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  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1347-1349 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 363-375 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The atomic coordinates from the crystal structure of a hexasaccharide complex accommodating a zigzag polyiodide [ W. Hinrichs, G. Büttner, M. Steifa, Ch. Betzel, V. Zabel, B. Pfannemüller, and W. Saenger (1987) Science Vol. 238, pp. 205-208; W. Hinrichs and W. Saenger (1990) Journal of the American Chemical Society, Vol. 112, pp. 2789-2796 ] served to construct an antiparallel-stranded amylose double helix with a 5 Å wide central cavity. Using our methodology for the energetic optimization of polymer structures in the internal/ helical variable space [ H. Sklenar, R. Lavery, and B. Pullman (1986) Journal of Biomolecular Structure Dynamics, Vol. 3, pp. 967-987, 989-1014; 1015-1031], we have calculated a theoretical counterpart of this idealized double helix by constraining the helical twist and rise to their experimental values (-45° and 2.33 Å, respectively). Applying the same constraints to the parallel-stranded duplex, this also leads to a low-energy structure with wide central cavity. It is considered as an alternative model to accommodate iodine as observed in the starch-iodine complex.Release of the helical constraints leads to left-handed antiparallel- and parallel-stranded double helices, respectively, with narrow central cavities. Both structures have very similar helix parameters and correspond, in their main characteristics, to the experimentally derived parallel-stranded structure of amylose in starch (6 residues per turn and a pitch height of about 21 Å). The intramolecular energy calculated for the optimized antiparallel-stranded amylose double helix is comparable to that of the parallel-stranded structure. This result raises the question why parallel-stranded amylose seems to be favored in nature. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 3
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cytostatic drug 6-azauridine is converted in vivo to 6-azauridine-5′-phosphate (z6Urd-5′-P), which blocks the enzyme orotidine-5′-phosphate decarboxylase (Ord-5′-Pdecase) and therefore inhibits the de novo production of uridine-5′-phosphate (Urd-5′-P). In order to relate the structure and function of z6Urd-5′-P, it was crystallized as trihydrate, space group P212121 with a = 20.615 Å, b = 6.265 Å, c = 11.881 Å, and the structure established by Patterson methods. Atomic parameters were refined by full-matrix least-squares methods to R = 0.066 using 1638 counter measured x-ray data. The ribose of z6Urd-5′-P is in a twisted C(2′)-exo, C(3′)endo conformation, the heterocycle is in extreme anti position with angle N(6)-N(1)-C(1′)-O(4′) at 86.3°, and the orientation about the C(4′)-C(5′) bond is gauche, trans in contrast to gauche, gauche found for all the other 5′-ribonucleotides. Conformational energy calculations show that z6Urd-5′-P may adopt an extreme anti conformation not allowed to Urd-5′-P, and they also predict the same unusual trans, gauche conformation about the C(4′)-C(5′) bond in orotidine-5′-phosphate (Ord-5′-P) and in z6Urd-5′-P, which renders the distances O(2)…O(5′) in z6Urd-5′-P and O(7)…O(5′) in Ord-5′-P comparable. On this basis the function of z6Urd-5′-P as an Ord-5′-Pdecase inhibitor can be explained as being due to its structural similarity with the substrate Ord-5′-P and further clarifies the inhibitory action of 5′-nucleotides bearing the heterocycles oxipurinol, xanthine, or allopurinol [J. A. Fyfe, R. L. Miller, and T. A. Krenitsky, J. Biol. Chem. 248, 3801 (1973)]. With this in mind, new inhibitors for Ord-5′-Pdecase may be designed.
    Additional Material: 10 Ill.
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