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  • 1
    Electronic Resource
    Electronic Resource
    The crystal structure of the “open” and the “closed” conformation of the flexible loop of trypanosomal triosephosphate isomerase (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 33-49 
    Details
    ISSN: 0887-3585
    Keywords: TIM ; molecular dynamics refinement ; loop movement ; conformational change ; crystal contacts ; sleeping sickness ; suramine ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Triosephosphate isomerase has an important loop near the active site which can exist in a “closed” and in an “open” conformation. Here we describe the structural properties of this “flexible” loop observed in two different structures of trypanosomal triosephosphate isomerase. Trypanosomal triosephosphate isomerase, crystallized in the presence of 2.4 M ammonium sulfate, packs as an asymmetric dimer of 54,000 Da in the crystallographic asymmetric unit. Due to different crystal contacts, peptide 167-180 (the flexible loop of subunit-1) is an open conformation, whereas in subunit-2, this peptide (residues 467-480) is in a closed conformation. In the closed conformation, a hydrogen bond exists between the tip of the loop and a well-defined sulfate ion which is bound to the active site of subunit-2. Such an active site sulfate is not present in subunit-1 due to crystal contacts. When the native (2.4 M ammonium sulfate) crystals are transferred to a sulfate-free mother liquor, the flexible loop of subunit-2 adopts the open conformation. From a closed starting model, this open conformation was discovered through molecular dynamics refinement without manual intervention, despite involving Cα shifts of up to 7 Å. The tip of the loop, residues 472, 473, 474, and 475, moves as a rigid body. Our analysis shows that in this crystal form the flexible loop of subunit-2 faces a solvent channel. Therefore the open and the closed conformations of this flexible loop are virtually unaffected by crystal contacts. The actual observed conformation depends only on the absence or presence of a suitable ligand in the active site.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100105
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  • 2
    Electronic Resource
    Electronic Resource
    Structures of the “open” and “closed” state of trypanosomal triosephosphate isomerase, as observed in a new crystal form: Implications for the reaction mechanism (1993)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 16 (1993), S. 311-326 
    Details
    ISSN: 0887-3585
    Keywords: triosephosphate isomerase ; TIM ; X-ray crystallography ; binding studies ; crystal packing ; conformational change ; reaction mechanism ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The structure of trypanosomal triosephosphate isomerase (TIM)has been solved at a resolution of 2.1Å in a new crystal form grown at pH 8.8 from PEG6000. In this new crystal form (space group C2, cell dimensions 94.8 Å, 48.3 Å, 131.0 Å, 90.0°, 100.3°, 90.0°), TIM is present in a ligand-free state. The asymmetric unit consists of two TIM subunits. Each of these subunits is part of a dimer which is sitting on a crystallographic twofold axis, such that the crystal packing is formed from two TIM dimers in two distinct environments. The two constituent monomers of a given dimer are, therefore, crystallographically equivalent. In the ligand-free state of TIM in this crystal form, the two types of dimer are very similar in structure, with the flexible loops in the “Open” conformation. For one dimer (termed molecule-1), the flexible loop (loop-6) is involved in crystal contacts. Crystals of this type have been used in soaking experiments with 0.4 M ammonium sulphate (studied at 2.4 Å resolution), and with 40 μM phosphoglycolohydroxamate (studied at 2.5 Å resolution). It is found that transfer to 0.4 M ammonuum sulphate (equal to 80 times the Ki of sulphate for TIM), gives rise to significant sulphate binding at the active site of one dimer (termed molecule-2), and less significant binding at the active site of the other. In neither dimer does sulphate induce a “closed” conformation. In a mother liquor containing 40 μM phosphoglycolohydroxamate (equal to 10 times the Ki of phosphoglycolohydroxamate for TIM), an inhibitor molecule binds at the active site of only that dimer of which the flexible loop is free from crystal contacts (molecule-2). In this dimer, it induces a closed conformation. These three structures are compared and discussed with respect to the mode of binding of ligand in the active site as well as with respect to the conformational changes resulting from ligand binding. © 1993 Wiley-Liss, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340160402
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  • 3
    Electronic Resource
    Electronic Resource
    The adaptability of the active site of trypanosomal triosephosphate isomerase as observed in the crystal structures of three different complexes (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 50-69 
    Details
    ISSN: 0887-3585
    Keywords: TIM ; protein-ligand complexes ; water involvement in binding ; drug design ; active site structure ; sleeping sickness ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Crystals of triosephosphate isomerase from Trypanosoma brucei brucei have been used in binding studies with three competitive inhibitors of the enzyme's activity. Highly refined structures have been deduced for the complexes between trypanosomal triosephosphate isomerase and a substrate analogue (glycerol-3-phosphate to 2.2 Å), a transition state analogue (3-phosphonopropionic acid to 2.6 Å), and a compound structurally related to both (3-phosphoglycerate to 2.2 Å). The active site structures of these complexes were compared with each other, and with two previously determined structures of triosephosphate isomerase either free from inhibitor or complexed with sulfate. The comparison reveals three conformations available to the “flexible loop” near the active site of triosephosphate isomerase: open (no ligand), almost closed (sulfate), and fully closed (phosphate/phosphonate complexes). Also seen to be sensitive to the nature of the active site ligand is the catalytic residue Glu-167. The side chain of this residue occupies one of two discrete conformations in each of the structures so far observed. A “swung out” conformation unsuitable for catalysis is observed when sulfate, 3-phosphoglycerate, or no ligand is bound, while a “swung in” conformation ideal for catalysis is observed in the complexes with glycerol-3-phosphate or 3-phosphonopropionate. The water structure of the active site is different in all five structures. The results are discussed with respect to the triosephosphate isomerase structure function relationship, and with respect to an on-going drug design project aimed at the selective inhibition of glycolytic enzymes of T. brucei.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100106
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  • 4
    Electronic Resource
    Electronic Resource
    Reverse micelles in protein separation: The use of silica for the back-transfer process (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 41 (1993), S. 489-492 
    Details
    ISSN: 0006-3592
    Keywords: reverse micelles ; back-extraction ; silica ; proteins ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In order to use reverse micellar solutions successfully for the separation of proteins, good methods are needed to recover the biomolecules into an aqueous environment after solubilization into organic micellar media. Usually the recovery is accomplished by equilibrating the protein-loaded reverse micellar solution with a water phase containing an appropriate salt (back-transfer). In this article we describe an alternative “back extraction” procedure which is based on the addition of silica to the protein-containing reverse micellar solution. In this way, the water is stripped from the reverse micellar solution. [i.e., bis(2-ethylhexyl) sodium sulfosuccinate (AOT)/isooctane/water] and the proteins adsorb to the silica particles. The adsorption process is shown to be practically quantitative. The subsequent recovery of the proteins form the silica into an aqueous solution turns out to be most efficient at alkaline pH (pH 8); 60-80 of the total protein (α-chymotrypsin or trypsin) could be recovered. The specific enzyme activity at the end of the whole cycle can be as high as 80-100%. The procedure is applied also for the back extraction from micellar solutions in which, instead of AOT, a biocompatible surfactant such as a synthetic short-chain lecithin was used. It is shown that the recovery of a α-chymotrypsin and trypsin is also achievable under these conditions in quite good yield and under good maintenance of the enzyme's catalytic activity. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260410413
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  • 5
    Electronic Resource
    Electronic Resource
    Characterization of thermal diffusion of copolymers in solution by thermal field-flow fractionation (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 2673-2680 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Extending our earlier measurements of homopolymer thermal diffusion, we characterize here the thermal diffusion of nine copolymers in toluene by thermal field-flow fractionation (thermal FFF). The copolymers are organized into groups whose members differ in one major aspect only. These differences include monomer ratios in random copolymers, block arrangements in block copolymer pairs having both linear and star-shaped configurations, and arm numbers and arm molecular weights in star-shaped copolymers. By examining the influence (or lack thereof) of these distinctive features on the thermal diffusion coefficient DT, the general phenomenon of thermal diffusion in polymer solutions is further characterized. Specifically, two principal observations are made. First, for copolymers subject to the radial segregation of its monomers, thermal diffusion appears to be dominated by the monomers preferentially located in the outer (free-draining) region of the solvated polymer molecule. Second, for copolymers lacking monomer segregation, DT can be described by a weighted average of the DT values of the corresponding homopolymers, where the weighting factors are the mole-fractions of each monomer type in the copolymer.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1990.090281313
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  • 6
    Electronic Resource
    Electronic Resource
    Human prostate cancer model: Roles of growth factors and extracellular matrices (1992)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 50 (1992), S. 99-105 
    Details
    ISSN: 0730-2312
    Keywords: extracellular matrices (ECMs) ; bFGF ; NGF ; HGF and KGF ; growth factors (GFs) ; human prostate cancer model ; prostate cancer-bone interaction ; stromal-epithelial interaction ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: A human prostate cancer model was established by inoculating a prostate specific antigen (PSA)-producing LNCaP cell line with either prostate or bone fibroblasts. Alternatively, this human prostate cancer model can also be established by inoculating LNCaP cell with growth factor(s) (GFs) and extracellular matrix (ECM) immobilized on Gelfoam®. The resulting LNCaP tumors were used to evaluate PSA production and excretion athymic hosts. This model was also employed to examine the biochemical nature of mesenchymal cell-derived growth-promoting protein(s) and to assess the efficacy of potential chemotherapeutic agents. Because of the propensity of human prostate cancer to metastasize to the bone, this study defined a 1.0 M NaCI-eluted fraction, MS1, from the conditioned medium of a bone stromal cell line (MS) by heparin-affinity column chromatography. The growth-promoting activity was assayed both in vivo (e.g., tumor formation) and in vitro (e.g., soft agar colony formation). We found that the growth-promoting activity was trypsin-and heat-sensitive, and partially degraded by acid and dithiothreitol. Immunochemical studies indicated that the polyclonal antibody raised against MS1 blocked the growth-promoting effect elicited by the bone-conditioned media. This growth-promoting factor was found to be immunochemically dissimilar to KGF, HGF, and bFGF. However, addition of bFGF, HGF and NGF, but not a FGF, TGFβ, IGF1, IGF2, PDGF, EGF, TGFα and KGF, stimulated anchorage-independent growth of prostate cells, a condition closely parallel to tumor formation in vivo. We found that the MS1 fraction also contained fibronectin and tenascin but not laminin or collagen IV. None of the ECM proteins induced soft agar colony formation by normal prostate epithelial cells. Therefore, it is possible that the ECM protein(s) may potentiate the tumor-inducing activity of locally produced GFs. © 1992 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240501222
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  • 7
    Electronic Resource
    Electronic Resource
    C2-Symmetrical Pyrrolidine Derivatives Chiral Auxiliaries in Radical Chemistry (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 441-450 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fumaramides 3b and 3c bearing the C2-symmetrical pyrrolidine moieties (2R,5R)-2,5-bis(methoxymethyl)pyrrolidine (2b) or 1,3:4,6-di-O-benzylidene-2,5-dideoxy-2,5-imino-L-idit (2c), respectively, as a chiral auxiliary lead to high diastereoselectivities in radical reactions (‘tin method’;Scheme 1). Removal of the chiral auxiliaries affords the corresponding alkylated fumaric acids Scheme 2. Single-crystal X-ray structures of 3b and 3c support arguments that lead to the model of 1,4-stereoinduction.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760128
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  • 8
    Electronic Resource
    Electronic Resource
    Cycloaddition Reactions in Carbohydrate Chemistry. (Reihe: ACS Symposium Series, Vol. 494, Reihenherausgeber: M. J. Comstock, Herausgegeben von R. M. Giuliano. American Chemical Society, Washington DC, 1992. X, 181 S., geb. 49.95$. - ISBN 0-8412-2429-3 (1993)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 105 (1993), S. 1271-1272 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19931050849
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  • 9
    Electronic Resource
    Electronic Resource
    Preparation and crystal structure of the Isotypic Carbides Ln4Ni2C5 (Ln = Er, Tm, Yb and Lu)Dedicated to Professor Hartmut Bärnighausen on his 60th Birthday (1993)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 619 (1993), S. 321-326 
    Details
    ISSN: 0044-2313
    Keywords: Lanthanoid nickel carbides, Ln4Ni2C5 ; crystal structure ; magnetic susceptibility ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Darstellung und Kristallstruktur der isotypen Carbide Ln4Ni2C5 (Ln = Er, Tm, Yb und Lu)Die Titelverbindungen wurden durch Reaktion der Elemente in einer Lithiumschmelze hergestellt und ihre Kristallstruktur aus Einkristalldaten der Ytterbiumverbindung bestimmt. Sie kristallisieren rhombisch, Pmm2, a = 352,88(6) pm, b = 1 143,0(3) pm, c = 366,16(6) pm, Z = 1, R = 0,020 für 1 261 Strukturfaktoren und 29 variable Parameter. Die Struktur enthält eine Abfolge von Schichten, wie sie von CeNiC2 und ScC (NaCl Typ) bekannt sind. Dementsprechend enthält sie C2-Paare mit einem C—C-Abstand von 138(1) pm und isolierte Kohlenstoffatome. Zusammen mit den Nickelatomen bilden die C2-Paare eindimensional-unendliche Verbände der Zusammensetzung [Ni2C4]n. Das fünfte Kohlenstoffatom ist oktaedrisch von Ytterbiumatomen umgeben. Daher kann die Verbindung mit (formalen) Oxidationszahlen gemäß der Formel (Yb3+)4[Ni2C48-]C4- beschrieben werden. Die magnetischen Suszeptibilitäten von Yb4Ni2C5 zeigen Curie-Weiss-Verhalten mit einem magnetischen Moment von μexp = 4,44 μB in guter Übereinstimmung mit dem für Yb3+ zu erwartenden Wert von μeff = 4,53 μB.
    Notes: The title compounds were prepared from the elemental components in a lithium flux. Their crystal structure was determined for the ytterbium compound from single-crystal X-ray data. It is orthorhombic, Pmm2, a = 352.88(6) pm, b = 1 143.0(3) pm, c = 366.16(6) pm, Z = 1, R = 0.020 for 1 261 structure factors and 29 variable parameters. The structure may be viewed as an intergrowth of slabs consisting of the CeNiC2 and the ScC (NaCl type) structures. It thus contains C2 pairs with a C—C distance of 138(1) pm and isolated carbon atoms. Together with the nickel atoms the C2 pairs form one-dimensionally infinite building elements [Ni2C4]n. The fifth carbon atom is octahedrally coordinated by ytterbium atoms. Accordingly the compound may be rationalized to a first approximation with the formula (Yb3+)4[Ni2C48-]C4-. Yb4Ni2C5 shows Curie-Weiss behaviour with a magnetic moment of μexp = 4.44 μB per ytterbium atom in good agreement with the theoretical moment of μeff = 4.53 μB for Yb3+.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19936190216
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  • 10
    Electronic Resource
    Electronic Resource
    Theory and numerical modeling of x-ray fluorescence from multi-layer spheres (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 20 (1991), S. 245-254 
    Details
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A mathematical model has been developed for the quantitative x-ray fluorescence spectrometry of small spherical samples, e.g. targets containing diagnostic materials for inertial confinement fusion experiments. The model corrects for matrix effects in a multi-layer spherical geometry much as existing programs now do for thin films or bulk samples. Attenuation effects have been found to be greater in a shell geometry than in a comparable thin-film geometry because multiple passes through the shell are possible and because many paths in or out are nearly tangential to the shell. In both cases the path is longer and attenuation is greater. The model for primary fluorescence from uniform shells has also been extended to approximate the fluorescence from non-uniform shells. This allows one to predict how experimental results would vary with sample mounting if excess material were oriented toward or away from the x-ray beam or the detector or away from both. Finally, a simplified model for estimating the magnitude of secondary fluorescence effects is presented.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/xrs.1300200506
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