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  • Artikel  (83)
  • Life Sciences  (83)
  • 2020-2024
  • 1975-1979  (72)
  • 1970-1974  (11)
  • 1940-1944
  • 1
    Digitale Medien
    Digitale Medien
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 9 (1978), S. 253-268 
    ISSN: 0091-7419
    Schlagwort(e): ricin ; lectin ; toxin ; ribosome ; rat liver ; wheat germ ; N-ethylmaleimide ; Life Sciences ; Molecular Cell Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Ricin A chain was radioactively labeled using reductive alkylation, lactoperoxidase catalyzed iodination, and reaction with iodoacetamide or N-ethylmaleimide (NEM). The inhibition of cell-free rat liver protein synthesis by the modified A chains and the ribosome binding characteristics of each of the labeled derivatives was examined. [3H] NEM was found to quantitatively react with the A chain sulfhydryl group normally involved in a disulfide bond with the B chain in intact ricin. Labeling the protein with [3H] NEM had no effect on the in vitro inhibition of protein synthesis by the A chain. [3H] NEM-labeled A chain binds to rat liver ribosomes in a manner which is dependent on the concentrations of NaCl and Mg2+. At optimal Mg2+ concentration (5.5 mM), A chain binding to ribosomes is saturable and fully reversible either by dilution of the reaction mixture or by addition of unlabeled A chain. At 5.5 mM Mg2+, A chain was found to bind to a single site on rat liver ribosomes with a dissociation constant of 6.2 X 10-8 M. [3H] NEM-labeled A chain did not bind to isolated 40S ribosomal subunits and bound to 60S ribosomal subunits with a 1 : 1 molar stoichiometry and a dissociation constant of 2.2 X 10-7 M. The relationship between ribosome binding and A chain inhibition of eucaryotic protein synthesis is discussed.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 5 (1976), S. 453-456 
    ISSN: 0091-7419
    Schlagwort(e): gating currents ; sodium channels ; pore populations ; Life Sciences ; Molecular Cell Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Sodium-channel behavior has been modeled in order to determine the answer to the following question: How large must a population of “on-off” Sodium pores be before the inherently random behavior of the individual channels becomes smoothed to yield the expected gating current-conductance relationships which would be predicted from an infinite pore array? Results of this analysis show that for the “opening” situation, an excellent fit was obtained whenever more than about 10 pores were considered. Significant discrepanciesd were observed in the “Closeing” situation, however, for pore arrays of 50 or less. Marked hysteresis is apparent in the behavior of small pore populations.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 5 (1976), S. 81-90 
    ISSN: 0091-7419
    Schlagwort(e): cytochalasin A and B ; G-actin ; tubulin ; microtubules ; sulfhydryl modification ; convalent modification ; colchicine binding ; Life Sciences ; Molecular Cell Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: The presence of cytochalasin A inhibits the self-assembly of beef brain tubulin and rabbit muscle G-actin in vitro and also decreases the colchicine binding of tubulin. Prior reaction of cytochalasin A with 2-mercaptoethanol destroys its inhibitory effects. It is shown that cytochalasin A exerts its actions by reacting with sulfhydryl groups, possibly causing irreversible structural changes in the proteins. Cytochalasin B does not affect the tubulin assembly reaction.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 9 (1978), S. 427-440 
    ISSN: 0091-7419
    Schlagwort(e): fibrin cross linking ; erythrocyte transamidase ; spectrin ; cytoskeleton ; Life Sciences ; Molecular Cell Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: A rise in the intracellular concentration of Ca2+-ions in human erythrocytes causes the formation of high-molecular-weight membrane protein polymers, cross-linked by γ-glutamyl-∊-lysine side chain bridges. Cross-linking involves proteins at the cytoplasmic side of the membrane (band 4.1, spectrin, and band 3 materials) and the reaction is catalyzed by the intrinsic transglutaminase. This enzyme is regulated by Ca2+-ions and it exists in a latent form in normal cells. The protein polymer, isolated from the membranes of Ca2+-loaded intact human red cells, is heterogeneous in size and may contain as many as 6 moles of γ-glutamyl-∊-lysine cross-links per 100,000 gm of protein.Synthetic compounds, which either compete against the ∊-lysine cross-linking functionalities of the protein substrates (eg, histamine, aminoacetonitrile, cystamine) or directly inactivate the transamidase (eg, cystamine), inhibit the membrane polymerization reaction in intact human erythrocytes. They also interfere with the Ca2+-induced irreversible shape change from discocyte to echinocyte and inhibit the irreversible loss of membrane deformability. Thus, the transamidase-catalyzed production of γ-glutamyl-∊-lysine cross-links in the membrane may be a common denominator in these cellular manifestations.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 4 (1976), S. 121-126 
    ISSN: 0091-7419
    Schlagwort(e): Life Sciences ; Molecular Cell Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: The plant lectin concanavalin A (Con A) specifically inactivates the 5′ -nucleotidase of a plasma membrane-enriched fraction from lactating mammary gland. The lectin also causes an activation of the membrane Mg++ -ATPase, but does not affect galactosyltransferase or alkaline phosphatase. The enzyme perturbations are prevented by α-methylmannoside, an inhibitor of Con A binding, indicating that specific binding to carbohydrate structures rather than nonspecific protein-protein interaction is involved. Solubilization of the 5′ -nucleotidase in detergents (0.2% Triton X-100 or 1% deoxycholate) does not prevent Con A inactivation, indicating that incorporation into the membrane structure is not a requirement for the Con A effect. The results suggest that Con A inactivates the 5′ -nucleotidase by a direct interaction with the enzyme and that this enzyme is a Con A receptor site on the surface of mammary cells.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 5 (1976), S. 591-600 
    ISSN: 0091-7419
    Schlagwort(e): Pyruvate ; hepatoma cells ; cell shape ; macromollecular synthesis ; Life Sciences ; Molecular Cell Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Cells maintained in basal growth medium with 0.2-1.0% serum often require citric acid cycle intermediates for optimal viability. We have found that pyruvate added to minimal growth medium causes cellular flattening and formation of external processes accompanied by increaded DNA synthesis in cultured hepatoma cells (HTC cells).Cells were cultured in plalstic T-flasks (0.5, 1.0, or 2.0 × 106 cells/flask) containing 5 ml medium (90% Eagle's Basal Medium (BME) and 10% Swim's S-77) with various concentrations of fetal calf serum (0.2,0.25, 0.5, 1.0, 2.0, 10%) and either pyruvate (50, 100, 250,500, 1,000μg/ml), or one of: dibutyryl cAMP (DBcAMP) or dibutyryl cGMP (DBcGMP) at 10-3, 10-4, or 10-5 M. At 44-48 hr cultures were pulsed with tritiated thymidine, uridine, or lecucine. Cells became attached to the plastic surface within 24hr. Cells in medium with 0.25 to 2.0% serum had a rounded appearance. With added pyruvate, cellular flattening, process formation, and an increased adherence to the substratum was absorbed. By 48 hr, culture without pyruvate grew in rounded clusters; with pyruvate, cells formed extensive interconnecting processes that appeared loosely attached to the monolayer surface. At the cell densities tested, process formation was maximal with 250 to 500 μg/ml pyruvate. Cytochalasin B blocked flattening and process formation; EDTA (1 mg/ml) caused retraction of processes within 3 min, and a slow dissolution of these structures within cells was observed. DBcAMP or DBcGMP did not induce process formation. Flattening and process foormation in pyruvate-enriched cultures were accompanied by marked stimulation of DNA synthesis and smaller increases in RNA and protein synthesis. Cell number was not affected.These pyruvate-induced changes suggest that alterations in energy metabolism, or precursors that enhance viability and macromolecular synthesis in mammalian cell cultures, may exert marked effects on cellular morphology without corresponding changes in growth of neoplastic liver cells.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 3 (1975), S. 39-50 
    ISSN: 0091-7419
    Schlagwort(e): Life Sciences ; Molecular Cell Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: The porcine neurotubule and its basic subunit were found to be modified in vitro by iodination of amino acids (principally tyrosine) using lactoperoxidase. Iodide ion, H2O2, or lactoperoxidase singly or in any pairwise combination had virtually no effect on neurotubules. However, when all three reagents were present, permitting covalent iodination, it was found that at 0.1 iodotyrosines per tubulin dimer the microtubules unravel to form structures which morphologically resemble strands of protofilaments twisted or wound around each other. These abnormal tubules are stable at room temperature and 4°C. Both monomers of tubulin are labeled to approximately the same extent. Iodinated tubulin (0.1 iodotyrosines/dimer) is unable to assemble in vitro under normal assembly conditions. Heavily iodinated microtubules (8 iodines per tubulin dimer) are similar in morphology to the slightly iodinated structures.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    ISSN: 0091-7419
    Schlagwort(e): Life Sciences ; Molecular Cell Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Recent reports in the literature have indicated a physical association of creatinephosphokinase (CPK) with the tail portion of the myosin molecule. The present paper describes further studies on the interaction of CPK with myosin and myosin fragments, using the techniques of electron paramagnetic resonance (EPR) and nanosecond fluorescence depolarization. From EPR work, spin-labeled CPK appears to interact with myosin, tail-less myosin (heavy meromyosin [HMM]), and myosin heads (subfragment-1 [S1]), the extent of interaction being proportional to the S1 content of myosin or its fragments. Spin-labeled CPK did not evidence interaction with the headless myosin “rods”, with myosin tails (light meromyosin [LMM]), with S2 necks (which connect S1 to the rest of the myosin molecule), or with actin. When a fluorescent dye is directed to the essential ∊-amino group of CPK, nanosecond fluorescence depolarization studies indicate a substantial interaction with myosin, HMM, and S1, but very little with F-actin. When the “fast-reacting” thiol of the S1 moiety or the “essential thiol” of CPK was labeled with either a fluorescent dye or a spin label, no interaction between CPK and myosin (or S1) was detected.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 4 (1976), S. 15-26 
    ISSN: 0091-7419
    Schlagwort(e): Life Sciences ; Molecular Cell Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: The binding, mobility, and mode of cell entry of the plant toxin ricin (or RCAII) were investigated on susceptible and partially resistant murine cell lines. When susceptible cells (SV40-transformed 3T3 fibroblast cells and BW5147 lymphoma cells) were examined, ricin bound rapidly, induced endocytosis, and entered the cell cytoplasm via broken endocytotic vesicles to inhibit cell protein synthesis, as found previously (1). Addition of lactose within 15 min after initial ricin binding prevented toxicity. After this time lactose addition no longer blocked the inhibition of protein synthesis.In a partially resistant lymphoma (BW5147/RCA3) that shows only a slight reduction in the total number of ricin-binding sites, ricin bound rapidly to the cell surface, but was endocytosed significantly less at low ricin doses compared to its parental line, indicating a possible difference in cell surface behavior. The exposed surface proteins on the BW5147 parental and BW5147/RCA3 resistant lines were examined by 125I-labeling utilizing lactoperoxidase-catalyzed iodination. The radiolabeled components were solubilized and separated by slab gel electrophoresis in sodium dodecyl sulfate. Autoradiograms of the slab gels indicated that two surface components of approximately 80,000 and 35,000 mol wt were much less exposed or were missing on the resistant line.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 4 (1976), S. 161-168 
    ISSN: 0091-7419
    Schlagwort(e): Life Sciences ; Molecular Cell Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: We have isolated 5 families of proteins from human red blood cell membranes and characterized their secondary structure by ultraviolet circular dichroism measurements. The protein families were prepared by selective solubilization from ghosts under nondenaturing conditions. We find that the intact ghost has a mean α-helix fraction of 0.37, whereas a low-ionic-strength extract (bands 1, 2, 5, “spectrin”) has a substantially higher helix fraction, 0.55. Further extraction of the ghosts with para-chloromercuribenzoate yields bands 2.1, 4.1, 4.2, and 6; their helix content is only 0.17. Finally, the major intrinsic protein, band 3, was solubilized by a nonionic detergent. Its helix fraction is 0.38.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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