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  • 1
    ISSN: 1432-2048
    Schlagwort(e): Heat stress ; Chaperonin ; Lycopersicon ; Mitochondrion ; Solanum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A 68-kDa heat-stress protein (HSP68) has been purified from cell-suspension cultures of tomato (Lycopersicon peruvianum L.). Antibodies raised against HSP68 cross-react with the Escherichia coli heat-stress protein DnaK. HSP68 was found to be a hydrophilic, ATP-binding protein. Immunological analysis of subcellular fractions and immunogold-labelling of ultrathin sections showed consistently that HSP68 is localized in the mitochondrial matrix. In-vitro translation experiments indicated that HSP68 is synthesized as a precursor protein. Immunoscreening of cDNA libraries from tomato and potato (Solanum tuberosum L.) led to the isolation of corresponding cDNA clones. The deduced amino-acid sequences show strong relationships to the DnaK-like proteins from bacteria and organelles of eukaryotic cells. The protein HSP68 is constitutively expressed, but its synthesis is increased during heat stress in all cells of higher plantes investigated so far.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 47 (1991), S. 47-50 
    ISSN: 1420-9071
    Schlagwort(e): Cold receptor ; periodic discharge pattern ; transducer process ; low-threshold calcium channel
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary The regular periodic activity patterns of mammalian cold receptors have been quantitatively studied. Analysis of the timing of either single impulses or impulse groups demonstrated that the periodic receptor process is maintained independently of impulse generation and continues to operate under conditions when afferent impulses are not initiated. These results imply that the underlying conductances must be operational at threshold potentials related to impulse generation. In addition to temperature, the periodic process is considerably sensitive to calcium, which affects mainly the probability of impulse generation during each cycle. Reduction of external calcium and application of calcium entry blockers with relative selectivity for low-threshold calcium channels are similarly effective in modulating cold receptor activity. The data imply the existence of a low-threshold calcium conductance at the sensory terminal.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Current genetics 20 (1991), S. 405-410 
    ISSN: 1432-0983
    Schlagwort(e): ADP/ATP translocator ; Mitochondria ; Presequence ; Gene expression
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The ADP/ATP translocator is an abundant protein of the mitochondrial inner membrane, which in fungi and mammals is synthesized without a presequence. Here we report that the translocator from potato has an amino-terminal extension which may function in mitochondrial targeting. Several cDNA clones encoding the nucleotide sequence of the ADP/ATP translocator have been isolated from potato leaf and tuber cDNA libraries constructed in lambda phages. Only one class of cDNA clones was found but possibly different translocator genes are expressed in other tissues. High levels of transcripts for the translocator are found in all tissues analysed. Sequence determination of the complete insert of one of the clones reveals a long open reading frame of 1158 bp encoding a protein of 386 amino acids corresponding to a calculated molecular weight of 42 kDa. In contrast, the ADP/ATP translocator proteins from fungi and mammals are significantly smaller. Comparison of the Neurospora translocator with the potato protein shows about 75% sequence homology, being confined to the region after amino acid 85 of the potato polypeptide. Antibodies directed against the fungal translocator recognize a protein of 30 kDa in the inner membrane of potato mitochondria, suggesting that the mature protein has a similar size as the translocators from fungi and mammals. Thus, the additional segment of the potato ADP/ATP translocator forms an amino-terminal extension which may be involved in the import of the protein into plant mitochondria.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of environmental contamination and toxicology 47 (1991), S. 374-380 
    ISSN: 1432-0800
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik , Medizin
    Materialart: Digitale Medien
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  • 5
    ISSN: 1279-8517
    Schlagwort(e): Paranasal sinuses, anatomy ; Paranasal sinuses, childhood ; Paranasal sinuses, MR-Imaging ; Sphenoid bone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Résumé Afin de démontrer les aspects fondamentaux du développement du sinus sphénoïdal pendant l'enfance, nous avons revu l'aspect en IRM du sinus sphénoïdal de 401 patients agés de moins de 15 ans. L'étude de la moelle osseuse, le développement de la pneumatisation, la croissance et le cloisonnement du sinus sphénoïdal ont été explorés en séquences pondérées en T1 et en T2. Le sinus sphénoïdal se présente, en séquence pondérée en T1, avec un signal faible et uniforme (moelle osseuse rouge) chez tous les enfants agés de moins de 4 mois. Ce signal hypo-intense devient hyper-intense (transformation de la moelle osseuse) à partir du 4 ème mois. Le début de la pneumatisation est noté à 13–15 mois. A l'âge de 43–48 mois, la partie antérieure du sinus sphénoïdal est pneumatisée chez 85 % des enfants. La pneumatisation est complète chez tous les patients agés de plus de 10 ans. La croissance dans chaque direction de l'espace est caractéristique. L'apparition d'un septum médian est observée à une fréquence variable par tranche d'âge, avec un maximum de 77 %. Les variations existent dans 4,5 % à 20 % des cas. La connaissance de ce phénomène peut servir de référence pour évaluer le développement normal et anormal du sinus sphénoïdal et être d'un grand intérêt dans le diagnostic et le traitement des affections du sinus sphénoïdal et des régions voisines chez l'enfant.
    Notizen: Summary To obtain baseline standards of normal age-related development of the sphenoid sinus during childhood magnetic resonance images of the sphenoid sinus in 401 patients less than 15 years old were reviewed. T1-weighted sagittal and T2-weighted axial scans were evaluated for bone marrow conversion, development of pneumatization, spatial enlargement and septation of the sphenoid sinus. The sphenoid sinus had a uniformely low signal intensity (red bone marrow) on T1-weighted images in all children less than 4 months old. Signal intensity changes from hypo- to hyperintense (bone marrow conversion) started at age of 4 months. Onset of pneumatization was observed in 12% of the patients at age 13–15 months. By age 43–48 months, 85% of the patients showed pneumatization of the anterior part of the sphenoid bone. Pneumatization was complete in all patients older than 10 years. Enlargement of the sinus showed a characteristic profile in each dimension. Median septation was observed irregularly with age, with a maximum of 77%. Septum variants were noticed between 4.5% and 20%. The recognition of this phenomenon may serve as a reference for evaluating normal and abnormal development of the sphenoid sinus and may be of great value for diagnostic and therapeutic management of pathologic conditions of the child's sphenoid sinus and its surrounds.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Colloid & polymer science 272 (1994), S. 1536-1546 
    ISSN: 1435-1536
    Schlagwort(e): Rheological constitutive equation ; fractional derivatives ; material functions ; relaxation time spectra ; retardation time spectra
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract A rheological constitutive equation for complex polymeric materials is derived starting from a special formulation of the relaxation function. This relaxation function contains six parameters and is divided into three regions: the plateau region, an intermediate power-law region and the terminal region of rapid stress decay. Material functions like the complex modulusG * and the logarithmic density function of the relaxation time spectrum H and of the retardation time spectrum L respectively are derived. Material parameters like the zero shear viscosityη 0 and the equilibrium shear complianceJ e are also calculated. The comparison of the measured dynamic moduli of H-shaped polystyrenes, associating terminally functionalized polyisoprenes and randomly associating polybutadienes with the theoretical predictions of the proposed phenomenological model shows an excellent agreement.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1432-2013
    Schlagwort(e): Catfish ; Ampullary electroreceptors ; Stimulus transduction ; Temperature dependence ; Calcium channels
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The response properties of ampullary electroreceptors have been studied in the catfish Ictalurus nebulosus at skin temperatures between 5 and 35 °C. A unimodal relationship between spontaneous activity and temperature was obtained. Mean (±SEM) peak discharge rate was 57.3 ±1.8 impulses s−1 at 25 ° C; the receptors were active at 5 °C (15.0 impulses s−1) and at 35 °C (31.5 impulses s−1). There were no dynamic responses to temperature changes in either the warming or cooling direction. The shape of the frequency characteristic depended on temperature: the peak of the gain curve shifted to low frequencies at low temperatures. There was a concomitant change of the phase characteristic: the intersection at zero degree phase angle shifted to higher frequencies with an increase of temperature, thus increasing the lead at lower frequencies and decreasing the lag at higher frequencies. Latency after combined excitatory and inhibitory impulse stimulation was temperature dependent, ranging from 16.4 ms (5 °C) to 5.6 ms (35 °C). Application of the specific calcium channel blocker menthol (0.2 mM) suppressed spontaneous activity, the effect becoming more prominent at higher temperatures. Sensitivity to sinusoidal electrical stimulation was also impaired, but to a lesser degree and mainly at lower temperatures. We conclude that the filter properties of the receptor organ can be modelled by a band-pass filter in series with a latency, both of which are temperature dependent. These filter properties might be partially based on the activation kinetics of the tranduction channels.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Rheologica acta 31 (1992), S. 309-322 
    ISSN: 1435-1528
    Schlagwort(e): Linear-viscoelasticity ; material functions ; rheological constitutive equation ; fractional derivative
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Abstract Starting from an analysis of the rheological behavior of the complex modulus predicted by the Cole-Cole formalism, a generalized Cole-Cole ansatz is suggested in order to overcome the related difficulties. The corresponding rheological constitutive equation with fractional derivatives belonging to the generalized Cole-Cole respondance is stated and the characteristic material functions of the linear viscoelasticity theory (like the dynamic modulus and compliance, the relaxation and ratardation functions, the spectra, etc.) are derived. Model predictions of these functions will be compared with experimental results from dynamical measurements and creep data on different polymer systems which show cooperative phenomena (polymeric glasses and gelling systems). One can see that the modified ansatz fits the data very well, in spite of its relative simplicity.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Rheologica acta 30 (1991), S. 523-529 
    ISSN: 1435-1528
    Schlagwort(e): Viscoelasticity ; dissipation in transient flows ; nonisothermal rheological constitutive equations ; dissipation in transient flows
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Abstract Using a power-law ansatz for the temperature dependence of the shear modulus on the level of internal variables, the thermorheological behavior is modeled for viscoelastic fluids of a special group of rheological constitutive equations (rate-type models). The model parameter introduced characterizes thermoelastic contributions. The relation between the model parameter and the physical quantities appearing in deformation processes is discussed. Based on the chosen temperature dependence of the shear modulus, thermodynamically consistent equations like the nonlinear rheological constitutive equation and the temperature equation are derived. The special cases of entirely entropy and energy elastic fluids are also considered. The thermorheological behavior (exo-, α- or endothermal processes) of a viscoelastic fluid in a stress-growth experiment followed by relaxation is analyzed with respect to the model parameter.
    Materialart: Digitale Medien
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  • 10
    ISSN: 1434-6052
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Results on the production of charged hadrons in muon-deuteron and muon-xenon interactions are presented. The data were taken with the E665 spectrometer, which was exposed to the 490 GeV muon beam of the Tevatron at Fermilab. The use of a streamer chamber as vertex detector provides nearly 4π acceptance for charged particles. The μD data are compared with the μXe data in terms of multiplicity distributions, average multiplicities, forward-backward multiplicity correlations, rapidity and transverse momentum distributions and of two-particle rapidity correlations of charged hadrons. The data cover a range of invariant hadronic massesW from 8 to 30 GeV.
    Materialart: Digitale Medien
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