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Biomedical subjects

W Kreutz

Publications and source records attributed to W Kreutz.

At least 37 records · Page 2Linked to original sources
PubMed1990

Structure of human low-density lipoprotein subfractions, determined by X-ray small-angle scattering.

The structure of low-density lipoprotein (LDL) particles from three different density ranges (LDL-1: d = 1.006-1.031 g/ml; LDL-3: d = 1.034-1.037 g/ml; LDL-6: d = 1.044-1.063 g/ml) was determined by X-ray small-angle scattering. By using a theoretical particle model, which accounted for the polydispersity of the samples, we were able to obtain fits of the scattering intensity that were inside the noise interval of the measured intensity. The assumption of deviations from radial symmetry is not supported by our data. This implies a spread-out conformation of the apolipoprotein B (apoB) molecule, which appears to be localized in the outer surface shell. A globular structure is not consistent with our data. Furthermore, different models exist concerning the structure of the cholesterol ester core below the phase transition temperature. The electron density data suggest an arrangement in which the steroid moieties are localized at average radii of 3.2 and 6.4 nm. Model calculations show that packing problems can only be avoided if approximately half of the acyl chains of each shell are pointing towards the center of the particle, the other half towards the surface. This arrangement of the acyl chains has never been proposed before. The LDL particles of different density classes differ mainly with respect to the size of the core but also with respect to the width of the surface shells. Model calculations show that the size of different LDL particles can be accurately predicted from the compositional data.

Apolipoproteins B↗
PubMed1990

High resolution 13C-solid state NMR of bacteriorhodopsin: assignment of specific aspartic acids and structural implications of single site mutations.

Three mutant strains of Halobacterium sp. GRB with the site of mutation in the bacterioopsin gene (PM 326: Asp96----Asn; PM 374: Asp96----Gly; PM 384: Asp85----Glu) were grown in a synthetic medium containing (4-13C)-Asp. The mutant bacteriorhodopsins labeled with (4-13C)-Asp (37%-45%), and owing to the metabolism of Halobacteria also with (11-13C)-Trp (50%-100%), were isolated as purple membranes and 13C Solid State Magic Angle Sample Spinning (MASS) Nuclear Magnetic Resonance (NMR) spectra of the samples were taken. The Asp96 mutants lacked the signal at 171.3 ppm which was previously assigned to a protonated internal Asp (Engelhard et al. 1989a). This observation supports the conclusion that Asp96 is protonated in the ground state. PM 384 (Asp85----Glu) has an absorption maximum at 610 nm. It can be converted into a purple form (lambda max = 540 nm) by treatment with a detergent (CHAPSO). The NMR-spectra of these two species differ from each other and from the wild type. The intensity of the resonance at 173 ppm in the wild type spectrum is reduced in both forms of the mutant protein. It is probable that this signal is caused by Asp85. The amino acid changes result not only in a perturbation of their direct environment but also effects on Trp residues and the chromophore protein interaction can be observed.

Aspartic Acid↗
PubMed1990

Identification of precipitable Ca2+ by electron spectroscopic imaging and electron energy loss spectroscopy in the organ of Corti of the guinea pig.

Ca2+ cations were precipitated with potassium antimonate in the cochlea of the guinea pig, and the formed precipitates were localized by electron microscopy using either elastically or inelastically scattered electrons. The elemental composition of the precipitates was determined by electron spectroscopic imaging (ESI) and electron energy loss spectroscopy (EELS). It was found that calcium, antimony and oxygen were the dominating elements in the precipitates formed in different cell types in the inner ear.

Animals↗
PubMed1989

Magic angle sample spinning 13C nuclear magnetic resonance of isotopically labeled bacteriorhodopsin.

Bacteriorhodopsin (bR), the light-driven proton pump protein from Halobacterium halobium, was biosynthetically labeled with [4-13C]Asp. The incorporation yield was 48%. The magic angle sample spinning (MASS) 13C nuclear magnetic resonance (NMR) spectrum of this sample revealed six different peaks superimposed on a broad band of naturally abundant peptide-bond 13C. Two of the six carbonyl signals can be attributed to internal-protonated Asp carboxyl groups, one of which might be Asp115. An additional resonance at 110 ppm can be associated with the C-11 carbon of Trp, indicating an unusual biosynthetic pathway of this amino acid in Halobacterium halobium. Similar measurements performed on papain-treated purple membrane which lacks the C-terminal tail display two new intense signals at 178 and 178.9 ppm. If the same spectrum is taken without cross-polarization, these signals do not decrease or disappear. On the basis of their intensities and their chemical shifts, one can assign in addition to the C-terminal Asp four Asp residues facing the cytoplasmic phase. In native bR, at least two of these form a salt-bridge-like bond which also might include the C-terminal tail. These experiments not only provide data about the chemical environment of the Asp residues within the hydrophobic core of bacteriorhodopsin but also yield information about the interactions between surface components.

Amino Acid Sequence↗
PubMed1989

Crystallization and preliminary X-ray analysis of porin from Rhodobacter capsulatus.

Porin monomers of the phototrophic bacterium Rhodobacter capsulatus were purified. Crystals were obtained from a solution of porin solubilized with the detergent octyltetraoxyethylene within 5 days using the vapor phase equilibration technique. The crystals were rhombohedral with an edge length of 0.4 mm. The space group was trigonal R3 with unit cell constants of a = b = 95 A, c = 147 A. Reflexions were observed to 3.2 A.

Bacterial Outer Membrane Proteins↗
PubMed1987

Absence of hepatitis after treatment with a pasteurized factor VIII concentrate in patients with hemophilia and no previous transfusions.

Post-transfusion hepatitis is frequent among patients with hemophilia who are treated with concentrated factor VIII prepared from pooled plasma, especially if it is obtained from paid donors. In 26 patients with hemophilia A or von Willebrand's disease who had not been treated with blood or any blood product and hence were highly susceptible to the development of post-transfusion hepatitis, we infused 32 batches of a factor VIII concentrate that had been produced from large pools of human plasma (collected from paid plasmapheresis donors) and then heated in solution at 60 degrees C for 10 hours before final lyophilization. Patients were examined clinically and serologically over a period of 12 months after the first infusion of the pasteurized concentrate. Neither hepatitis nor serologic signs of other viral infections were observed. The hemostatic effectiveness of the concentrate appeared to be satisfactory relative to untreated concentrates.

Adolescent↗
PubMed1985

Light-driven protonation changes of internal aspartic acids of bacteriorhodopsin: an investigation by static and time-resolved infrared difference spectroscopy using [4-13C]aspartic acid labeled purple membrane.

The molecular events during the photocycle of bacteriorhodopsin have been studied by the method of time-resolved and static infrared difference spectroscopy. Characteristic spectral changes involving the C=O stretching vibration of protonated carboxylic groups were detected. To identify the corresponding groups with either glutamic or aspartic acid, BR was selectively labeled with [4-13C]aspartic acid. An incorporation of ca. 70% was obtained. The comparison of the difference spectra in the region of the CO2- stretching vibrations of labeled and unlabeled BR indicates that ionized aspartic acids are influenced during the photocycle, the earliest effect being observed already at the K610 intermediate. Taken together, the results provide evidence that four internal aspartic acids undergo protonation changes and that one glutamic acid, remaining protonated, is disturbed. The results are discussed in relation to the various aspects of the proton pumping mechanism, such as retinal isomerization, charge separation, pK changes, and proton pathway.

Aspartic Acid↗
PubMed1983

Changes in HDL subfractions after a single, extended episode of physical exercise.

In order to investigate the changes in HDL subfractions induced by a single period of extended physical exercise, 9 endurance-trained adults were examined before and 6 min, 1 and 6 h after a 30 km cross-country race. In contrast to less evident changes in the concentrations of total HDL, apolipoprotein A-I and A-II, there were significant changes in HDL subfractions. Resting levels of protein and cholesterol content of the HDL subfractions 1-3 increased (subfraction 1, density gradient 1.093: 1.68 +/- 0.58 to 3.24 +/- 0.86 mmol/1 cholesterol, P less than 0.001), while the concentrations in HDL subfractions 11-12 decreased proportionately (subfraction 12, density gradient 1.142: 3.68 +/- 0.81 to 2.19 +/- 0.22 mmol/1 cholesterol, P less than 0.001). The results suggest that physical exercise induces an increased formation of HDL particles of lower density from HDL particles of higher density. It was concluded that this formation is related to the catabolism of triglyceride-rich lipoproteins in the post-exercise period.

Cholesterol↗
PubMed1982

Temperature-induced vertical shift of proteins in membranes.

Thermotropic changes in the transverse order of microsomal membranes isolated from Tetrahymena are revealed by low-angle X-ray diffraction. These are correlated with the lateral order of the membrane lipids by wide-angle X-ray diffraction. Upon lowering the temperature from 28 degrees C to 2 degrees C, the Bragg period of the membrane stack reveals an abrupt increase of approximately 3.1 nm at approximately 19 degrees C, which is reversible upon reheating to 28 degrees C. This is coupled with an alteration in the electron density profile, revealing a shift of mass from the hydrophobic core towards one of the two hydrophilic surfaces. Between 35 degrees C and 0 degrees C, the membrane lipids undergo a broad, thermotropic "two-stage" liquid crystalline in equilibrium crystalline phase separation with a "breakpoint" at approximately 18 degrees C. This breakpoint signals an abrupt lipid redistribution, presumably due to a change in the composition of the two coexisting liquid crystalline and crystalline lipid phases. We conclude: (1) the temperature-induced mass shift reflects a shift in the transverse partition of proteins in membranes; (2) this is triggered by an abrupt lipid redistribution occurring during a broad liquid crystalline in equilibrium crystalline phase separation.

Fatty Acids↗
PubMed1982

Thermotropic 'two-stage' liquid crystalline equilibrium crystalline lipid phase separation in microsomal membranes.

The effect of temperature on native microsomal membrane vesicles isolated from Tetrahymena is investigated by wide angle X-ray diffraction. A 4.2 reflection, typical for lipids in the crystalline state, can be recorded in the temperature range between 0 degree C and 35 degrees C. Quantitative evaluation of this reflection reveals a broad thermotropic 'two-stage' liquid crystalline equilibrium crystalline lipid phase separation with a 'breakpoint' at approx. 18 degrees C. This 'breakpoint' coincides with the emergency of lipid-protein segregations in endomembranes of intact Tetrahymena cells as previously visualized by freeze-etch electron microscopy.

Animals↗
PubMed1982

Interrelationships of ion transport in rat submaxillary duct epithelium.

The transport of Na+, K+, Cl-, and HCO3(-) across the epithelium of the rat submaxillary salivary duct is postulated to be due to the coupling of the basolateral Na+-K+-ATPase with various ion transport systems in the luminal and basolateral membranes. Na+ reabsorption depends on the presence of a rheogenic (Na+ conductance) and an electroneutral (Na+:H exchange) pathway, both of which are sensitive to amiloride. K+ secretion is postulated to be mediated by a K+: H+ antiport, coupling between Na+ reabsorption and K+ secretion, thus depending on local H+ ion concentration. The ratio between electroneutral Na+ influx and K+ efflux, therefore, determines the rate of HCO3(-) secretion. In the absence of Na+ influx, although K+ efflux falls, HCO3(-) secretion rises to a value equal to that of K+ secretion. The maintenance of K+ secretion in the absence of luminal Na+ requires an additional Na+-entry step across the basolateral membrane, also postulated to be due to Na+:H+ exchange.

Animals↗
PubMed1981

Evaluation of the electron density profile of the frog rod outer segment disc-membrane in vivo using x-ray diffraction.

The structure of the rod outer segment disc-membrane in vivo was studied by X-ray low-angle scattering. The experiments were made on frogs under narcosis. Diffraction patterns corresponding to a resolution of 1.5 nm could be obtained from the membrane stacks of the rod outer segment discs. For the analysis of the measured diffraction pattern a new special computer procedure was elaborated. Among other generalizations of the theory, it was taken into account that the electron densities in the inter- and intra-disc spaces differ from the mean electron density of the whole stack. The consideration of this possibility, together with an exact experimental measurement of the isotrope background scattering, led to a mathematically unique solution. The calculated electron density profile apparently is a distinct asymmetric bilayer. The electron density of the side of the membrane which is in contact with the disc lumen is higher than the electron density on the side in contact with the cytoplasm. Therefore, a localization of rhodopsin or of other high molecular proteins mainly on the cytoplasmatic edge of the membrane can be excluded for the rod outer segment discs in vivo.

Animals↗
PubMed1981

[Cartilage channels of the human patella up to birth].

In the human patella from the 4th month up to the birth were examined contents and surrounding structures of vascular channels. Except the articular area the cartilage of the patella is covered by the perichondrium. From here mesenchym and blood vessels enter, and penetrate into the cartilage by forming channels. Dependent on the stages of development the construction of cartilage around the channels is different in comparison with other territories. The findings will be compared with the results from the channels in the cartilaginous anlage of different bones.

Cartilage↗
PubMed1980

pH-sensitive liposomes: possible clinical implications.

When pH-sensitive molecules are incorporated into liposomes, drugs can be specifically released from these vesicles by a change of pH in the ambient serum. Liposomes containing the pH-sensitive lipid palmitoyl homocysteine (PHC) were constructed so that the greatest pH differential (6.0 to 7.4) of drug release was obtained near physiological temperature. Such liposomes could be useful clinically if they enable drugs to be targeted to areas of the body in which pH is less than physiological, such as primary tumors and metastases or sites of inflammation and infection.

Antineoplastic Agents↗
PubMed1980

Flash-induced kinetic infrared spectroscopy applied to biochemical systems.

A flash photolysis apparatus with monitoring infrared beam is described allowing measurements of relative transmission changes of 10(-3) in times of a few milliseconds. The investigation of the photodissociation of CO-myoglobin confirms the results obtained by static infrared difference spectroscopy. The application of our method to the rhodopsin/Meta II transition reveals signals which can tentatively be ascribed to the disappearance of the C = C-band of the protonated N-retinylidene Schiff base in rhodopsin. The developed method will be compared with other existing methods of kinetic vibronic spectroscopy such as kinetic resonance Raman spectroscopy and kinetic Fourier infrared spectroscopy.

Animals↗