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  • 1
    Digitale Medien
    Digitale Medien
    Positioning a protein molecule in the asymmetric unit using very low order reflections and packing restraints (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 32 (1999), S. 530-535 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: A method for predicting the position of protein molecules in the unit cell is presented. This prediction is based on the structure-factor amplitudes of the very low order reflections and packing considerations. With very low resolution data, the calculated electron density is very blurred, such that a protein molecule may well be approximated as a sphere. A sphere with the same volume as the unknown protein was translated in small (2–3 Å) steps in the corresponding Cheshire cell until maximum overlap between the amplitudes calculated from the sphere and the true protein structure was found. A molecular packing can be calculated to restrain the allowable regions. This makes the positioning of the protein molecule even more reliable. Structure factors of the ten or so lowest resolution reflections were calculated with a sphere at the best position. These structure factors agreed closely with those of the true protein structure. The translation algorithm has been successfully tested for 16 proteins. For 12 out of 16 proteins tested, the position of the centre of the molecule was correctly predicted to within 5 Å. A qualitative deduction of deviations from the spherical model can be gained by comparing structure factors from the spherical model and the true protein. The very low resolution phasing obtained by this method may be used as powerful starting set for phase-extension methods such as maximum entropy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889899003209
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  • 2
    Digitale Medien
    Digitale Medien
    The protein content in crystals and packing coefficients in different space groups (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 789-790 
    Details
    ISSN: 1399-0047
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: A precise way of estimating the packing coefficient, i.e. the ratio between the protein and unit-cell volume, or solvent content in protein crystals is given. At present, the solvent content is not given for most proteins in the Protein Data Bank and in many cases where it is given the values are dubious. The mean density of proteins in the crystalline form is around 1.22 g cm−3, not 1.35 g cm−3 as usually stated. This is equivalent to 19.5 Å3 per non-H atom. A statistical investigation of the average protein content and packing coefficient in different space groups is presented. The packing coefficients are generally higher in the most frequently occurring space groups than in the uncommon space groups. There is also a remarkable difference in frequency distribution for enantiomorphous pairs of space groups.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0907444900005163
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  • 3
    Digitale Medien
    Digitale Medien
    New evidence from the South China Sea for an abrupt termination of the last glacial period (1988)
    [s.l.] : Nature Publishing Group
    Nature 333 (1988), S. 156-158 
    Details
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] In their classic study of sediments from the northern Atlantic, Ruddiman et al1 demonstrated that the warming of surface waters associated with the end of the last glacial (termination I) and with penultimate glaciation (termination II) occurred very rapidly. A radiocarbon chronology for one of ...
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1038/333156a0
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  • 4
    Digitale Medien
    Digitale Medien
    Limits on the ventilation rate for the deep ocean over the last 12000 years (1986)
    Springer
    Climate dynamics 1 (1986), S. 53-62 
    Details
    ISSN: 1432-0894
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract In this paper we present accelerator radiocarbon measurements on hand picked benthic and planktonic foraminifera separated from two deep sea cores raised from the South China Sea. From the benthic-planktonic age differences we are able to place limits on the extent to which the ventilation rate of the deep Pacific Ocean has changed over the last 12000 years. While much work remains to be done before any definitive answers for the global oceans can be given, these results on cores with sedimentation rates suitably high to avoid major corrections for bioturbation effects suggest that the ventilation rate of the deep Pacific Ocean has remained nearly the same throughout Holocene time. Further, there is no suggestion that the rate was slower during the period of major glacial retreat. These results confirm that the changes in atmospheric14C/C ratio over the last 10000 years owe their origin to radiocarbon production rate changes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01277046
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