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  • Artikel  (49)
  • Polymer and Materials Science  (37)
  • Animals  (12)
  • 1990-1994  (49)
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  • Artikel  (49)
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  • 1
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    Atomic structure of the cubic core of the pyruvate dehydrogenase multienzyme complex (1992)
    American Association for the Advancement of Science (AAAS)
    Details
    Publikationsdatum: 1992-03-20
    Beschreibung: The highly symmetric pyruvate dehydrogenase multienzyme complexes have molecular masses ranging from 5 to 10 million daltons. They consist of numerous copies of three different enzymes: pyruvate dehydrogenase, dihydrolipoyl transacetylase, and lipoamide dehydrogenase. The three-dimensional crystal structure of the catalytic domain of Azotobacter vinelandii dihydrolipoyl transacetylase has been determined at 2.6 angstrom (A) resolution. Eight trimers assemble as a hollow truncated cube with an edge of 125 A, forming the core of the multienzyme complex. Coenzyme A must enter the 29 A long active site channel from the inside of the cube, and lipoamide must enter from the outside. The trimer of the catalytic domain of dihydrolipoyl transacetylase has a topology identical to chloramphenicol acetyl transferase. The atomic structure of the 24-subunit cube core provides a framework for understanding all pyruvate dehydrogenase and related multienzyme complexes.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mattevi, A -- Obmolova, G -- Schulze, E -- Kalk, K H -- Westphal, A H -- de Kok, A -- Hol, W G -- New York, N.Y. -- Science. 1992 Mar 20;255(5051):1544-50.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry, University of Groningen, The Netherlands.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/1549782" target="_blank"〉PubMed〈/a〉
    Schlagwort(e): Amino Acid Sequence ; Animals ; Azotobacter vinelandii/enzymology ; Chloramphenicol O-Acetyltransferase/genetics ; Humans ; Models, Molecular ; Molecular Sequence Data ; Molecular Structure ; Pyruvate Dehydrogenase Complex/*chemistry/genetics ; Sequence Homology, Nucleic Acid
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 2
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    Inclusion of thermal motion in crystallographic structures by restrained molecular dynamics (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publikationsdatum: 1990-09-07
    Beschreibung: A protein crystal structure is usually described by one single structure, which largely omits the dynamical behavior of the molecule. A molecular dynamics method with a time-averaged crystallographic restraint was used to overcome this limitation. This method yields an ensemble of structures in which all possible thermal motions are allowed, that is, in additional to isotropic distributions, anisotropic and anharmonic positional distributions occur as well. In the case of bovine pancreatic phospholipase A2, this description markedly improves agreement with the observed x-ray diffraction data compared to the results of the classical one-model structure description. Time-averaged crystallographically restrained molecular dynamics reveals large mobilities in the loops involved in lipid bilayer association.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gros, P -- van Gunsteren, W F -- Hol, W G -- New York, N.Y. -- Science. 1990 Sep 7;249(4973):1149-52.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉BIOSON Research Institute, University of Groningen, The Netherlands.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2396108" target="_blank"〉PubMed〈/a〉
    Schlagwort(e): Animals ; Cattle ; Crystallography ; Hot Temperature ; Models, Molecular ; Motion ; *Phospholipases ; *Phospholipases A ; Phospholipases A2 ; Protein Conformation ; X-Ray Diffraction
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 3
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    EGF receptor and erbB-2 tyrosine kinase domains confer cell specificity for mitogenic signaling (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publikationsdatum: 1990-04-06
    Beschreibung: The epidermal growth factor (EGF) receptor (EGFR) can efficiently couple with mitogenic signaling pathways when it is transfected into interleukin-3 (IL-3)-dependent 32D hematopoietic cells. When expression vectors for erbB-2, which is structurally related to EGFR, or its truncated counterpart, delta NerbB-2, were introduced into 32D cells, neither was capable of inducing proliferation. This was despite overexpression and constitutive tyrosine kinase activity of their products at levels associated with potent transformation of fibroblast target cells. Thus, EGFR and erbB-2 couple with distinct mitogenic signaling pathways. The region responsible for the specificity of intracellular signal transduction was localized to a 270-amino acid stretch encompassing their respective tyrosine kinase domains. Thus, tissue- or cell-specific regulation of growth factor receptor signaling can occur at a point after the initial interaction of growth factor with receptor. Such specificity in signal transduction may account for the selection of certain oncogenes in some malignancies.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Di Fiore, P P -- Segatto, O -- Taylor, W G -- Aaronson, S A -- Pierce, J H -- New York, N.Y. -- Science. 1990 Apr 6;248(4951):79-83.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2181668" target="_blank"〉PubMed〈/a〉
    Schlagwort(e): Animals ; Base Sequence ; Cell Division ; Cell Line ; DNA/genetics ; DNA, Recombinant ; Fibroblasts/cytology/metabolism ; Gene Expression ; Genetic Vectors ; Hematopoietic Stem Cells/cytology/metabolism ; Immunoblotting ; Mice ; *Mitogens ; Molecular Sequence Data ; Protein-Tyrosine Kinases/genetics/*physiology ; Proto-Oncogene Proteins/genetics/*physiology ; Receptor, Epidermal Growth Factor/genetics/*physiology ; Sequence Homology, Nucleic Acid ; Signal Transduction ; Transfection
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 4
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    Visualization of quantal synaptic transmission by dendritic calcium imaging (1994)
    American Association for the Advancement of Science (AAAS)
    Details
    Publikationsdatum: 1994-01-28
    Beschreibung: As changes in synaptic strength are thought to be critical for learning and memory, it would be useful to monitor the activity of individual identified synapses on mammalian central neurons. Calcium imaging of cortical neurons grown in primary culture was used to visualize the activation of individual postsynaptic elements by miniature excitatory synaptic currents elicited by spontaneous quantal release. This approach revealed that the probability of spontaneous activity differed among synapses on the same dendrite. Furthermore, synapses that undergo changes in activity induced by glutamate or phorbol ester treatment were identified.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Murphy, T H -- Baraban, J M -- Wier, W G -- Blatter, L A -- New York, N.Y. -- Science. 1994 Jan 28;263(5146):529-32.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/7904774" target="_blank"〉PubMed〈/a〉
    Schlagwort(e): Animals ; Calcium/*metabolism ; Cells, Cultured ; Cerebral Cortex ; Dendrites/*metabolism ; Glutamates/pharmacology ; Glutamic Acid ; Kinetics ; Microelectrodes ; Neuronal Plasticity ; Neurons/*physiology ; Phorbol Esters/pharmacology ; Rats ; Receptors, N-Methyl-D-Aspartate/physiology ; Synapses/*physiology ; *Synaptic Transmission ; Tetrodotoxin/pharmacology
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 5
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    CD26 antigen and HIV fusion? (1994)
    American Association for the Advancement of Science (AAAS)
    Details
    Publikationsdatum: 1994-05-20
    Beschreibung: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Broder, C C -- Nussbaum, O -- Gutheil, W G -- Bachovchin, W W -- Berger, E A -- New York, N.Y. -- Science. 1994 May 20;264(5162):1156-9; author reply 1162-5.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/7909959" target="_blank"〉PubMed〈/a〉
    Schlagwort(e): Animals ; Antigens, CD4/*physiology ; Antigens, Differentiation, T-Lymphocyte/*physiology ; Base Sequence ; *Cell Fusion ; Cell Line ; Dipeptidyl Peptidase 4 ; Gene Products, env/*physiology ; Giant Cells/physiology ; HIV-1/*physiology ; Humans ; Hybrid Cells ; Molecular Sequence Data
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 6
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    Regulation of the Ets-related transcription factor Elf-1 by binding to the retinoblastoma protein (1993)
    American Association for the Advancement of Science (AAAS)
    Details
    Publikationsdatum: 1993-05-28
    Beschreibung: The retinoblastoma gene product (Rb) is a nuclear phosphoprotein that regulates cell cycle progression. Elf-1 is a lymphoid-specific Ets transcription factor that regulates inducible gene expression during T cell activation. In this report, it is demonstrated that Elf-1 contains a sequence motif that is highly related to the Rb binding sites of several viral oncoproteins and binds to the pocket region of Rb both in vitro and in vivo. Elf-1 binds exclusively to the underphosphorylated form of Rb and fails to bind to Rb mutants derived from patients with retinoblastoma. Co-immunoprecipitation experiments demonstrated an association between Elf-1 and Rb in resting normal human T cells. After T cell activation, the phosphorylation of Rb results in the release of Elf-1, which is correlated temporally with the activation of Elf-1-mediated transcription. Overexpression of a phosphorylation-defective form of Rb inhibited Elf-1-dependent transcription during T cell activation. These results demonstrate that Rb interacts specifically with a lineage-restricted Ets transcription factor. This regulated interaction may be important for the coordination of lineage-specific effector functions such as lymphokine production with cell cycle progression in activated T cells.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wang, C Y -- Petryniak, B -- Thompson, C B -- Kaelin, W G -- Leiden, J M -- R01 AI29673-01/AI/NIAID NIH HHS/ -- New York, N.Y. -- Science. 1993 May 28;260(5112):1330-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Medicine, University of Chicago, IL 60637.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8493578" target="_blank"〉PubMed〈/a〉
    Schlagwort(e): Amino Acid Sequence ; Animals ; Base Sequence ; Binding Sites ; Cell Cycle ; Cell Line ; DNA-Binding Proteins/chemistry/*metabolism ; Eye Neoplasms/genetics ; Humans ; Lymphocyte Activation ; Molecular Sequence Data ; Mutation ; Oligodeoxyribonucleotides ; Phosphorylation ; Recombinant Fusion Proteins/metabolism ; Retinoblastoma/genetics ; Retinoblastoma Protein/*metabolism ; T-Lymphocytes/immunology/*metabolism ; Transcription Factors/chemistry/*metabolism ; Transcription, Genetic
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 7
    Digitale Medien
    Digitale Medien
    Polyisobutylene-containing block polymers by sequential monomer addition. I. The living carbocationic polymerization of styrenePaper XL in the series “Living Carbocationic Polymerization.” (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 421-426 
    Details
    ISSN: 0887-624X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The living carbocationic polymerisation of styrene (St) has been investigated by the 2-chloro-2,4,4-trimethylpentane (TMPCI)/TiCl4 initiating system in the presence of various additives such as electron pair donors (EDs) and the proton trap 2,6-di-tert-butylpyridine (DtBP) by the use of the mixed solvent CH3Cl/methyl-cyclohexane (MCHx) (40/60 v/v) at -80°C under conventional laboratory conditions. The TMPCl/TiCl4 system in the absence of additives produces ill-defined bimodal molecular weight distribution (MWD) polymers. Much better defined polystyrenes (PSt) can be obtained in the presence of EDs, such as N,N-dimethylacetamide (DMA) and hexamethylphosphoramide (HMPA). Monomer depletion should be avoided to prevent intra- or intermolecular alkylation yielding indanyl end groups or branched polymers, respectively. In the combined presence of an ED and the proton trap, i.e., DMA + DtBP, the living polymerization of St has been achieved and thus the foundations for the carbocationic synthesis of PSt block polymers by sequential monomer addition have been laid.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1991.080290315
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  • 8
    Digitale Medien
    Digitale Medien
    Polyisobutylene-containing block polymers by sequential monomer addition. II. Polystyrene-polyisobutylene-polystyrene triblock polymers: Synthesis, characterization, and physical propertiesPaper XLI in the series “Living Carbocationic Polymerization.” (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 427-435 
    Details
    ISSN: 0887-624X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: New linear and three-arm star thermoplastic elastomers (TPEs) comprising a rubbery polysobutylene (PIB) midblock flanked by glass polystyrene (PSt) blocks have been synthesized by living carbocationic polymerization in the presence of select additives by sequential monomer addition. First, isobutylene (IB) was polymerized by bi- and trifunctional tert-ether (dicumyl- and tricumyl methoxy) initiators in conjunction with TiCl4 conintiator in CH3Cl/methylcyclohexane (MeCHx) (40/60 v/v) solvent mixtures at -80°C. After the living, narrow molecular weight, distribution PIB (M̄w/M̄n = 1.1-1.2) has reached the desired molecular weight, styrene (St) together with an electron pair donor (ED) and a proton trap (di-tert-butylpyridine, DtBP) were added to block PSt from the living chain ends. Uncontrolled initiation by protic impurities that produces PSt contamination is prevented by the use of DtBP. PSt-PIB-PSt blocks obtained in the absence of additives are contaminated by homopolymer and /or diblocks due to inefficient blocking and initiation by protic impurities, and exhibit poor physical properties. In contrast in the presence of the strong ED N,N-dimethylacetamide (DMA) and DtBP the blocking of St from living PIB chain occurs efficiently and block copolymers exhibiting good mechanical properties can be prepared. Virgin TPEs can be repeatedly compression molded without deterioration of physical properties. The products exhibit a low and a high temperature Tg characteristic of phase separated PIB and PSt domains. Transmission electron microscopy of linear triblocks containing ∼ 34 wt % PSt also indicates microphase separation and suggests PSt rods dispersed in a PIB matrix.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1991.080290316
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  • 9
    Digitale Medien
    Digitale Medien
    Polyisobutylene-containing block polymers by sequential monomer addition. IV. New triblock thermoplastic elastomers comprising high Tg styrenic glassy segments: Synthesis, characterization and physical propertiesFor Parts I and II of this series, see Ref. 2; For Part III, see Polym. Prepr., 23 (1), 310 (1991); Part LXV of the series of Living Carbocationic Polymerization. (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 41-48 
    Details
    ISSN: 0887-624X
    Schlagwort(e): thermoplastic elastomer ; carbocationic polymerization ; polyisobutylene ; living polymerization ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: New linear triblock thermoplastic elastomers (TPEs) comprising a rubbery polyisobutylene (PIB) midblock flanked by two glassy endblocks of various styrenic polymers have been synthesized by living carbocationic polymerization by sequential monomer addition. First isobutylene (IB) was polymerized by a bifunctional tert-ether (dicumyl methyl ether) initiator in conjunction with TiCl4 coinitiator in CH3Cl/methylcyclohexane (MeCHx) (40/60 v/v) solvent mixtures at -80°C. After the living narrow molecular weight distribution PIB midblock ($\[\bar M_n\]$ = 1.1-1.2) has reached the desired molecular weight, the styrenic monomers together with an electron pair donor (ED) and a proton trap (di-tert-butylpyridine, DtBP) were added to start the blocking of the glassy segments from the living ⊕PIB⊕ chain ends. While p-methylstyrene (pMeSt), p-t-butylstyrene (ptBuSt) and indene (In) gave essentially 100% blocking to the corresponding glassy endblocks, the blocking of 2,4,6-trimethylstyrene (TMeSt) and α-methylstyrene (αMeSt) were ineffective. Uncontrolled initiation by protic impurities was prevented by the use of DtBP. In the simultaneous presence of DtBP and the strong ED N,N-dimethylacetamide (DMA), TPEs with good mechanical properties (10-20 MPa tensile strength, 300-600% elongation) were prepared. The products exhibit a low and a high temperature Tg characteristic of phase separated rubbery and glassy domains. The service temperature of these new TPEs exceeds that of PSt-PIB-PSt triblock copolymers due to the higher Tgs (PpMeSt = 108, PptBuSt = 142 and PIn = 220-240°C) of the outer blocks. The Tg of the glassy blocks can be regulated by copolymerizing two styrene derivatives; a triblock copolymer with outer blocks of poly(pt-butylstyrene-co-indene) showed a single glassy transition Tg = +165°C, i.e., in between that of PptBuSt and PIn. Virgin TPEs have been repeatedly compression molded without deterioration of physical properties. The high melt flow index obtained with a TPE containing PptBuSt endblocks suggests superior processability relative to those with PSt end-blocks. The tensile strength retention at 60°C of the former TPE is far superior to that of a PSt-PIB-PSt triblock of similar composition.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1992.080300105
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  • 10
    Digitale Medien
    Digitale Medien
    The effect of blending temperature, composition, and shear rate on PET/Vectra A900 LCP blend viscosity and morphology (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 43 (1991), S. 329-349 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The rheological and morphological properties of several melt-blended compositions of poly(ethylene terephthalate) (PET) and Vectra A900 liquid crystalline polyester were investigated, using blending temperature, composition, and shear rate as variables. Rheological behavior was determined at several shear rates on an Instron capillary rheometer at 300°C, and three-dimensional surface plots of the results were prepared, detailing the effect on melt viscosity of changes in the variables. Scanning electron microscopy was used to examine the internal morphology of selected samples. In the preparation of melt blends containing an isotropic and anisotropic polymer, blending temperature and composition both influence the resulting morphology. These effects are accentuated during extrusion of the blends at low shear rates and diminished at high shear rates.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1991.070430211
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