Biomedical subjects

G Arvidson

Publications and source records attributed to G Arvidson.

At least 19 recordsLinked to original sources

PubMed1997

Influence of membrane-spanning alpha-helical peptides on the phase behavior of the dioleoylphosphatidylcholine/water system.

The effect of solubilized hydrophobic peptides on the phase behavior of dioleoylphosphatidylcholine (DOPC)/water system was studied by 2H- and 31P-NMR spectroscopy and by x-ray diffraction, and partial phase diagrams were constructed. The utilized peptides were HCO-AWW(LA)5WWA-NHCH2CH2OH (WALP16), which is an artificial peptide designed to resemble a transmembrane part of a membrane protein; and VEYAGIALFFVAAVLTLWSMLQYLSAAR (Pgs peptide E), a peptide that is identical to one of the putative transmembrane segments of the membrane-associated protein phosphatidylglycerophosphate synthase (Pgs) in Escherichia coli. Circular dichroism spectroscopy suggests that both peptides are mostly alpha-helical in DOPC vesicles. The most striking features in the phase diagram of the WALP16/DOPC/water system are 1) a single lamellar liquid crystalline (L alpha) phase forms only at very low peptide concentrations. 2) At low water content and above a peptide/lipid molar ratio of approximately 1:75 a reversed hexagonal liquid crystalline (H[II]) phase coexists with an L alpha phase, while in excess water this phase forms at a peptide/lipid molar ratio of approximately 1:25. 3) At peptide/lipid ratios > or =1:6 a single H(II) phase is stable. Also, the Pgs peptide E strongly affects the phase behavior, and a single L alpha phase is only found at low peptide concentrations (peptide/lipid molar ratios <1:50), and water concentrations <45% (w/w). Higher peptide content results in coexistence of L alpha and isotropic phases. Generally, the fraction of the isotropic phase increases with increasing temperature and water concentration, and at 80% (w/w) water content only a single isotropic phase is stable at 55 degrees C. Thus, both peptides were found to be able to induce nonlamellar phases, although different in structure, in the DOPC/water system. The phase transitions, the extensions of the one-phase regions, and the phase structures observed for the two systems are discussed in terms of the molecular structure of the two peptides and the matching between the hydrophobic lengths of the peptides and the bilayer thickness of DOPC.

Amino Acid Sequence↗

PubMed1996

Two-dimensional 1H-NMR of transmembrane peptides from Escherichia coli phosphatidylglycerophosphate synthase in micelles.

Two 28-residue peptides, PTLLTLFRVILIPFFVLVFYKKKGKKKG [Pgs-(6-25)-peptidyl-KKKGKKKG; Pgs peptide A] and VEYAGIALFFVAAVLTLWSMLQYLSAAR [Pgs-(149-176)-peptide, Pgs peptide E], were synthesized and studied by CD and two-dimensional 1H-NMR spectroscopy. The first 20 amino acid residues of Pgs peptide A are identical to one predicted transmembrane segment (Pro6-Tyr25) of the integral membrane protein phosphatidylglycerophosphate synthase (Pgs) of Escherichia coli. Pgs peptide E is identical to another predicted transmembrane segment (Val149-Arg176), which is located in the C-terminal end of this lipid synthase. Pgs peptides A and E were dissolved in methanol or trifluoroethanol or were incorporated into solvent-free micelles of fully deuterated SDS. In all these systems, CD spectra of both peptides indicated an alpha-helical secondary structure. However, peptides that were solubilized in micelles exhibited the highest content of alpha-helix as judged from comparison of the CD spectra. Thermodynamically stable isotropic solutions at high peptide concentrations (1-3 mM) could only be obtained with the peptide incorporated in micelles; in organic solvents, significant peptide aggregation occurred. Relatively sharp peaks were obtained with 1H-NMR spectroscopy of the peptides in SDS micelles, which indicates rapid tumbling of the peptides in the micellar environment. Translational-diffusion coefficients of the micelles with and without peptide, determined by pulsed-field-gradient NMR, showed that the micellar size was unaffected by the solubilized peptide. The radius of the hydrated micelles was estimated to be about 2.7 nm (i.e. the mass of the aggregate is almost 30 kDa). Two-dimensional NMR spectroscopy of both peptides solubilized in the micelles indicated an alpha-helical conformation. This observation is strengthened by an investigation of the hydrogen exchange of the peptide amide protons, where significantly less exchange of the amide protons was observed in the middle of the peptides compared with the ends.

Amino Acid Sequence↗

PubMed1995

Structures of glucolipids from the membrane of Acholeplasma laidlawii strain A-EF22. III. Monoglucosyldiacylglycerol, diglucosyldiacylglycerol, and monoacyldiglucosyldiacylglycerol.

The structures of three glucolipids from the membrane of Acholeplasma laidlawii, strain A-EF22, were determined by high resolution 1H-NMR and 13C-NMR spectroscopy. The two most abundant glucolipids in this organism were shown to be 1,2-diacyl-3-O-(alpha-D-glucopyranosyl)-sn-glycerol (MGlcDAG) and 1,2-diacyl-3-O-[alpha-D-glucopyranosyl-(1 --> 2)-O-alpha-D- glucopyranosyl]-sn-glycerol (DGlcDAG). These structures agree with those determined previously by chemical analyses of the two most abundant glucolipids synthesized by the B strain of A. laidlawii. The structure of a newly discovered glucolipid in A. laidlawii strain A-EF22 was also determined. This lipid is an acylated derivative of DGlcDAG with the structure 1,2-diacyl-3-O-[alpha-D-glucopyranosyl-(1 --> 2)-O-(6-O-acyl-alpha-D- glucopyranosyl)]-sn-glycerol. The existence of this lipid was detected by 1H-NMR spectroscopy in preparations of MGlcDAG which had been judged by thin-layer chromatography to be pure. The biosynthesis of the glucolipids and their role in the metabolic lipid regulation are briefly discussed.

Acholeplasma laidlawii↗

PubMed1995

Complexes between cationic liposomes and DNA visualized by cryo-TEM.

The association structures formed by cationic liposomes and DNA-plasmids have been successfully employed as gene carriers in transfection assays. In the present study such complexes was studied by cryo-TEM (cryo-transmission electron microscopy). Cationic liposomes made up by DOPE (dioleoylphosphatidylethanolamine) and various amounts of three different cationic surfactants were investigated. The cryo-TEM analysis suggests that an excess of lipid in terms of charge, leads to entrapment of the DNA molecules between the lamellas in clusters of aggregated multilamellar structures. With increasing amounts of DNA free or loosely bound plasmids were found in the vicinity of the complexes. The importance of the choice of surfactant, as reported from many transfection assays, was not reflected in changes of the type of DNA-vesicle association. A tendency towards polymorphism of the lipid mixtures is reported and its possible implications are discussed.

Cations↗

PubMed1995

Phase equilibria and molecular packing in the N,N-dimethyldodecylamine oxide/gramicidin D/water system studied by 2H nuclear magnetic resonance spectroscopy.

A partial phase diagram of the system N,N-dimethyldodecylamine oxide (DDAO)/water/gramicidin D was determined by 2H-NMR. Both 2H2O and perdeuterated DDAO (DDAO-d31) were studied by solid state NMR techniques. Addition of gramicidin D to the micellar (L1), normal hexagonal (HI) and cubic (I) phases of DDAO induces phase separations, giving two-phase regions, which all contain a lamellar (L alpha) phase. The L alpha phase containing gramicidin is characterized by larger order parameters for DDAO-d31 compared with the corresponding order parameters in the L alpha and HI phases of DDAO-d31/H2O. The L alpha phase may stay in equilibrium with any other phase in the phase diagram. The DDAO exchange between the coexisting phases is slow on the NMR timescale, which is why the recorded NMR spectrum consists of superimposed spectra from the different phases occurring in the sample. Gramicidin D can be solubilized in appreciable quantities only in the lamellar phase of DDAO-d31. Increasing amounts of gramicidin in the liquid crystalline phases result in a continuous increase in the molecular ordering up to about 5 mol% gramicidin, where a plateau is reached. This is consistent with a recent theoretical model describing the influence on the ordering of lipids by a membrane protein with larger hydrophobic thickness than the lipid bilayer. The solvent used for dissolving gramicidin at the incorporation of the peptide in the lipid aggregates has no effect on the 2H-NMR lineshapes of DDAO-d31. It is concluded that gramicidin is solubilized in the L alpha phase and that it always adopts the channel conformation independent of a particular solvent. The channel conformation is also supported by CD studies. In some of the samples, macroscopic orientation of the lipid aggregates is observed. It is concluded that DDAO-d31 in the binary system favors an orientation with the long axis of the hydrocarbon chain perpendicular to the magnetic field, whereas when gramicidin D is present the hydrocarbon chain orients parallel to the magnetic field. This is explained by the fact that gramicidin aligns with its helical axis parallel to the magnetic field, thereby forcing also the DDAO-d31 molecules to obtain such an orientation.

Chemical Phenomena↗

PubMed1992

Decreased erythrocyte cholesterol/phospholipid ratio in untreated patients with essential hypertension.

The erythrocyte cholesterol/phospholipid ratio was determined in eight patients with untreated essential hypertension and compared with that of eight age-matched control subjects. The ratio was significantly lower in patients (Wilcoxon's paired rank test; P less than 0.01), and a correlation existed between the ratio and serum cholesterol concentration in patients (r = 0.63) but not in controls (r = 0.02). A reduction in the cholesterol/phospholipid ratio may play a direct role in destabilizing the plasma membrane, which will in turn result in an increase in membrane permeability in essential hypertension.

Adult↗

PubMed1990

Occurrence of phospholipase A2 and lysophospholipase in a gastric H,K-ATPase-containing membrane fraction, and the formation of lysophosphatidylcholine in stimulated pig parietal cells.

A membrane fraction containing H,K-ATPase (EC 3.6.1.36) was prepared from pig gastric mucosa and found to contain phospholipase A2 (EC 3.1.1.4) and lysophospholipase (EC 3.1.1.5) activities. Washing the membranes decreased their protein content by 25%. Recovery profiles of H,K-ATPase, phospholipase A2 and lysophospholipase were similar for membranes washed either with water or with 0.15 or 1.5 M KCl. Nearly identical distribution profiles were obtained for the three enzyme activities after centrifugation of washed vesicle membranes on a linear sucrose gradient. The phospholipase A2 activity was stimulated by calcium and increased further in the presence of calmodulin. The amount of cellular radioactively labelled lysophosphatidylcholine was doubled upon cholinergic stimulation of isolated parietal cells prelabelled with [3H]glycerol or 32Pi. The liberated lyso[32P]phosphatidylcholine had its acyl chain in the sn-1 position, which implies an activation of a phospholipase A2. These findings indicate that secretagogues which increase the cytosolic Ca2+ concentration, i.e. acetylcholine, histamine and gastrin, may activate a phospholipase A2 in the parietal cell.

Adenosine Triphosphatases↗

PubMed1990

Calcium and calmodulin stimulate phospholipase A2 and fusion of H,K-ATPase-containing membrane vesicles isolated from pig gastric mucosa.

Fusion of pig gastric H,K-ATPase- and phospholipase A2-containing vesicles in vitro was studied by electron microscopy and by monitoring the change in fluorescence of octadecyl rhodamine B-labelled vesicles. Ca2+ stimulated fusion of the vesicles, and the fusion rate showed a positive correlation with the activity of the phospholipase A2. Both the Ca2(+)-stimulated fusion rate and the Ca2(+)-dependent phospholipase A2 activity were further enhanced by the presence of calmodulin. The present results supported our previous findings (Olaisson et al. 1990) and further indicate that the phospholipase A2 associated with the H,K-ATPase-containing membranes might play a central role in membrane fusion processes in the stimulated parietal cell.

Adenosine Triphosphatases↗

PubMed1989

Human prostasome membranes exhibit very high cholesterol/phospholipid ratios yielding high molecular ordering.

Lipid analysis and ESR studies were carried out on prostasomes isolated from human semen. Cholesterol plus phospholipids amounted to approximately 0.80 mumol per mg protein with a striking quantitative domination of cholesterol over the phospholipids, the molar ratios of cholesterol/sphingomyelin/glycerophospholipids being 4:1:1. Saturated and monounsaturated fatty acids were dominating both in the glycerophospholipids and in sphingomyelin. The order parameters, S, deduced from ESR spectra of spin-labelled fatty acids incorporated into prostasome membranes order parameters, S, deduced from ESR spectra of spin-labelled fatty acids incorporated into prostasome membranes were very high, viz. 0.75 for 5-doxylstearic acid and 0.30 for 16-doxylstearic acid at 25 degrees C. Slightly lower values were obtained for the spin-labelled fatty acids when they were incorporated into dispersions of extracted prostasome lipids or into synthetic lipid mixtures of similar composition. The highly ordered lipids in the prostasome membrane thus seemed to be minimally perturbed by proteins in the membrane and ESR spectra showed no signs of immobilized lipids.

Adenosine Triphosphatases↗

PubMed1988

Possible regulation of cation-induced pinocytosis in Amoeba proteus by phospholipase A.

We have studied the effects of exogenous phospholipids and compounds which are known to alter the activity of phospholipase A (PLA) on Ca2+-dependent, Na+-induced pinocytosis in Amoeba proteus. The PLA-inhibitors mepacrine, p-bromophenacyl bromide (pBPB) and Rosenthal's inhibitor depressed pinocytosis. Normal pinocytotic intensity was restored by the addition of Ca2+ or picomolar concentrations of lysolecithin. Very low concentrations of lysophospholipids and different molecular species of lecithins increased the capacity for pinocytosis in starved amoebae. The effect of the lecithins but not of the corresponding lysolecithins was abolished by PLA-inhibitors. Also, the restoration of the pinocytotic capacity of starved amoebae by melittin and mastoparan, which are known to stimulate PLA, was inhibited by mepacrine and pBPB. Isolated amoeba plasma membranes contain phospholipase A1 and A2 activity and the amoebae secrete a lipid (PRF, pinocytosis regulating factor) which has lysolecithin-like effects on pinocytosis. The enzyme activities and the release of PRF were markedly decreased by the PLA-inhibitors. Our observations support the hypothesis that PRF is a lysophospholipid that may constitute a signal for the formation of pinocytotic channels in the initial stages of pinocytosis. The phospholipase A activity of the amoeba must therefore be assigned an important role in the regulation of the Ca2+-dependent, cation-induced pinocytosis.

Amoeba↗

PubMed1987

Phase equilibria of the ternary system 1-palmitoyl-sn-glycero-3-phosphocholine/oleic acid/water studied by NMR.

Part of a phase diagram for the system 1-palmitoyl-sn-glycero-3-phosphocholine (PamGroPCho)/oleic acid/water has been constructed from mainly 31P-NMR data and a previous determination of the phase equilibria of the binary PamGroPCHo/water system. It was found that the appearance of the phase diagram is very similar to those found for several simple soap/fatty acid/water or soap/long-chain alcohol/water systems. The most striking features observed are: (1) the lamellar phase can swell towards very high water contents (2) vesicles are formed after sonication and (3) the cubic liquid crystalline phase disappears upon addition of very small amounts of oleic acid. The self-association of the amphiphiles and the shape of the aggregates are discussed in terms of existing first-order approximative theories.

Lysophosphatidylcholines↗

PubMed1987

Hydrophobic molecules in lecithin-water systems. I. Formation of reversed hexagonal phases at high and low water contents.

The system dioleoylphosphatidylcholine (DOPC)-n-dodecane-2H2O was investigated with different nuclear magnetic resonance (NMR) techniques: (a) a tentative phase diagram was determined by 2H- and 31P-NMR, (b) translational diffusion coefficients were determined for the three components with the pulsed magnetic field gradient NMR technique, and (c) order parameters for perdeuterated n-dodecane were obtained by 2H-NMR. n-Dodecane induces the formation of reversed hexagonal (HII) phases at low and high water concentrations, and cubic phases at low water contents. The translational diffusion coefficients of n-dodecane in a cubic phase with 6 mol water per mol DOPC, and in an HII phase with 48 mol water per mol DOPC, were just approximately 2.5 times lower than in pure dodecane. Perdeuterated dodecane gave large quadrupole splittings in a lamellar phase, much smaller in an HII phase at low water contents, and a narrow single peak in an HII phase at high water contents. This latter observation indicates that a large fraction of the dodecane molecules is located in separate regions between the water cylinders. Our results support the model given by Gruner concerning the aggregation of membrane lipids in the presence of hydrophobic molecules.

Deuterium↗

PubMed1986

Relationship between three-dimensional arrays of "lipidic particles" and bicontinuous cubic lipid phases.

Several lipid-water mixtures form phases that give rise to freeze-fracture replicas exhibiting three-dimensional regular arrays of closely packed globular elements, often called "lipidic particles". These phases have often been poorly classified with respect to long-range organization and symmetry and have in most cases been asserted to be built up by closed lipid aggregates, such as reversed micelles. However, studies of phases giving rise to the above-mentioned freeze-fracture replicas, with X-ray diffraction and the nuclear magnetic resonance pulsed field gradient diffusion technique, have revealed that they are cubic liquid-crystalline phases and with one exception bicontinuous phases, i.e., cubic phases in which both the hydrocarbon and the water regions are continuous. Up to now the only known exception is a cubic phase composed of closed rod-shaped micelles of the normal type. Thus it is not possible to decide from a freeze-fracture image of a cubic phase, showing three-dimensional arrays of "lipidic particles", if the phase is bicontinuous or composed of closed lipid aggregates. Hitherto, it has not been shown that a biological membrane lipid-water system is able to form a cubic liquid-crystalline phase consisting of reversed micelles. The existence of such a phase is also improbable considering the location in the phase diagrams of cubic phases formed by biological membrane lipid-water systems.

Diglycerides↗

PubMed1985

Phase equilibria in four lysophosphatidylcholine/water systems. Exceptional behaviour of 1-palmitoyl-glycerophosphocholine.

The phase equilibria in four lysophosphatidylcholine/water systems were investigated at different temperatures. Each of the 1-palmitoyl-, 1-stearoyl-, 1-oleoyl- and 1-linoleoyl-sn-glycero-3-phosphocholines was dispersed in heavy water at different concentrations. The phase structures were determined by 2H-, 14N- and 31P-NMR, polarization microscopy and low-angle X-ray diffraction. The phase diagrams of the oleoyl and linoleoyl systems were quite similar. At room temperature and with decreasing water content the isotropic micellar solution was followed by a hexagonal phase and then a cubic phase. Finally the lamellar phase appeared before the region of hydrated crystals. The same sequence of phases was observed in the stearoyl system at elevated temperatures. The palmitoyl system differed from the others: here a cubic phase followed after the micellar solution, then came a hexagonal phase and after this a lamellar phase. In general the lysophosphatidylcholines seem to behave similarly to the many soaps and detergents as they show the same sequence of isotropic micellar solution, hexagonal phase, lamellar phase with interspersed cubic phases. The presently established phase diagrams demonstrate that the major lysophosphatidylcholines which may be generated by phospholipase A2 in mammalian cell membranes, viz. 1-palmitoyl- and 1-stearoyl-glycerophosphocholines differ greatly in their packing properties. The extraordinary ability of 1-palmitoyl-glycerophosphocholine to form a cubic phase in equilibrium with a micellar solution is of particular interest with regard to the possible occurrence of cubic structures in biomembranes during the process of fusion.

Lysophosphatidylcholines↗

PubMed1985

Phospholipid organization in H,K-ATPase-containing membranes from pig gastric mucosa.

The transverse distribution of the phospholipids in vesicular H+-translocating membranes prepared from pig gastric mucosa was investigated with the aid of phospholipase C, sphingomyelinase, and trinitrobenzenesulfonic acid. The major part (80-90%) of the phosphatidylcholine and the phosphatidylethanolamine, 60% of the phosphatidylserine, and 45% of the sphingomyelin was located on the external, cytoplasmic side of the vesicle membranes. After treatment with phospholipase C the vesicles still behaved as osmometers and appeared as closed vesicles on the electron micrographs. 31P NMR indicated that the phospholipids in untreated vesicles as well as the unhydrolyzed phospholipids in phospholipase C-treated vesicles were arranged in lamellar structures. The 31P NMR spectrum of untreated vesicles to which Pr3+ ions had been added supported the conclusion that the major part of the membrane phospholipids was located on the external surface of the vesicles. A small fraction of the lipids, 3.6 mol %, was found to consist of glycosphingolipids which occurred at a concentration of 52 nmol/mg of protein.

Adenosine Triphosphatases↗

PubMed1984

Characterization of proton-transporting membranes from resting pig gastric mucosa.

Membrane vesicles were purified from resting corpus mucosa of pig stomachs by velocity-sedimentation on a sucrose-Ficoll step gradient. Two vesicular fractions containing the (H+ + K+)-ATPase were obtained. One fraction was tight towards KCl, the other was leaky. At 21 degrees C maximal (H+ + K+)-ATPase activities of 0.8 and 0.4 mumol X mg-1 X min-1, respectively, were observed in lyophilized vesicles. The vesicles contained a membrane-associated carbonic anhydrase, the activity of which was in 100-fold excess of the maximal ATPase activity. Both vesicular fractions were rich in phosphatidylcholine, phosphatidylethanolamine, sphingomyelin and cholesterol. The characteristics of ion permeability and transport in the tight vesicles were in agreement with corresponding data for vesicles of a tubulovesicular origin in the parietal cell. Measurement of the rate of K+ uptake into the vesicles was based on the ability of K+ to promote H+ transport. The uptake was slow and dependent on the type of anion present. The effectiveness in promoting uptake of K+ by anions was SCN- greater than NO3- greater than Cl- much greater than HCO3- greater than SO4(2-). Uptake of K+ was much more rapid at alkaline pH than at neutral or at acidic pH. Addition of CO2 at alkaline pH strongly stimulated the rate of H+ accumulation in the vesicles. The initial part of this stimulation was sensitive to acetazolamide, an inhibitor of carbonic anhydrase. A model how the (H+ + K+)-ATPase and the carbonic anhydrase may co-operate is presented. It is concluded that membrane vesicles of a tubulovesicular origin can produce acid.

Adenosine Triphosphatases↗

PubMed1984

Effect of hypoglycemic sulfonylureas on Ca2+ fluxes across lipid bilayers.

Black lipid membranes and liposomes loaded with Ca2+ or 5,6-carboxyfluorescein were used for exploring the mechanism of action of insulin-releasing sulfonylureas. Unlike the Ca2+/H+ exchanging ionophore A-23187, tolbutamide did not stimulate the net efflux of Ca2+ from the liposomes. Glibenclamide caused a sustained release of Ca2+, but this effect could be attributed to labilization of the liposomal membrane as indicated by a quantitatively similar loss of the stability marker 5,6-carboxyfluorescein. Unlike the neutral ionophore nonactin or the channel forming quasi-ionophore gramicidin A, the sulfonylureas did not alter the conductance of black lipid membranes in medium containing Na+, K+, Ca2+, Mg2+, and Cl-. It is concluded that the sulfonylureas tested lack ionophore properties but that glibenclamide can labilize membranes.

Biological Transport↗

PubMed1983

The interactions between monovalent ions and phosphatidyl cholines in aqueous bilayers.

The interactions of lithium and sodium ions and water with phosphatidylcholine bilayers have been studied by means of 7Li, 23Na and 2H NMR quadrupole splittings. The experimental results are interpreted in terms of a simple three-site model with two anisotropic sites ('binding' sites) and one isotropic site ('free' ions and water molecules). The findings obtained for the zwitterionic model membrane are compared with previous investigations of lamellar phases composed of ionic and nonionic amphiphiles. It is shown that the data obtained are compatible with our previous suggestion [Lindblom, G., Persson, N.-O., and Arvidson G. (1976) Adv. Chem. Ser. 152, 121] that an increase in the salt content in the water layer induces a conformational change in the polar head group of phosphatidylcholine. Thus at high salt concentration the phosphocholine head group tends to be oriented perpendicular to the lipid bilayer surface. The study also shows that increasing the amount of salt leads to a squeezing out of water between the bilayers. This is interpreted in terms of a reduction of the repulsion forces between the bilayers.

Lipid Bilayers↗