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  • 1
    Electronic Resource
    Electronic Resource
    Perturbation of Trp 138 in T4 lysozyme by mutations at Gln 105 used to correlate changes in structure, stability, solvation, and spectroscopic properties (1993)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 15 (1993), S. 401-412 
    Details
    ISSN: 0887-3585
    Keywords: tryptophan ; fluorescence ; phosphorescence ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In order to correlate between spectroscopic and structural changes in a protein, the environment of Trp 135 in T4 lysozyme was deliberately perturbed by the replacement of Gln 105 with alanine (Q105A), glycine (Q105G), and glutamic acid (Q105E). In wild-type lysozyme, Trp 135 is buried, but the indole nitrogen is hydrogen-bonded to the side-chain of Gln 105. In the Q105G and Q105A mutant structures, the indole nitrogen becomes accessible to solvent. Crystallographic analysis shows that the structures of all of the mutants are similar to wild-type. There are, however, distinct rearrangements of the local solvent structure in response to the new side-chains. There are also small but significant changes in the relative orientations of the two domains of the protein that appear to result from a series of small, concerted movements of side-chains adjacent to residue 105. Evaluation of the fluorescence and phosphorescence of the mutant proteins in terms of their observed three-dimensional structures shows that large spectral changes do not necessarily imply large changes in structure or in static solvent accessibility. Increases in polar relaxation about the excited state of tryptophan may be the result of only small increases in local dynamics or solvent exposure. 1H-NMR was also used to monitor the effects of the substitutions on Trp 138. In Q105E, but not in Q105G, Q105A and WT, the Hε1 chemical shift of Trp 138 is very pH-dependent, apparently reflecting the titration of Glu 105 which has a spectroscopically determined pKa of 6.0. The elevation of the pKa of Glu 105 in Q105E is also reflected in the pH dependence of the stability of this mutant. © 1993 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340150407
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  • 2
    Electronic Resource
    Electronic Resource
    Tensile and bend relationships of several surgical needle materials (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Biomaterials 4 (1993), S. 161-167 
    Details
    ISSN: 1045-4861
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Four stainless steel alloys, commonly used for surgical needles were tensile and bend tested. The materials included: ASTM 42000, ASTM 45500, ASTM 30200, and a Fe-12Cr-8.5Ni-3.2Mo-1.9Ti alloy. Small diameter wires in a wide range of strength levels were produced using various heat treatments and/or cold drawing. Samples from each processing condition were tensile and bend tested. Calculated yield moment and ultimate moment were determined using tensile yield strength, the flexural formula (M(y) = σ(y) I/C), and the shape factor for circular cross sections (M(u)/M(y) = 1.7). A deviation was observed between the theoretically calculated yield moment and a 2° offset measured yield moment. This was expected because moment-strain diagrams provide only an approximation of yield moment due to the gradual departure from linearity. The 2° offset yield was termed the surgical yield because it represents the strain at which a surgical needle would start to lose functionality. A nonlinear relationship (R) was observed between measured and calculated values. The relationship (R) proved to be a function of cold work by wire drawing as measured by the change in wire length (ΔL), R = a - b * In(ΔL). This suggests that engineers selecting materials for bending applications such as surgical needles cannot use tensile data alone to predict bend strength. Processing history must also be known. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jab.770040208
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  • 3
    Electronic Resource
    Electronic Resource
    Melt viscosity increase during rheological testing of poly(phenylene sulfide) (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 50 (1993), S. 1903-1907 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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: Poly(phenylene sulfide) (PPS) made via the melt polymerization of p-diiodobenzene and sulfur has previously been reported to increase in melt viscosity with time during rheological testing. Analysis of the oligomer from cleavage of PPS chains at the disulfide bonds via solution in 1-chloronaphthalene demonstrated that the disulfide content of the polymer decreased with rheological testing time. DSC of the polymer before and after rheological testing in combination with the Tcc and Tm of the chain fragments after the dissolution/cleavage in 1-chloronaphthalene showed that many samples exhibited primarily chain extension rather than chain branching, whereas for many others, some degree of chain branching occurred. This is currently only qualitatively understood. Chain branching as the exclusive mechanism of melt viscosity increase during rheological testing appears untenable in light of the Tm, in particular, of the chain fragments and also the polymer prior to chain cleavage. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070501106
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