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  • 1990-1994  (4)
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Materialart
Erscheinungszeitraum
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  • 1
    Digitale Medien
    Digitale Medien
    Internal symmetry of the molecular chaperone cpn60 (GroEL) determined by X-ray crystallography (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 591-595 
    Details
    ISSN: 1399-0047
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The Escherichia coli molecular chaperone cpn60 oligomer, [cpn60]14, also called GroEL, has been crystallized and examined by X-ray crystallography and self-rotation function calculations. The crystals show unit-cell dimensions a = 143.3, b = 154.6 and c = 265 Å, with α = 82, β = 95 and γ = 107°. The space group is P1 and crystals diffract to 7 Å. X-ray analysis shows that the oligomer has one sevenfold symmetry axis and seven twofold axes that are all perpendicular to the sevenfold. The symmetry suggests that [cpn60]24 consists of two heptamers, [cpn60]7, stacked on top of each other. The orientations of the symmetry axes of the two independent [cpn60]14 oligomers in the triclinic unit cell have been determined relative to the crystallographic axes. The two oligomers in the unit cell are arranged side-by- side, but the second oligomer is rotated 26° around the sevenfold axis relative to the first oligomer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0907444993014349
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  • 2
    Digitale Medien
    Digitale Medien
    Experience with phase extension and ab initio phase determination in macromolecular crystallography using maximum-entropy methods (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 49 (1993), S. 66-74 
    Details
    ISSN: 1399-0047
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Three procedures, or `tools', have been developed and tested for applying maximum-entropy methods to phase extension and to ab initio phase determination. The phase expander tool has been used in connection with the solution of two previously unknown macromolecular structures. An efficient algorithm for the determination of an electron-density distribution that is everywhere positive and that agrees with observed structure amplitudes (tools II and III) has been used to determine the phases of X-ray diffraction data from recombinant bovine chymosin, a protein with 323 amino-acid residues in the molecular chain, the structure of which was recently determined using replacement methods. By use of the same maximum-entropy methods, the structure amplitudes from the unknown structure of bovine heart creatine kinase, a protein with 381 amino-acid residues, have been phased ab initio to 2.7 Å resolution. The phases of the centric reflections have also been confirmed by a satisfactory solution of the Patterson map of a mercury derivative. The current status of the structure interpretation is presented. This technique has also been applied to a test case where 48 centric reflections from bovine prothrombin fragment 1 data were phased ab initio and subsequently used in the determination of Patterson solutions for a heavy-atom derivative data set.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0907444992009752
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  • 3
    Digitale Medien
    Digitale Medien
    Ab initio phase determination for X-ray diffraction data from crystals of a native protein (1991)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 47 (1991), S. 216-223 
    Details
    ISSN: 1600-5724
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: An efficient algorithm for the determination of an everywhere positive electron-density distribution that agrees with observed structure amplitudes has been used to determine the phases of X-ray diffraction data from recombinant bovine chymosin, a protein with 323 amino-acid residues in the molecular chain whose structure was recently determined using molecular replacement methods. A systematic procedure for testing the signs of centric reflections, using the total entropy of the map as a figure of merit, was used to produce a low-resolution map. The phases of acentric and additional centric reflections were then chosen by adding them to the map with various possible phases and computing the total entropy of the resulting map. Of 159 centric reflections whose phases were chosen by this procedure, 141 had the same phase as in the refined structure. The median absolute phase difference for 1811 acentric reflections was 32°. A map produced from these 1970 reflections, out of 12 346 reflections in the data set, showed a remarkable agreement with the refined structure. This molecule is many times larger than any whose structures have previously been determined without the use of isomorphous replacement, molecular replacement or anomalous dispersion, and the map demonstrates the potential of maximum-entropy methods in macromolecular structure determination.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108767390012077
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  • 4
    Digitale Medien
    Digitale Medien
    Phase improvement in the structure interpretation of fragment TR2C from bull testis calmodulin using combined entropy maximization and solvent flattening (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 46 (1990), S. 209-215 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768189007731
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