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  • 1995-1999  (64)
  • 1985-1989  (17)
  • 1
    Call number: IASS 15.89494
    Type of Medium: Monograph available for loan
    Pages: Losebl.-Ausg.
    Edition: Stand: Oktober 2010
    ISBN: 9783768501828
    Language: German
    Branch Library: IASS Library
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  • 2
    ISSN: 1432-1017
    Keywords: Key words Vicinal coupling constants ; Polypeptide φ angles ; Karplus parameters ; Least-squares optimization ; Back-calculation of coupling constants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Quantitative φ-dihedral angle determinations of non-glycine and non-proline residues in Desulfovibrio vulgaris flavodoxin are carried out on the exclusive basis of 3 J coupling constants. In total 124 3 JHNH α , 123 3 JHNC ′i , 118 3 JHNC β , 117 3 JC′ i–1Hα , 109 3 JC′ i–1C′i , and 103 3 JC′ i–1Hβ values form the experimental basis for translating J coupling data into geometry information using various combinations of Karplus parameters given in the literature. In addition, each backbone torsional angle φ is adjusted assuming different models of local geometry, either a rigid torsion, a Gaussian distribution centered at a distinct angle, or a two-site jump model. Numerical optimization is followed by a statistical significance evaluation to assess the results. It is found that experimental coupling constants of most of the residues involved in secondary structure elements agree best with those predicted from rigid local conformations. For dihedral angles in loop regions, mobility effects are not negligible, and a single torsion (Glu 42) is likely to adopt two distinct adjustments. However, α-helix conformations with –60° 〈 φ 〈 –45° give rise to an alternate solution with φ≈+170° with similar statistical significance when using the four traditionally determined proton-involved 3 J couplings. This ambiguity is efficiently avoided only when taking advantage of the complete data set comprising six available experimental 3 J coupling constants and of the degeneracy intrinsic to the Karplus relation. The optimized φ conformations are compared with reference values from the crystal structure of flavodoxin.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 45 (1998), S. 0 
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In vivo, epimastigotes of Trypanosoma cruzi colonize a lipidic superficial layer of the rectal cuticle of the vector Triatoma infestans. In vitro, epimastigotes of four cultured strains and one strain from reduviids use a terminal area of the flagellum to attach to a variety of artificial hydrophobic substances, such as hydrocarbons and a range of synthetic plastics. Trypomastigotes did not attach to these substrates. Hydrophilic molecules, such as neutral or negatively charged polysaccharides. did not facilitate binding. Epimastigotes and trypomastigotes were artificially bound by electrostatic forces to positively charged chitosan or DEAE-Sephacel over their entire surface. Tween 20 and lipid-binding serum albumin effectively inhibited the hydrophobic attachment. Based on this hydrophobic interaction of epimastigotes. a new chromatography technique has been devised to gently separate trypomastigotes from epimastigotes using octacosane-coated beads. Furthermore, the in vitro transformation of epimastigotes to trypomastigotes was enhanced if epimastigotes were permitted to attach to hydrophobic, wax-coated culture vessels.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The repertoire of secondary metabolism (involving the production of compounds not essential for growth) in the plant kingdom is enormous, but the genetic and functional basis for this diversity is hard to analyse as many of the biosynthetic enzymes are unknown. We have now identified a key ...
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  • 5
    ISSN: 1432-2048
    Keywords: Key words: Conifers (Abies ; Picea ; Pinus ; Pseudotsuga) ; Ectomycorrhiza ; Phenylpropanoids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Tissue-specific accumulation of phenylpropanoids was studied in mycorrhizas of the conifers, silver fir (Abies alba Mill.), Norway spruce [Picea abies (L.) Karst.], white pine (Pinus strobus L.), Scots pine (Pinus silvestris L.), and Douglas fir [Pseudotsuga menziesii (Mirbel) Franco], using high-performance liquid chromatography and histochemical methods. The compounds identified were soluble flavanols (catechin and epicatechin), proanthocyanidins (mainly dimeric catechins and/or epicatechins), stilbene glucosides (astringin and isorhapontin), one dihydroflavonol glucoside (taxifolin 3′-O-glucopyranoside), and a hydroxycinnamate derivative (unknown ferulate conjugate). In addition, a cell wall-bound hydroxycinnamate (ferulate) and a hydroxybenzaldehyde (vanillin) were analysed. Colonisation of the root by the fungal symbiont correlated with the distribution pattern of the above phenylpropanoids in mycorrhizas suggesting that these compounds play an essential role in restricting fungal growth. The levels of flavanols and cell wall-bound ferulate within the cortex were high in the apical part and decreased to the proximal side of the mycorrhizas. In both Douglas fir and silver fir, which allowed separation of inner and outer parts of the cortical tissues, a characteristic transversal distribution of these compounds was found: high levels in the inner non-colonised part of the cortex and low levels in the outer part where the Hartig net is formed. Restriction of fungal growth to the outer cortex may also be achieved by characteristic cell wall thickening of the inner cortex which exhibited flavanolic wall infusions in Douglas fir mycorrhizas. Long and short roots of conifers from natural stands showed similar distribution patterns of phenylpropanoids and cell wall thickening compared to the respective mycorrhizas. These results are discussed with respect to co-evolutionary adaptation of both symbiotic partners regarding root structure (anatomy) and root chemistry.
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  • 6
    ISSN: 1432-2048
    Keywords: Key words: Arbuscular mycorrhiza ; Blumenol derivative ; Cyclohexenone derivative ; Glomus ; Nicotiana ; Isoprenoid induction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Tobacco (Nicotiana tabacum L.) plants were grown with and without the arbuscular mycorrhizal fungus, Glomus intraradices Schenk & Smith. High-performance liquid chromatographic analyses of methanolic extracts from mycorrhizal and non-mycorrhizal tobacco roots revealed marked fungus-induced changes in the patterns of UV-detectable products. The UV spectra of these products, obtained from an HPLC photodiode array detector, indicated the presence of several blumenol derivatives. The most predominant compound among these derivatives was spectroscopically identified as 13-hydroxyblumenol C 9-O-gentiobioside (“nicoblumin”), i.e. the 9-O-(6′-O-β-glucopyranosyl)-β-glucopyranoside of 13-hydroxy-6-(3-hydroxybutyl)-1,1,5-trimethyl-4-cyclohexen-3-one, a new natural product. This is the first report on the identification of blumenol derivatives in mycorrhizal roots of a non-gramineous plant.
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  • 7
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
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  • 8
    ISSN: 1573-5001
    Keywords: Vicinal coupling constants ; φ Torsion angle ; Karplus parametrization ; Desulfovibrio vulgaris flavodoxin ; Isotopic labelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract A triple-resonance NMR technique suitable for the determination ofcarbonyl-related couplings in polypeptide systems is introduced. Theapplication of three novel pulse sequences to uniformly13C/15N-enriched proteins yields E.COSY-likemultiplet patterns exhibiting either one of the3J(C′i−1,Hi α), 3J(C′i−1,Ci β) and3J(C′i−1,C′i)coupling constants in the indirectly detected 13C′dimension, depending on the passive spin selected. The experiments aredemonstrated with oxidized flavodoxin from Desulfovibrio vulgaris. On thebasis of the J-values measured and the backbone φ-angles derived from ahigh-resolution X-ray structure of the protein, the three associated Karplusequations were reparametrized. The root-mean-square differences between theexperimental coupling constants and those predicted by the optimized Karpluscurves are 0.41, 0.33 and 0.32 Hz for3J(C′i−1,Hi α),3J(C′i−1,Ci β) and3J(C′i−1,C′i),respectively. The results are compared with the Karplus parameters previouslypublished for the same couplings.
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  • 9
    ISSN: 1573-5001
    Keywords: Multiplet simulation ; Least-squares optimization ; Spectrum fitting ; Long-range couplings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A simple constant-time 3D heteronuclear NMR pulse sequence has been developed to quantitatively determine the heteronuclear three-bond couplings 3J(HN,C′) and 3J(Hβ,C′) in uniformly 13C-enriched proteins. The protocols for measuring accurate coupling constants are based on 1H,13C-heteronuclear relayed E.COSY [Schmidt, J.M., Ernst, R.R., Aimoto, S. and Kainosho, M. (1995) J. Biomol. NMR, 6, 95–105] in combination with numerical least-squares spectrum evaluation. Accurate coupling constants are extracted from 2D spectrum projections using 2D multiplet simulation. Confidence intervals for the obtained three-bond coupling constants are calculated from F-statistics. The three-bond couplings are relevant to the determination of ϕ and X 1 dihedral-angle conformations in the amino acid backbone and side chain. The methods are demonstrated on the recombinant 13C, 15N-doubly enriched 147-amino acid protein Desulfovibrio vulgaris flavodoxin with bound flavin mononucleotide in its oxidized form. In total, 109 3J(HN,C′) and 100 3J(Hβ,C′) coupling constants are obtained from a single spectrum.
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  • 10
    ISSN: 1573-5001
    Keywords: 2D heteronuclear NMR ; Isotope labeling ; Coupling constants ; Antamanide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A simple heteronuclear relayed E.COSY pulse sequence with a minimum number of pulses is proposed for the quantitative determination of heteronuclear three-bond J-coupling constants in uniformly 13C-enriched polypeptide samples. Numerous heteronuclear three-bond coupling constants, including $${}^3{\text{J}}_{{\text{H}}^{\text{N}} {\text{C}}'} $$ , $${}^3{\text{J}}_{{\text{H}}^{\text{N}} {\text{C}}^\beta } $$ , $${}^3{\text{J}}_{{\text{H}}^\beta {\text{C}}'} $$ , and $${}^3{\text{J}}_{{\text{H}}^\alpha {\text{C}}^\gamma } $$ , can be determined for each residue from a single heteronuclear relayed E.COSY spectrum. Couplings relevant for stereospecific assignments as well as for the determination of dihedral angles in the amino acid backbone and in side chains are obtained. The method is demonstrated on the uniformly 13C-enriched decapeptide antamanide (-Val1-Pro2-Pro3-Ala4-Phe5-Phe6-Pro7-Pro8-Phe9-Phe10-).
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