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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters A 120 (1987), S. 353-355 
    ISSN: 0375-9601
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 46 (1990), S. 41-46 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A new density modification technique - histogram matching - is being developed with encouraging results. Its application to the known structure of pig 2Zn insulin refines the 6500 1.9 Å MIR phases from a mean error of 60° to one of 46°. With these refined phases as a starting point for phase extension to 1.5 Å, the mean error for the final 13 000 phases is 46°. The original 1.9 Å phases continue to refine during the phase extension to a final mean error of 40°. A comparison is made with similar calculations already published.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 49 (1993), S. 213-222 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The constraints of correct electron-density distribution, solvent flatness, correct local shape of the electron density and equal molecules are combined in an integrated procedure for macromolecular phase refinement and extension. These constraints on electron densities are satisfied simultaneously by solving a system of non-linear equations. The electron-density solution is further filtered by a phase combination procedure. The non-crystallographic symmetry operations are refined by a rotation and translation space search and a least-squares minimization method, thereby reducing the chance of introducing systematic phase errors during averaging. The effect of each constraint on phase refinement and extension is examined. The constraints are found to work synergistically in phase improvement. Test results on 2Zn insulin are presented.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 46 (1990), S. 377-381 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A new method for phase refinement and extension, which combines Sayre's equation with solvent flattening and histogram matching, has been developed. Equations which express electron-density constraints are solved using discrete Fourier transforms to give a new approximation to the electron density. The formulation of the equations is in real space, which allows any set of constraints to be entered directly into the calculation. An application to the known structure of 2Zn insulin refined the 3 Å MIR phases from a mean phase error of 46 to 39° and extended the phases to 2 Å resolution with a mean overall phase error of 57°. Analysis of the phase errors shows that, for the strong reflexions, the new method determines phases with half the mean error of MIR phases.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 258-262 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The crystal structure is described of ribulose 1,5-bisphosphate carboxylase/oxygenase in a new crystal form. This new form (form V) was obtained from a previously known crystal form (form III) through a solid-state phase transition. The solid-state phase transition was brought about by transferring the crystal from a high-salt low-pH mother liquor to a low-salt high-pH synthetic mother liquor. The interplay of electrostatic repulsion and osmotic pressure induced a unit-cell shrinkage of 24 Å along the c axis and expansion of 4 Å along the a and b axes. The space group also changed from I422 to I4. The new crystal form was shown to be more resistant to X-ray radiation damage, which suggests the effect of crystal stabilization by non-penetrating molecules. The structure of ribulose 1,5-bisphosphate carboxylase/oxygenase in the new crystal form is compared with that of the old crystal form.
    Type of Medium: Electronic Resource
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