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P Laggner

Publications and source records attributed to P Laggner.

At least 55 records · Page 3Linked to original sources
PubMed1987

Structure and thermodynamics of the dihexadecylphosphatidylcholine-water system.

X-ray small- and wide-angle diffraction, differential scanning calorimetry (DSC), temperature scanning densitometry (TSD) and electron microscopy were used to study the lyotropic and thermotropic properties of the system 1,2-O-dihexadecyl-sn-glycero-3-phosphocholine-water over a wide range of compositions from the dry lipids to a large excess of water, and in the temperature range between 0 degrees C and 150 degrees C. The results were used to construct a temperature-composition phase diagram. The phases have been characterized with respect to their molecular arrangements and hydrocarbon chain packing subcells. In the fully hydrated state (greater than 45 wt% H2O) four thermotropic phases were found, with readily reversible transitions at 5 degrees C, 32.5 degrees C and 43.6 degrees C, respectively. The two lower temperature phases deviate from all others in consisting of bilayers with fully interdigitated hydrocarbon chains, while above 32.5 degrees C the structures resemble closely those of the analog diester lipid, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). At hydrations between 30 and 45 wt% H2O, and below 32 degrees C, interdigitated and non-interdigitated multilayers coexist in one coherent phase. A bilayer tilting mechanism is proposed for the formation of this coexistence of two regular structures. Below 30 wt% H2O, hydrated 1,2-O-dihexadecyl-sn-glycero-3-phosphocholine (DHPC) exists in lamellar, non-interdigitated bilayers, showing very weak interbilayer swelling. There, the water molecules appear to occupy voids between the polar headgroups.

Calorimetry, Differential Scanning↗
PubMed1987

Thermal phase behaviour and structure of hydrated mixtures between dipalmitoyl- and dihexadecylphosphatidylcholine.

Mixtures of 1,2-dipalmitoyl- and 1,2-O-dihexadecyl-sn-glycero-3-phosphocholine (DPPC and DHPC) in dispersion with excess water were studied by differential scanning calorimetry (DSC) and X-ray diffraction techniques. The transition parameters of the main gel-to-liquid crystalline transition show a monotonous dependence on the composition, indicating ideal miscibility of the two lipids, in keeping with the closely similar structures of the pure, hydrated lipids in the P beta' and L alpha states. The pre-transition shows a depression to a minimum temperature of 23 degrees C occurring around equimolar mixtures. Below the pre-transition temperatures, the L beta' gel phase of DPPC maintains bimolecular structure up to DHPC admixtures of 50 mol%, with adaptations in hydrocarbon chain packing and multilayer periodicity. On the side of DHPC, the interdigitated gel structure shows full solubility for DPPC up to equimolarity without major structural changes. The crystalline Lc-phase of DPPC exhibits immiscibility with DHPC, demonstrated by the fact that the subtransition is abolished already at less than 15 mol% DHPC. DHPC, below its subtransition, can accommodate up to 50 mol% DPPC within an interdigitated layer structure with unperturbed, crystalline hydrocarbon chain packing.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1984

Thermotropic properties and molecular dynamics of cholesteryl ester rich very low density lipoproteins: effect of hydrophobic core on polar surface.

Cholesteryl ester rich very low density lipoproteins (CER-VLDL), isolated from the plasma of rabbits fed a hypercholesterolemic diet, have been studied by differential scanning calorimetry (DSC), 13C nuclear magnetic resonance (NMR), and spin-label electron paramagnetic resonance (EPR) to determine the temperature-dependent dynamics of cholesteryl esters in the hydrophobic core and of phospholipids on the polar surface. Intact CER-VLDL exhibit two DSC heating endotherms; these occur at 40-42 and 45-48 degrees C. Cholesteryl esters isolated from CER-VLDL also exhibit two DSC endotherms; these occur at 50.0 and 55.1 degrees C and correspond to the smectic----cholesteric and cholesteric----isotropic liquid-crystalline phase transitions. A model mixture containing cholesteryl linoleate, oleate, and palmitate in a ratio (0.21, 0.51, and 0.28 mol fraction) similar to that in CER-VLDL exhibited comparable DSC endotherms at 45.2 and 51.5 degrees C. CER-VLDL at 37 degrees C gave 13C NMR spectra that contained no resonances assignable to cholesteryl ring carbons but detectable broad resonances for some fatty acyl chain carbons, suggesting the cholesteryl esters were in a liquid-crystalline state. When the mixture was heated to 42 degrees C, broad ring carbon resonances became detectable; at 48 degrees C, they became narrow, indicating the cholesteryl esters were in an isotropic, liquid-like state. With increasing temperature over the range 38-60 degrees C, the resonances for cholesteryl ring carbons C3 and C6 in CER-VLDL narrowed differentially. Similar spectral changes were observed for the synthetic cholesteryl ester mixture, except they occurred at temperatures about 10 degrees C higher. These results indicate that the two DSC transitions in CER-VLDL do not directly correlate with the smectic----cholesteric and cholesteric----isotropic transitions exhibited by pure cholesteryl esters. (5-Doxylpalmitoyl)-phosphatidylcholine (5-DP-PC) and (12-doxylstearoyl)phosphatidylcholine (12-DS-PC) were used to probe the polar surface monolayer of CER-VLDL; the corresponding cholesteryl esters (5-DP-CE and 12-DS-CE) were used to probe the hydrophobic core. None of these probes in CER-VLDL detected an abrupt change in EPR order parameters, S, or maximum splitting, 2T max, over the temperature range 20-58 degrees C even though 12-DS-PC and 5-DP-PC can detect phase transitions in phospholipid bilayers and 12-DS-CE and 5-DP-CE can detect phase transitions in neat cholesteryl esters. However, 12-DS-CE and 5-DP-CE did detect a much greater acyl chain order for the neutral lipids of CER-VLDL than for those of normal triglyceride-rich VLDL.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

In vitro modification of the chemical composition of human plasma low density lipoproteins: effects of morphology and thermal properties.

The effects of enzymatic action on human low density lipoproteins (LDL) occurring during in vitro incubation of plasma have been studied by chemical analysis, analytical ultracentrifugation, negative stain electron microscopy and X-ray small angle scattering. Chemically, the action of cholesteryl ester exchange and transfer proteins(s) (CEPT) leads to a relative increase in trigylcerides at the expense of cholesteryl esters. Morphologically, the particles maintain their characteristic features detectable by X-ray small angel scattering. Additional action of lecithin/cholesterol acyl transferase (LCAT) causes mainly a decrease in polar lipid contents and a reduction in particle size. The associated changes in the thermotropic transition were found to be strongly correlated to the triglyceride/cholesteryl ester ratio.

Carrier Proteins↗
PubMed1984

Structure of the cholesteryl ester core of human plasma low density lipoproteins: selective deuteration and neutron small-angle scattering.

The structural arrangement of cholesteryl esters in human plasma low density lipoproteins (LDL) has been studied by selective deuteration and neutron small-angle scattering. LDL were labeled by in vitro exchange with two different kinds of deuterated cholesteryl esters, one labeled in the fatty acyl chain (cholesteryl myristate-d27) and the other in the branched side chain of cholesterol (cholesteryl-25,26,27-d7 oleate). Neutron scattering data from deuterated and protonated LDL were compared to identify the locations of the fatty acyl and cholesterol side chain moieties. Below the thermotropic transition, radii of gyration of 60 A and 70 A were obtained for these two domains, respectively, indicating that the cholesteryl nuclei are situated more distantly from the center than the fatty acyl chains. At 37 degrees C, above the thermotropic transition of the cholesteryl esters in LDL, both parts have similar radii of gyration of approximately 56 A. This information is used in a discussion of possible structural models for the apolar lipid core of LDL.

Cholesterol Esters↗
PubMed1983

Cooperative effects in the interaction between melittin and phosphatidylcholine model membranes. Studies by temperature scanning densitometry.

The interaction between the peptide melittin from bee venom with multilamellar liposomes of dipalmitoylphosphatidylcholine or egg yolk phosphatidylcholine has been studied by the method of temperature scanning densitometry, yielding information on the specific volume of the association products and on the changes during the thermotropic transition of the lipids. The effects of the interaction were found to be biphasic with respect to melittin concentration; below 10(-3) mol per mol of phospholipid, an increase in transition temperature, abolition of the pretransition, a reduction in the transition volume of the lipids by about 25%, and a nonadditive increase in apparent specific volume of the complexes were observed. Only minor changes in these parameters could be detected between molar ratios of 10(-3) and 10(-2). Above 1 mol % melittin, the transition temperature decreased and the transition volume approached zero around 10 mol %. Since the effects in the low concentration range cannot be accounted for only by local perturbations around the actual sites of interaction, it is concluded that the interaction involves long range effects of melittin affecting several hundreds of phospholipid molecules. The results are discussed in terms of a phospholipid cluster model, whereby the interaction with melittin leads to a cooperative transition of entire clusters to a state of expanded volume. It is suggested that this transition may be important to the activating effect of melittin on membrane enzymes and to enhanced membrane permeability and lysis.

Bee Venoms↗
PubMed1982

Structural variability of tRNA: small-angle x-ray scattering of the yeast tRNAphe-Escherichia coli tRNAGlu2 complex.

The structure of the complex formed in solution between yeast tRNAPhe and Escherichia coli tRNAGlu2 has been studied by small-angle x-ray scattering. The complex has a radius of gyration of 4.0 nm and an electron-pair distance distribution that is incompatible with a model composed to two tRNAs joined at their complementary anticodons and exhibiting the L shape seen in the crystal. Instead a model in which the two tRNAs, still bound via the anticodons, assume a conformation with the acceptor arms folded toward the anticodon arms agrees with the observed scattering curves.

Anticodon↗
PubMed1981

Neutron small angle scattering on selectively deuterated human plasma low density lipoproteins. The location of polar phospholipid headgroups.

Human plasma low density lipoproteins (LDL) were deuterated in the phospholipid headgroup region by exchange with phosphatidylcholine-N(CD3)3-apolipoprotein A complexes. The exchange was associated with a net transfer of phosphatidylcholine to LDL leading to an increase in total phospholipid content by 27%. Practically all of the endogenous phosphatidylcholine including lysophosphatidylcholine, and about one-third of the sphingomyelin pool was found to be exchangeable. Immunochemically, deuterated LDL was identical with native LDL. The hydrodynamic and ultrastructural properties were closely similar for the two particle species apart from a slight increase in overall particle size by about 2%. Both native and deuterated LDL were investigated by neutron small angle scattering at several representative contrasts in H2O/D2O buffers. Subtraction of the scattering amplitudes of native from deuterated LDL resulted in a radius of gyration of 103 +/- 5 A for the N(CD3)3 groups, and in a structure factor resembling that of a thin, spherical shell. Evaluation of the contrast variation experiments in combination with previous data from x-ray small angle scattering (Laggner, P., and Mueller, K. (1978) Q. Rev. Biophys. 11, 371-425) indicates that the phospholipids form a spherical monolayer shell in the radial range between 75 A and 103 A around the core of cholesteryl esters and triglycerides. For the protein moiety, a radius of gyration of 110 A was calculated, indicating that it is located, on average, 5 to 10 A from the polar phospholipid headgroups toward the aqueous environment.

Cholesterol↗
PubMed1981

Structure of two subfractions of normal porcine (Sus domesticus) serum low-density lipoproteins. X-ray small-angle scattering studies.

Two subfractions of low-density lipoproteins (LDL) were isolated from normal pig (Sus domesticus) serum by a combined method including precipitation, ultracentrifugation, and gel chromatography. The fractions recovered from the buoyant density ranges 1.020-1.050 and 1.050-1.090 g/mL, denoted as LDL1 and LDL2, respectively, were studied with regard to structure and thermotropic behavior by X-ray small-angle scattering and were compared to human serum low-density lipoprotein of density 1.020-1.063 g/mL. The average molecular weights determined from the scattering intensities on absolute scale were 2.6 X 10(6) and 2.0 X 10(6) for LDL1 and LDL2, respectively. The maximum particle diameters were found to be 24 and 21 nm, respectively. Both species were found to have quasi-spherical symmetry and to display the thermotropic transition of the apolar lipids within the particle core similar to human LDL. The width of the transition was approximately 9 degrees C in both cases, but the midpoint transition temperature was higher by 8 degrees C for LDL1 (33 degrees C) than for LDL2 (25 degrees C). Despite their different sizes and thermotropic behavior, the two porcine LDL subfractions appear to be built according to the same structural principle as human LDL in the molecular organization of the apolar lipids within the particle core.

Animals↗
PubMed1979

Structure of the dimyristoylphosphatidylcholine vesicle and the complex formed by its interaction with apolipoprotein C-III: X-ray small-angle scattering studies.

Single bilayer vesicles of dimyristoylphosphatidylcholine have been investigated by small-angle X-ray scattering at 28 degrees C. The results indicate that these vesicles are hollow spherical shell structures with an outer radius of approximately 12 nm and a molecular weight of (3.2 +/- 0.5) X 10(6). The shell was found to be 4.4 +/- 0.2 nm thick with a cross-sectional electron-density profile characteristic for a single phospholipid bilayer. Upon interaction of these vesicles with apolipoprotein C-III from human very low density lipoproteins at a protein/lipid ratio greater than 0.08 (g/g), a complex containing 0.25 g of protein/g of lipid, with molecular weight of (3.9 +/- 0.4) X 10(5), is formed. The shape analysis indicates a highly asymmetric particle with an internal partition of low and high electron density resembling that produced by a bilayer structure. Model calculations and curve-fitting procedures show good agreement between the experimental scattering curve and that computed for an oblate ellipsoidal structure with dimensions of 17 X 17 X 5 nm and a 1 nm thick shell of high electron density surrounding the core of low electron density.

Apolipoproteins↗
PubMed1978

The structure of human-plasma low-density lipoprotein B. An X-ray small-angle scattering study.

1. X-ray small-angle scattering of human plasma lipoprotein B of the low-density fraction (rho = 1.016--1.060 g.cm-3) has been recorded to high precision at different electron density contrasts. 2. The overall structure of the particles is characterized by a quasi-spherical shape and radial symmetry. A maximum diameter of 23 nm and a molecular weight of 2.4 X 10(6) have been determined. 3. The internal structure is described in terms of a model consisting of spherical layers with different electron densities indicating that the neutral lipids are arranged in the core of the molecule up to a radius of about 8 nm surrounded by a monolayer of free cholesterol, phospholipids and protein. The neural lipids are shown to be in an ordered, liquid crystalline state at 4 degrees C and to undergo a thermotropic transition into a disordered state at higher temperatures.

Cholesterol↗
PubMed1977

The lipid bilayer structure of the abnormal human plasma lipoprotein X. An X-ray small-angle-scattering study.

The structure of the abnormal lipoprotein X occurring in the plasma of patients with obstructive jaundice was investigated by X-ray small-angle scattering. The data were analyzed by discussing the distance distribution functions obtained directly from the experimental data by Fourier transformation, involving no a priori assumptions. The results provide evidence for lipoprotein X being essentially a random distribution of lamellae with a thickness of 5.1 nm and are consistent with hollow spherical (vesicular) structures of outer diameters greater than 30 nm with some overall size heterogeneity. Under the experimental conditions chosen, lipoprotein concentrations between 0.01 and 0.18 g/ml in in buffers of low ionic strength, lateral stacking as observed in negative-stain electron microscopy does not occur. The electron density profile perpendicular to the lamellar plane indicates that a lipid bilayer is the underlying structural principle, with the protein moieties partly bound within the polar head-group regions and partly occluded in soluble form in the vesicle interior.

Cholestasis↗
PubMed1977

Separation of subclasses of human serum high density lipoproteins by zonal ultracentrifugation.

An improved one-step method for the preparative separation of three subfractions of high-density lipoproteins from normal human serum has been developed. It employs the method of rate zonal ultracentrifugation in a z-60 rotor using a discontinuous NaBr gradient in the density range of 1.0-1.4. The density gradients were monitored directly by a flow-through density meter allowing the direct read-out of the actual densities in the process of filling and emptying the rotor. The separation of the three density fractions from 5 to 15 ml serum was achieved during a single 12 hours run at 59.000 rpm. The three fractions showed characteristically different patterns on polyacrylamide gel electrophoresis and differences in their lipid and protein composition.

Centrifugation, Zonal↗