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J Seelig

Publications and source records attributed to J Seelig.

At least 91 records · Page 5Linked to original sources
PubMed1990

A homonuclear shift correlated and spatially localized spectroscopy using stimulated echoes.

A new method which combines localized high-resolution proton NMR spectroscopy with two-dimensional correlated spectroscopy using stimulated echoes is presented. Stimulated-echo correlated spectroscopy (STECSY) is a straightforward extension of the STEAM method. Experiments with phantoms illustrate the efficacy of STECSY. An in situ application on rat adipose tissue demonstrates that STECSY is a helpful tool with which to select and assign resonances in complex 1H NMR spectra.

Adipose Tissue↗
PubMed1990

Two-volume acquisition in image-guided proton spectroscopy.

By combining two-frequency excitation with 1H NMR STEAM spectroscopy, it is possible to measure two volumes of interest simultaneously without an increase in measuring time compared to single-volume STEAM. Spatial selectivity and spectral resolution of this approach are demonstrated for test solutions and for human 1H NMR brain spectroscopy. First results with a tumor patient are also presented.

Brain↗
PubMed1990

Analysis of glycogen storage disease by in vivo 13C NMR: comparison of normal volunteers with a patient.

Broadband proton-decoupled natural abundance 13C spectra of the human calf, liver, and head were obtained from normal volunteers and a patient with glycogen type IIIA storage disease. Two concentric and coplanar surface coils of diameters 8.0 cm and 13.0 cm were used for 13C (at 16.0 MHz) and 1H (at 63.6 MHz), respectively. A WALTZ-8 sequence lead to homogeneous decoupling over a large volume. In addition to lipid resonances a variety of other metabolite resonances could be resolved. The glycogen concentration in the muscle and the liver of normal volunteers varied considerably depending on dietary preparation and physical exercise. The glycogen level in the liver and the calf of a patient with glycogen type IIIA storage disease was increased by a factor of 2-3 compared to normal, well-trained volunteers. Proton-decoupled 13C spectra of human head are reported for the first time. The spectra are dominated by lipid resonances but an additional resonance at 54.0 ppm is clearly visible. The proton-decoupled 13C head spectrum of a patient with glycogen type IIIA storage disease revealed additional resonances between 71.0 and 85.0 ppm.

Abdominal Muscles↗
PubMed1990

Interaction of phospholipids with Ca2+ ions. On the role of the phospholipid head groups.

Neutral phospholipids play an important role in Ca2+ binding to biomembranes, in particular if the membrane carries a net negative surface charge due to charged lipids or proteins. The concentration of Ca2+ ions in the plane of the phospholipid head groups can be enhanced by at least two orders of magnitude compared to bulk solution. Ca2+ binding furthermore changes the orientation of the phospholipid head groups which is accompanied by variations of the local membrane dipole potential of the order of 10(5) V/cm. Such high electric fields could entail conformational changes of membrane-bound proteins and the Ca2(+)-induced reorientation of the lipid dipoles could thus play a regulatory role in membrane function.

Calcium↗
PubMed1989

Electric charge effects on phospholipid headgroups. Phosphatidylcholine in mixtures with cationic and anionic amphiphiles.

The influence of electric surface charges on the polar headgroups and the hydrocarbon region of phospholipid membranes was studied by mixing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with charged amphiphiles. A positive surface charge was generated with dialkyldimethylammonium salts and a negative surface charge with dialkyl phosphates. The POPC:amphiphile ratio and hence the surface charge density could be varied over a large range since stable liquid-crystalline bilayers were obtained even for the pure amphiphiles in water. POPC was selectively deuterated at both methylene segments of the choline moiety and at the cis double bond of the oleic acyl chain. Additional experiments were carried out with 1,2-dipalmitoyl-rac-glycero-3-phosphocholine labeled at the C-2 position of the glycerol backbone. Deuterium, phosphorus, and nitrogen-14 nuclear magnetic resonance (NMR) spectra were recorded for liquid-crystalline bilayers with varying concentrations of amphiphiles. Although the hydrocarbon region and the glycerol backbone were not significantly influenced by the addition of amphiphiles, very large perturbations of the phosphocholine headgroup were observed. Qualitatively, these results were similar to those observed previously with other cationic and anionic molecules and suggest that the electric surface charge is the essential driving force in changing the phospholipid headgroup orientation and conformation. While the P-N dipole is approximately parallel to the membrane surface in the pure phospholipid membrane, the addition of a positively charged amphiphile or the binding of cationic molecules moves the N+ end of the dipole toward the water phase, changing the orientation of the phosphate segment by more than 30 degrees at the highest amphiphile concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Ampholyte Mixtures↗
PubMed1989

Interaction of melittin with phosphatidylcholine membranes. Binding isotherm and lipid head-group conformation.

The binding of melittin to nonsonicated bilayer membranes composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine was studied with an ultracentrifugation assay and with 2H and 31P nuclear magnetic resonance. Melittin binding could best be described by a partition equilibrium with Kp = (2.1 +/- 0.2) X 10(3) M-1, measuring the binding isotherm in the concentration range of 0-100 microM melittin and taking into account electrostatic effects by means of the Gouy-Chapman theory. This partition coefficient is smaller than that deduced for small sonicated vesicles and attests to the tighter lipid packing in the nonsonicated bilayers. Deuterium magnetic resonance revealed a conformational change of the phosphocholine head group upon melittin binding. The quadrupole splittings of the alpha and beta segments of the choline head group varied linearly with the amount of bound melittin but in opposite directions; i.e., the alpha splitting decreased, and the beta splitting increased. This conformational change is not specific to melittin but is a response of the phosphocholine head group to positive membrane surface charges in general. Quantitatively, melittin is one of the most efficient head-group modulators, the efficiency per unit charge comparable to that of charged local anesthetics or hydrophobic ions.

Bee Venoms↗
PubMed1989

Monoclonal antibody-coated magnetite particles as contrast agents in magnetic resonance imaging of tumors.

A highly specific and powerful magnetic resonance imaging contrast agent has been prepared by coating magnetite (Fe3O4) particles with monoclonal antibodies directed against a tumor antigen. The preparation maintains both the immunoreactivity of the monoclonal antibody and the full relaxing capability of the magnetite particle. MRI image contrast by spin-echo methods can be easily induced in a concentration range of 1-10 nM of the antibody-coated magnetite particles.

Animals↗
PubMed1988

Anion binding to neutral and positively charged lipid membranes.

Aqueous anion binding to bilayer membranes consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was investigated by using deuterium and phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy. Only those anions that exhibit chaotropic properties showed significant binding to POPC membranes. A detailed investigation of thiocyanate binding to neutral POPC and to positively charged mixed POPC/dihexadecyldimethylammonium bromide (DHDMAB) (8:2 mol/mol) membranes revealed changes in the 2H NMR quadrupole splittings from POPC specifically deuteriated at either the alpha-segment or the beta-segment of the choline head group which were consistent with a progressive accumulation of excess negative charge at the membrane surface with increasing SCN- concentration. Both the 2H and 31P NMR spectra indicated the presence of fluid lipids in a bilayer configuration up to at least 1.0 M NaSCN with no indication of any phase separation of lipid domains. Calibration of the relationship between the change in the 2H NMR quadrupole splitting and the amount of SCN- binding provided thiocyanate binding isotherms. At a given SCN- concentration the positively charged membranes bound levels of SCN- 3 times that of the neutral membranes. The binding isotherms were analyzed by considering both the electrostatic and the chemical equilibrium contributions to SCN- binding. Electrostatic considerations were accounted for by using the Gouy-Chapman theory. For 100% POPC membranes as well as for mixed POPC/DHDMAB (8:2 mol/mol) membranes the thiocyanate binding up to concentrations of 100 mM was characterized by a partition equilibrium with an association constant of K approximately 1.4 +/- 0.3 M-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Anions↗
PubMed1988

In situ metabolism of 1,omega medium chain dicarboxylic acids in the liver of intact rats as detected by 13C and 1H NMR.

The hepatic metabolism of 1,omega-dodecanedioic acid, a physiologically relevant representative of the medium-chain dicarboxylic acid family, has been studied by a combination of in vivo and in vitro 13C and 1H NMR spectroscopic techniques. Rats in different nutritional or hormonal situations were infused with [1,12-13C2]- or [1,2,11,12-13C4]dodecanedioic acid, and the kinetics of 13C label appearance as well as the final relative concentrations of metabolic products were measured noninvasively in the liver of the intact rat by 13C NMR spectroscopy. Perchloric acid and chloroform/methanol extracts of liver biopsies obtained at the end of the infusion period were further analyzed by high resolution 13C NMR and one-dimensional and two-dimensional COSY and J-resolved 1H NMR. [1-13C]- and [1,2-13C2]adipic acids were the main end products of the in vivo metabolism of [1,12-13C2]- or [1,2,11,12-13C4]dodecanedioic acids, respectively, indicating that the beta-oxidation pathway of medium-chain dicarboxylic acids proceeds in situ monodirectionally. [1-13C]Adipic acid, the main product of peroxisomal beta-oxidation, could also be detected in situ. This finding, together with the in vivo and in vitro absence of signals characteristic of intramitochondrial oxidation of [1-13C]acetyl-coenzyme A, provide a strong evidence supporting a predominant contribution of the peroxisomal beta-oxidation system to the overall oxidation of these compounds in vivo. Homonuclear two-dimensional COSY 1H NMR spectra of acid extracts from rat liver provided a convenient method of analyzing the metabolic repercussions of dicarboxylic acid accumulation, revealing a decrease in the hepatic concentration of beta-hydroxybutyrate and an accumulation of adipic acid and the amino acid L-lysine.

Adipates↗
PubMed1988

Deuterium NMR studies of the interactions of polyhydroxyl compounds and of glycolipids with lipid model membranes.

The physical properties of bilayers composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in the presence of four water-soluble polyhydroxyl compounds, trehalose, sorbitol, glycerol, and ethyleneglycol, and three neutral glycolipids - monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and nonhydroxy fattyacyl-cerebrosides (NHFA-Cer) - were investigated using 2H-NMR. All four polyhydroxyl compounds induced small, but comparable concentration-dependent changes in the choline headgroup conformation which were consistent with the presence of a small negative charge being conferred upon the bilayer surface. The latter may be explained by dipolar interactions brought about by changes in the long-range order of the water layer at the membrane surface. Trehalose had a small ordering effect on the hydrophobic interior of the membrane while ethyleneglycol induced a disordering, at both the head group level and in the hydrophobic interior. The presence of high amounts of carbohydrate at the membrane surface was ensured when POPC was mixed with various proportions of one of three glycolipids, MGDG, DGDG and NHFA-Cer. In these cases the conformation of the choline headgroup was only marginally altered when not masked by macroscopic phase changes. The headgroup conformational changes observed in the presence of any of the above-mentioned compounds were modest in comparison to the effects induced by charged substances.

Ethylene Glycol↗
PubMed1988

Partitioning of local anesthetics into membranes: surface charge effects monitored by the phospholipid head-group.

The binding of the charged form of two local anesthetics, dibucaine and etidocaine, to bilayers composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was measured simultaneously with ultraviolet spectroscopy and deuterium magnetic resonance. Because of their amphiphilic molecular structure, both drugs intercalate between the lipid molecules, increasing the surface area and imparting a positive electric charge onto the membrane. The ultraviolet (UV) binding isotherms were therefore analyzed in terms of a model which specifically took into account the bilayer expansion as well as the charge-induced concentration variations near the membrane surface. By formulating a quantitative expression for the change in surface area upon drug intercalation and combining it with the Gouy-Chapman theory, the binding of charged dibucaine and etidocaine to the lipid membrane was best described by a partition equilibrium, with surface partition coefficients of 660 +/- 80 M-1 and 11 +/- 2 M-1 for dibucaine and etidocaine, respectively (pH 5.5, 0.1 M NaCl/50 mM buffer). Deuterium magnetic resonance demonstrated further that the binding of drug changed the head-group conformation of the lipid molecules. Invoking the intercalation model, a linear variation of the deuterium quadrupole splittings of the choline segments with the surface charge density was observed, suggesting that the phosphocholine head-group may act as a 'molecular electrometer' with respect to surface charges.

Acetanilides↗
PubMed1988

Dynamic properties of gramicidin A in phospholipid membranes.

The flexibility of the tryptophan side chains of gramicidin A and the rotational diffusion of the peptide in methanolic solution and in three membrane systems were studied with deuterium nuclear magnetic resonance (NMR). Gramicidin A was selectively deuterated at the aromatic ring systems of its four tryptophan side chains. In methanolic solution, the tryptophan residues remained immobile and served as a probe for the overall rotation of the peptide. The experimentally determined rotational correlation time of tau c = 0.6 X 10(-9) s was consistent with the formation of gramicidin A dimers. For gramicidin A incorporated into bilayer membranes, quite different results were obtained depending on the chemical and physical nature of the lipids employed. When mixed with 1-palmitoyl-sn-glycero-3-phosphocholine (LPPC) at a stoichiometric lipid:peptide ratio of 4:1, gramicidin A induced the formation of stable bilayer membranes in which the lipids were highly fluid. In contrast, the gramicidin A molecules of this membrane remained completely static over a large temperature interval, suggesting strong protein-protein interactions. The peptide molecules appeared to form a rigid two-dimensional lattice in which the interstitial spaces were filled with fluidlike lipids. When gramicidin A was incorporated into bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine or 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) above the lipid phase transition, the deuterium NMR spectra were motionally narrowed, indicating large-amplitude rotational fluctuations. From the measurement of the quadrupole echo relaxation time, a rotational correlation time of 2 X 10(-7) s was estimated, leading to a membrane viscosity of 1-2 P if the rotational unit was assumed to be a gramicidin A dimer. (ABSTRACT TRUNCATED AT 250 WORDS)

Dimyristoylphosphatidylcholine↗
PubMed1987

Calcium binding to mixed cardiolipin-phosphatidylcholine bilayers as studied by deuterium nuclear magnetic resonance.

Calcium binding to bilayer membranes containing cardiolipin (CDL) mixed with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was investigated by using phosphorus-31 and deuterium nuclear magnetic resonance (NMR) spectroscopy. The destabilizing effect of Ca2+ on CDL bilayers, including the formation of hexagonal H11 and isotropic phases, was eliminated when CDL was mixed with sufficiently large proportion of POPC. Thus, for the mixture CDL-POPC (1:9 M/M), 31P NMR spectra retained a line shape typical of fluid bilayer lipids even in the presence of 1.0 M Ca2+. Specifically head-group-deuteriated CDL or POPC showed in this mixture 2H NMR spectra indicating that both lipids remained in a fluidlike bilayer at Ca2+ concentrations up to 1.0 M. Any phase separation of Ca2-CDL clusters could be excluded. The residence time of Ca2+ at an individual head group binding site was shorter than 10(-6) s. The deuterium quadrupole splitting, delta nu Q, of POPC deuteriated at the alpha-methylene segment of the choline head group was found to be linearly related to the number of bound calcium ions, X2, for the CDL-POPC (1:9 M/M) mixture. The effective surface charge density, sigma, could be determined from the measured amount of bound Ca2+. Subsequently, the surface potential, psi 0, and the concentration of free Ca2+ ions at the plane of ion binding were calculated by employing the Gouy-Chapman theory. Various possible models of the equilibrium binding of Ca2+ could then be tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1987

Deuterium nuclear magnetic resonance studies on the plasmalogens and the glycerol acetals of plasmalogens of Clostridium butyricum and Clostridium beijerinckii.

Deuterium nuclear magnetic resonance was used to investigate the structure of different lipid fractions isolated from the anaerobic bacteria Clostridium butyricum and Clostridium beijerinckii. The fractions isolated from C. butyricum were (1) phosphatidylethanolamine/plasmenylethanolamine and (2) the glycerol acetal of plasmenylethanolamine, and from C. beijerinckii similar fractions containing principally (1) phosphatidyl-N-monomethylethanolamine, along with its plasmalogen, and (2) the glycerol acetal of this plasmalogen were isolated. The third fraction from both species consisted largely of the acidic lipids phosphatidylglycerol and cardiolipin along with plasmalogen forms of these lipids. Palmitic acid with deuterium labels at C-2, C-3, or C-4 or oleic acid with deuterium labels at C-2 and C-9,10 was added to the growth medium and incorporated to various extents in the lipid fractions. Biochemical analysis showed that palmitic acid and oleic acid were preferentially bound to the sn-2 and sn-1 positions, respectively, of the glycerol backbone when both fatty acids were added to the medium. From the 2H NMR spectra, the hydrocarbon chain ordering near the lipid-water interface could be determined and appeared to be similar for all three lipid fractions. The deuterium quadrupole splitting and order parameter were low at the C-2 segment and increased by almost a factor of 2 at positions C-3 and C-4 for cells fed with deuterated palmitic acid along with unlabeled oleic acid. These results agree with previous findings on pure diacyl lipids in which the sn-2 chain was found to adopt a bent conformation at the carbon segment C-2. However, two unusual quadrupole splittings could be detected for the plasmalogens.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetals↗
PubMed1987

Structure and dynamics of plasmalogen model membranes containing cholesterol: a deuterium NMR study.

Deuterium nuclear magnetic resonance (2H-NMR) was used to investigate the structure and dynamics of the sn-2 hydrocarbon chain of semi-synthetical choline and ethanolamine plasmalogen in bilayers containing 0, 30, and 50 mol% cholesterol. The deuterium NMR spectra of the choline plasmalogen yielded well-resolved quadrupolar splittings which could be assigned to the corresponding hydrocarbon chain deuterons. The sn-2 acyl chain was found to adopt a similar conformation as observed in the corresponding diacyl phospholipid, however, the flexibility at the level of the C-2 methylene segment of the plasmalogen was increased. Deuterium NMR spectra of bilayers composed of the ethanolamine plasmalogen yielded quadrupolar splittings of the C-2 segment much larger than those of the corresponding diacyl lipids, suggesting that the sn-2 chain is oriented perpendicular to the membrane surface at all segments. Cholesterol increased the ordering of the choline plasmalogen acyl chain to the same extent as in diacyl lipid bilayers. T1 relaxation time measurements demonstrated only minor dynamical differences between choline plasmalogen and diacyl lipids in model membranes.

Cholesterol↗