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  • 1
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    Crystal structure of a catalytic antibody with a serine protease active site (1994)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1994-08-19
    Description: The three-dimensional structure of an unusually active hydrolytic antibody with a phosphonate transition state analog (hapten) bound to the active site has been solved to 2.5 A resolution. The antibody (17E8) catalyzes the hydrolysis of norleucine and methionine phenyl esters and is selective for amino acid esters that have the natural alpha-carbon L configuration. A plot of the pH-dependence of the antibody-catalyzed reaction is bell-shaped with an activity maximum at pH 9.5; experiments on mechanism lend support to the formation of a covalent acyl-antibody intermediate. The structural and kinetic data are complementary and support a hydrolytic mechanism for the antibody that is remarkably similar to that of the serine proteases. The antibody active site contains a Ser-His dyad structure proximal to the phosphorous atom of the bound hapten that resembles two of the three components of the Ser-His-Asp catalytic triad of serine proteases. The antibody active site also contains a Lys residue to stabilize oxyanion formation, and a hydrophobic binding pocket for specific substrate recognition of norleucine and methionine side chains. The structure identifies active site residues that mediate catalysis and suggests specific mutations that may improve the catalytic efficiency of the antibody. This high resolution structure of a catalytic antibody-hapten complex shows that antibodies can converge on active site structures that have arisen through natural enzyme evolution.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zhou, G W -- Guo, J -- Huang, W -- Fletterick, R J -- Scanlan, T S -- DK39304/DK/NIDDK NIH HHS/ -- New York, N.Y. -- Science. 1994 Aug 19;265(5175):1059-64.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0448.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8066444" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Antibodies, Catalytic/*chemistry/immunology/metabolism ; Binding Sites ; Computer Graphics ; Crystallization ; Crystallography, X-Ray ; Haptens/metabolism ; Hydrogen Bonding ; Hydrogen-Ion Concentration ; Hydrolysis ; Models, Molecular ; Molecular Sequence Data ; Protein Conformation ; Serine Endopeptidases/*chemistry/metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
    Electronic Resource
    Electronic Resource
    A study of the properties and topological trapping of cyclic poly(dimethylsiloxane) in poly(2,6-dimethyl-1,4-phenylene oxide) networks (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 1807-1812 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polymeric catenanes have been made from poly(2,6-dimethyl-1,4-phenylene oxide) crosslinked in the presence of several, paucidisperse poly(dimethylsiloxane) cyclics of varying degrees of polymerization. The fraction of cyclic threaded or captured by the polymer network increases as the degree polymerization of the cyclic increases in good agreement with the crude estimates of Frisch and Wasserman. Thermal analysis and electron micrographs reveal microphone separation in all of the polymeric catenanes; with PDMS domain size around 10-50 μ. Most of the catenanes exhibit a lower tensile strength to break than the pure crosslinked PPO.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080280712
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  • 3
    Electronic Resource
    Electronic Resource
    FTIR investigation of cross-linking and isomerization reactions of acetylene-terminated polyimide and polyisoimide oligomers (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 2005-2017 
    Details
    ISSN: 0887-6266
    Keywords: FTIR spectroscopy ; acetylene-terminated polyisoimide ; acetylene-terminated polyimide ; isoimide-imide isomerization ; cross-linking reaction ; thermal curing process ; flexibility effect ; cross-linking effect ; rate constant ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The interrelationship between the cross-linking and isoimide-imide isomerization reactions of oligomeric isoimides and imides was investigated using FTIR spectroscopy. It was found that cross-linking of the acetylene units of Thermid IP-600 retarded the local rearrangement of the isoimide to imide conversion of Thermid IP-600 compared with an aniline-terminated analog, decreasing the rate constant by a factor of about 2. The increased flexibility of both the isoimide (Thermid IP-600) and imide (Thermid FA-700) oligomers increased the cross-linking rate of the acetylene end groups by a factor of 4 and 2, respectively, over that of the more rigid imide oligomer (MC-600). With increasing conversion of the isoimide to imide linkages in Thermid IP-600, the kinetic parameters, Eα and in A, for the cross-linking reaction of this oligomer became the same as those for the oligomeric imide, Thermid MC-600. © 1994 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090321207
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  • 4
    Electronic Resource
    Electronic Resource
    Probe diffusion in polystyrene/toluene solutions (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 2629-2649 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The technique of forced Rayleigh scattering has been used to measure the tracer diffusion coefficient, Dt, for two photochromic dyes, azobenzene and Aberchrome 540, in polystyrene / toluene solutions, as a function of polymer concentration (79-90% by weight) and temperature (-15-+60°C). The dye diffusivity can be scaled quantitatively to the solvent diffusivity, permitting direct application of the Vrentas-Duda free volume predictions for binary systems. However, the scaling factors are not in agreement with the model assumptions. The temperature and concentration dependence of Dt above the solution glass transition temperature, Tgs, is in good agreement with the model, without any freely adjustable parameters. The value of Dt at Tgs is a very strong function of concentration, increasing by a factor of 103 as the polymer concentration is reduced from 90 to 80%; this is also in quantitative agreement with the model. It is demonstrated that the temperature dependence of Dt exhibits a distinct break in the vicinity of Tgs, with both the existence and the character of the break in qualitative agreement with the extension of the Vrentas-Duda approach to glassy solutions. However, a fundamental difficulty in the calculation of the polymer contribution to the solution free volume at temperatures well below the bulk polymer Tg is exposed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1990.090281311
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of damage on fatigue crack propagation in polystyrene (1990)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 1303-1308 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this paper we examine a conventional approach to correlate the fatigue crack growth rate with fracture mechanics parameters such as stress intensity factor or elastic energy release rate. To simulate a complex loading history we grow a fatigue crack in a vicinity of a hole in a single edge notched specimen under tension-tension. It is found that the correlation between the crack speed and stress intensity factor, etc. may exist only for limited experimental conditions. In general, fatigue crack growth is inseparable from the evolution of the damage zone preceding the crack, and damage evolution parameters should enter constitutive equations of fatigue crack growth. The essential role of the damage zone in determining the crack trajectory and speed is demonstrated.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760302007
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  • 6
    Electronic Resource
    Electronic Resource
    SERS study of the conformational transition of the ordering of lipid molecules deposited on a silver electrode (1992)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 23 (1992), S. 425-430 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dipalmitoylphosphatidylcholine lipid molecules adsorbed on a silver electrode were found to exhibit a conformational phase transition when investigated by means of surface-enhanced Raman scattering. The observed order-to-disorder transition of the hydrocarbon chain is voltage dependent and exhibits hysteresis phenomena. It is suggested that the adsorption of lipid molecules occurs at the phosphocholine moiety and the kinetic process for the transition involves a voltage-induced conformational change of the head group.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250230802
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