when dispersed in an aqueous phase.

Chemical Phenomena↗
PubMed1980

Differential miscibility properties of various phosphatidylcholine/lysophosphatidylcholine mixtures.

Using enthalphy data from differential scanning calorimetry experiments and 13C-NMR linewidths of specifically (N-Me-13C)-labelled lipids, the miscibility properties of phosphatidylcholines and lysophosphatidylcholines in liposomal dispersons have been investigated. It was found that 16 : 0 lysophosphatidylcholine mixes homogeneously in 16 : 0/16 : 0 phosphatidylcholine bilayers. Mixtures of 16 : 0 lysophosphatidylcholine with 18 : 1c/18 : 1c phosphatidylcholine, of 18 : 1c lysophosphatidylcholine with 16 : 0/16 : 0 phosphatidylcholine and of 18 : 1c lysophosphatidylcholine with 18 : 1c/18 : 1c phosphatidylcholine of exhibited immiscibility in the phosphatidylcholine gel state.

Calorimetry, Differential Scanning↗
PubMed1980

Barrier characteristics of membrane model systems containing unsaturated phosphatidylethanolamines.

The barrier characteristics of membrane model systems containing unsaturated phosphatidylethanolamines have been investigated. (1) At increasing temperatures 18:1c/18:lc-phosphatidylethanolamine liposomes lose their permeability barrier for K+ as a consequence of the transition from a lamellar to a hexagonal orientation as detected by 31P-NMR and freeze-fracturing electron microscopy. (2) Introduction of 18:1c/18:1c-phosphatidylcholine in the 18:1c/18:1c-phosphatidylethanolamine lipid system stabilizes the bilayer structure and the permeability barrier for K+ and glucose while cholesterol destabilizes. (3) Upon heating of the investigated 18:1c/18:1c-phosphatidylcholine-18:1c/18:1c-phosphatidylethanolamine-(cholesterol) mixtures, structures are formed which give rise to isotropic 31P-NMR signals and which on the basis of freeze-fracture pictures are interpreted as sponge-like structures. Lowering the temperature results in restoration of the barrier function of the lipid structures.

Freeze Fracturing↗
PubMed1979

The occurrence of lipidic particles in lipid bilayers as seen by 31P NMR and freeze-fracture electron-microscopy.

A new type of lipid organization is observed in mixtures of phosphatidyl-choline with cardiolipin (in the presence of Ca2+), monoglycosyldiglyceride and phosphatidylethanolamine (in the presence of cholesterol). This phase is characterised by an isotropic 31P NMR signal and is visualised by freeze-fracturing as particles and pits on the fracture faces of the lipid bilayer. As the most favourable model for this phase we propose the inverted micelle sandwiched in between the two monolayers of the lipid bilayer.

Calcium↗
PubMed1979

The interaction of spectrin-actin and synthetic phospholipids. II. The interaction with phosphatidylserine.

Sonicated vesicles of phosphatidylserine and phosphatidylserine/phosphatidylcholine mixtures were recombined with spectrin-actin from human erythrocyte ghosts. Morphological properties and physicochemical characteristics of the recombinates were studied with freeze etch electron microscopy, 31P NMR and differential scanning calorimetry. Sonicated dimyristoyl phosphatidylserine vesicles show a decrease in enthalpy change of the lipid phase transition upon addition of spectrin-actin. These vesicles collapse and fuse, into multilamellar structures in the presence of spectrin-actin, as demonstrated by freeze fracturing and NMR. Spectrin-actin cannot prevent the salt formation between phosphatidylserine and Ca2+, all phosphatidylserine is withdrawn from the lipid phase transition. In contrast a protection against the action of Mg2+ could be observed. Mixed bilayers of dimyristoyl phosphatidylserine/dimyristoyl phosphatidylcholine show phase separations at molar ratios above 1/1 (van Dijck, P.W.M., de Kruijff, B., Verkleij, A.J., van Deenen, L.L.M. and de Gier, J. (1978) Biochim. Biophys. Acta 512, 84--96). These phase spearations can be prevented by spectrin-actin. Ca2+-induced lateral phase separations in cocrystallizing phosphatidylserine/phosphatidylcholine mixtures, can be reduced by spectrin-actin. Formation of the Ca2+-phosphatidylserine salt, occurring in addition to lateral phase separation when mixtures contain more than 30 mol % phosphatidylserine, cannot be prevented by spectrin-actin.

Actins↗
PubMed1978

Comparative studies on the effects of pH and Ca2+ on bilayers of various negatively charged phospholipids and their mixtures with phosphatidylcholine.

(1) The thermotropic behaviour of dimyristoyl phosphatidylglycerol, phosphatidylserine, phosphatidic acid and phosphatidylcholine was investigated by differential scanning calorimetry and freeze-fracture electron microscopy as a function of pH and of Ca2+ concentration. (2) From the thermotropic behaviour as a function of pH, profiles could be constructed from which apparent pK values of the charged groups of the lipids could be determined. (3) Excess Ca2+ induced a shift of the total phase transition in 14 : 0/14 : 0-glycerophosphocholine and 14 : 0/14 : 0-glycerophosphoglycerol mixtures. In 14 : 0/14 : 0-glycerophosphocholine bilayers containing 16 : 0/16 : 0-glycerophosphoglycerol lateral phase separation was induced by Ca2+. (4) Up to molar ratios of 1 : 2 of 14 : 0/14 : 0-glycerophosphoserine to 14 : 0/14: 0-glycerophosphocholine, excess Ca2+ induced lateral phase separation. Addition to mixtures of higher molar ratios caused segregation into different structures: the liposome organization and the stacked lamellae/cylindrical organization. (5) Addition of excess Ca2+ to mixtures of 14 : 0/14 : 0-glycerophosphocholine and 14 : 0/14 : 0-phosphatidic acid caused, independent of the molar ratio, separation into two structural different organizations. (6) The nature of Ca2+-induced changes in bilayers containing negatively charged phospholipids is strongly dependent on the character of the polar headgroup of the negatively charged phospholipid involved.

Calcium↗
PubMed1978

Non-electrolyte permeability as a tool for studying membrane fluidity.

1. The reflection coefficient for the permeation of thiourea through bilayers of phosphatidylcholine is a function of the fatty-acid composition of the lipid molecules. By means of these reflection coefficients an index for membrane fluidity has been given to each of those lipids, relative to that of egg phosphatidylcholine. 2. The maximum number of water molecules that can copermeate with each molecule of solute by means of solute-solvent interaction is a function of the packing of the lipid molecules in the bilayer. This parameter has been used in this paper for characterizing the fluidity of cholesterol-containing membranes and for membranes with their lipids in the gel state.

Chemical Phenomena↗
PubMed1978

Phosphatidylinositol as the endogenous activator of the (Na+ + K+)-ATPase in microsomes of rabbit kidney.

Incubation of rabbit kidney microsomes with pig pancreatic phospholipase A2 produced residual membrane preparations with very low (Na+ + K+)-ATPase activity. The activity could be restored by recombination with lipid vesicles of negatively-charged glycerophospholipids. Vesicles of pure phosphatidylcholine and phosphatidylethanolamine were virtually inactive in this respect, but could reactivate in the presence of cholate. Incubation of the microsomes with a combination of phospholipase C (Bacillus cereus) and spingomyelinase C (Staphylococcus aureus) resulted in 90--95% release of the phospholipids. The residual membrane contained only phosphatidylinositol and still showed 50--100% of the (Na+ + K+)-ATPase activity.

Adenosine Triphosphatases↗
PubMed1978

Phase transitions in phospholipid model membranes of different curvature.

1. Nuclear magnetic resonance, light scattering and freeze fracturing electron microscopic techniques were used to characterize the size of unilamellar phospholipid vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphocholine. 2. Differential scanning calorimetric and light scattering analyses showed that very small unilamellar vesicles obtained by the sonication method exhibit a downward shifted, largely broadened phase transition with a slightly decreased enthalpy change when compared with multilayered liposomes. 3. The phase transition of vesicles with variable diameter as obtained by injection methods resembled the pattern of multilayered liposomes the more the diameter was increased. 4. Repeated cycling through the lipid phase transition was shown to have a progressive effect on a fusion process. This effect was strongly increased when the osmolarity of the medium was enhanced (e.g. by the addition of cryoprotectors). Furthermore it was shown that ice-water of the systems caused abrupt fusion of the lipid structures. 5. Controversial results in the literature on the thermotropic behavior of vesicles could be explained in terms of these fusion processes.

Calorimetry, Differential Scanning↗
PubMed1977

The interaction of spectrin - actin and synthetic phospholipids.

Using differential scanning calorimetry and freeze fracture electron microscopy interactions were studied between lipids and a spectrin - actin complex isolated from human erythrocyte membranes. With dispersions of 1,2-dimyristoyl-sn-glycero-3-phosphocholine, 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol and mixtures of these two compounds, which for experimental reasons were chosen as the lipid counterpart, such an interaction could clearly be deduced from changes in the temperature and the enthalpy of the phase transition. Furthermore it was demonstrated that the interaction with this membrane protein protects the bilayer against the action of Ca2+ and Mg2+ and prevents fusion of lipid vesicles which easily occurs in some of the systems when divalent ions were added to the pure lipid vesicles.

Actins↗
PubMed1977

Miscibility properties of binary phosphatidylcholine mixtures. A calorimetric study.

From data obtained by differential scanning calorimetry phase diagrams were constructed, using a thermodynamically based fitting method. The following binary mixtures of phosphatidylcholines in water were studied: 14:0/14:0-glycerophosphocholine/16:0/16:0-glucerophosphocholine, 14:0/14:0-glycerophosphocholine/18:0/18:0-glycerophosphocholine, 12:0/12:0-glycerophosphocholine/16:0/16:0-glycerophosphocholine, 18:1t/18:1t-glycerophosphocholine/14:0/14:0-glycerophosphocholine and 18:1t/18:1t-glycerophosphocholine/16:0/16:0-glycerophosphocholine. A comparison is made of the present results with those obtained using probe techniques and the differences are discussed.

Calorimetry↗
PubMed1976

The fusion of abnormal plasma lipoprotein (LP-X) and the erythrocyte membrane in patients with cholestasis studied by electronmicroscopy.

Adhesion followed by fusion of LP-X vesicles with the erythrocyte membrane is an important contribution to the erythrocyte enlargement in patients with intra or extra hepatic cholestasis. Adhesion of LP-X vesicles is demonstrated by thin section and freeze-etch electronmicroscopy. Fusion of LP-X with the erythrocyte membrane is deduced from biochemical data and freeze-etch electronmicroscopy in that the uptake of cholesterol and lecithin coincides with the increase in smooth areas on the fracture faces of the erythrocyte membrane.

Binding Sites↗
PubMed1975

The effect of chain length and lipid phase transitions on the selective permeability properties of liposomes.

This paper describes experiments showing the importance of the fatty acid chain length on the barrier properties of liposomal bilayers, prepared from saturated lecithins, under conditions of lateral phase separation. 1. Above the gel to liquid crystalline phase transition temperature, liposomes prepared from saturated lecithins with 14 or more carbon atoms per acyl chain exist as stable bilayers, which are practically impermeable to ions. 2. At temperatures well above the transition temperature dilauroyl phosphatidylcholine liposomes exhibited osmotic shrinkage, which was dependent on the ionic size of the solute used to bring about the osmotic gradient, indicating that the permeation through these less stable bilayers takes place mainly via individual diffusion of the permeating ions. 3. An enhanced release of trapped potassium from liposomes was demonstrated in the vicinity of the transition temperature. The extent of the increase, however, depended strongly on the length of the paraffin chain. 4. From measurements of the shrinkage behaviour of liposomes in the vicinity of the transition temperature it is concluded that the increased permeability decreases with increasing diameter of the permeating ion. This finding implies that the increased permeability at the transition temperature cannot be ascribed to "macroscopic" rupture of the liposomal membrane. The maximum permeability in the vicinity of the Tc is discussed in terms of probability and size distribution of statistical pore formation at the boundaries of liquid and solid domains.

Cations, Monovalent↗
PubMed1975

The role of phospholipid acyl chains in the activation of mitochondrial ATPase complex.

1. The role of length and unsaturation of phospholipid acyl chains in the activation of ATPase complex was studied with synthetic phosphatidylcholines and a phospholipid-dependent preparation obtained after cholate-extraction of submitochondrial particles (Kagawa, Y. and Racker, E. (1966) J. Biol. Chem. 241, 2467--2474). 2. Micelle-forming, short-chain phosphatidylcholines produced activation only at critical micellar concentration. The reactivated complex was cold-stable but the oligomycin sensitivity was low. 3. Bilayer-forming saturated phosphatidylcholines produced activation which was maximal at 9 carbon atoms in each chain but decreased sharply as the chain-length was increased and essentially disappeared at 14 carbon atoms. By contrast the oligomycin-sensitivity increased with the increase in chain length. 4. Activation of ATPase complex reappeared when bilayers were formed with long-chain unsaturated phosphatidylcholines. The activity was oligomycin sensitive. Significant inhibition of activity was observed also after incorporation of cholesterol into the bilayers. 5. By contrast the activation induced by negatively charged liposomes of diacylphosphatidylglycerol was independent on acyl-chain composition and occurred at very low amounts of phospholipid. 6. The discontinuity in the Arrhenius plot of activity of the ATPase complex reactivated with saturated phospholipids was found at temperatures close to the gel-to-liquid crystalline transition of the lipid showing that the activity of ATPase complex was sensitive to the physical state of membrane phospholipids. 7. It is concluded that (a) reactivation of ATPase complex by isoelectric phospholipids is an interfacial activation, the minimum requirement for the lipid effect being micelle formation. (b) In order to gain the properties of the native complex a stable lamellar phase is needed. Both activity and oligomycin sensitivity are regulated by the chain length and degree of unsaturation of phospholipid acyl chains.

Adenosine Triphosphatases↗