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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    European biophysics journal 13 (1986), S. 291-299 
    ISSN: 1432-1017
    Schlagwort(e): Hexokinase (wheat germ) ; conformational change, hysteresis ; pulse fluorimetry ; synchrotron radiation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract The conformational properties of wheat germ hexokinase LI, a monomeric enzyme showing non-Michaelian kinetics, have been studied by polarised pulse fluorimetry using synchrotron radiation as an excitation light source. The fluorescence decays and the fluorescence anisotropy decays of tryptophyl residues were measured with excitation at 300 nm. At pH 8.5, we found that the “mnemonical” temperature-dependent transition did not induce any detectable structural change in the protein. This rules out modifications of the aggregation state of hexokinase during the transition as well as important conformational changes in the tertiary structure. At pH 6.1, a temperature-dependent transition of the enzyme-glucose binary complex is observed: rapid, large amplitude, internal motions appear in the structure when the temperature is raised from-1°C to 30°C. Full standard activity is retained during this dynamic change. In the experiments described here we obtained an active fluorescent derivative by reacting hexokinase with N-(iodoacetylaminoethyl)-5-naphtylamine-1-sulfonic acid (1,5-IAEDANS), in the presence of glucose. Polarised fluorescence decay measurements indicate that the label is exposed to the solvent and very mobile, which makes it ineffective as a probe for the conformational properties of hexokinase.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 12
    ISSN: 1573-4994
    Schlagwort(e): Lifetime distributions ; heterogeneities ; associated dynamics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract After purification to homogeneity by Bio-Rex 70 ion exchange chromatography, micromolar solutions ofNaja nigricollis cardiotoxin were found to contain significant amounts of aggregates, as detected by time-resolved polarized fluorescence of its single tryptophan residue. The level of cardiotoxin aggregation depends strongly and reversibly on the protein concentration and pH. However, supplementary reverse-phase HPLC completely suppresses this aggregation, resulting in all cases in fluorescence anisotropy decays characteristic of the pure cardiotoxin monomer. The self-association properties of cardiotoxin, in the presence of a possible cofactor eliminated by the HPLC step, may be functionally relevant, and would deserve further investigation. The physical heterogeneity of the cardiotoxin samples required an appropriate model for the analysis of fluorescence depolarization, which was iteratively improved by comparison with experimental results. In this way, an approximate molar fraction of 10–15% aggregated cardiotoxin at a 90ΜM total protein concentration, pH 7, was determined. The fluorescence of the partly aggregated samples is significantly perturbed as compared to the HPLC-treated monomer, indicating that the cardiotoxin aggregate must have an increased average fluorescence lifetime and a strongly decreased initial anisotropy. The decrease in initial anisotropy suggests either an increased mobility of the tryptophan residue upon aggregation or fast energy transfers between residues of different cardiotoxin molecules brought within a short distance in the aggregate. This study illustrates the high sensitivity of the time-resolved fluorescence technique, through both total fluorescence and anisotropy parameters, to low levels of physical or chemical heterogeneity in a protein sample.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Journal of fluorescence 5 (1995), S. 193-194 
    ISSN: 1573-4994
    Schlagwort(e): Maximum entropy method ; frequency-domain fluorometry ; lifetime distributions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The new quantified version of the maximum entropy method allows one to recover lifetime distributions with a precise statement of the accuracy of position, surface, and broadness of peaks in the distribution. Applications to real data (2,6-ANS in aqueous solutions of sodium dodecyl sulfate micelles of Β-cyclodextrin) are presented.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 14
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The absorption, CD, and fluorescence emission spectra, and the fluorescence emission and depolarization lifetimes of the human granulocyte-macrophage colony-stimulating factor (hGM-CSF) and related peptides previously tested for their immunological activity, were measured in water at various pHs and temperatures to obtain information on their conformation in solution. The aim was to correlate the amino acid sequences, and the chain conformations and dynamics of the peptides, with their immunological propertiesThe CD spectrum of hGM-CSF revealed, as expected, a structure in solution similar to that in the crystalline state, but the fluorescence data suggest that the Trp 122 residue is more accessible to the solvent than the x-ray data would lead one to expect. They also suggest that some flexibility exists between the protein's two domains, one made up of theα-helices A and C and the other of the α-helices B and D plus the two β-strands. In aqueous solution, none of the tested peptide CD spectra could be linked to a recognizable ordered conformation, i.e., an α-helix or a β-sheet. The fluorescence of the peptide 11-24 suggests that the Trp 13 residue may appear in two types of situations: (a) in aqueous solution and (b) within a globular structure. Its CD spectra show that the tryptophan residue exists in both cases in a highly asymmetric environment independent of the pH. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 15
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 20 (1981), S. 41-48 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synchrotron radiation has been used to determine the fluorescence decay parameters of a tryptophan-containing oligopeptide, Lys-Trp-Lys, bound to nucleic acids. All fluorescence decay curves can be fitted by a sum of two exponentials. The two lifetimes very likely correspond to two conformational states of the oligopeptide. The mean fluorescence lifetime of the peptide is not markedly affected upon binding to nucleic acids even though the fluorescence quantum yield is strongly reduced. A model is presented that accounts for the existing fluorescence data: two consecutive complexes are formed both involving electrostatic interactions. In one of the complexes the tryptophyl ring is stacked with the nucleic acid bases and its fluorescence is completely quenched. The other complex emits a fluorescence having characteristics which are similar to those of the free peptide.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 16
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The micellization and the interactions with lipid vesicles of the antifungal cyclic lipopeptide iturin A have been investigated by nanosecond pulse fluorometry of a D-tyrosyl residue. We show that this lipopeptide has three conformers in solution whose proportions are modified during the micellization process. Below the critical micellar concentration (CMC) iturin A does not self-associate inside the bilayer. Above the CMC all the molecules of iturin A interact with the vesicles and self-associate inside the membrane.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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