1,720,979 research outputs found
Carter (Ronald) and Long (Michael N.). The Web of Words. Exploring Literature through Language
No full textD'Amelio N. Carter (Ronald) and Long (Michael N.). The Web of Words. Exploring Literature through Language. In: Revue belge de philologie et d'histoire, tome 70, fasc. 3, 1992. Langues et littératures modernes — Moderne taal- en letterkunde. pp. 834-835
1H-NMR Studies of Copper Binding by Histidine Containing Peptides
No full textWe review recent developments in the studies of Cu(II) complexes with histidine-containing peptides in solution by NMR. An overview of the theoretical background of the effects of the paramagnetic metal on the NMR properties (relaxation and shift) of nearby nuclei is given. Particular attention is paid to the effect of exchange rates between free and metal-bound forms of the ligand on detection of paramagnetic relaxation rates. General methods are underlined to determine the structure of the complexes (and thus the donor set to the metal) and to distinguish between the binding of copper(II) to either N-1 or N-3 of the imidazole ring of histidine. Examples are reported dealing with fragments of the amyloid precursor protein (a protein related to Alzheimer's disease) and of the prion protein (related to Creutzfeldt–Jakob disease) in which the binding of copper may be relevant for subsequent redox activities, protein aggregation or metal-catalyzed protein damage
cis-trans Isomerization of β-casomorphin peptides bound to copper(II):: integration of EPR and NMR studies
No full textCopper complexes of beta -casomorphin peptides (BCM-7, BCM-5, BCM-4) were investigated by EPR and NMR in DMSO-d(6) solutions. Speciation of copper among many of the possible isomers was apparent. Computer simulations of low and room temperature EPR allowed the number of co-ordinated nitrogens in the major species (2 for BCM-4 and BCM-5, 4 for BCM-7) to be inferred and a rotational correlation time of 0.18 ns at 298 K to be evaluated for all complexes. All isomers of BCM-4 and BCM-5 were shown to bind copper, but the resulting structures were strictly determined by the conformational state of (2)Pro. The trans, rather than the cis, conformation was shown to allow binding of the deprotonated (3)Phe-NH; the terminal amino and carboxylate groups provided the other binding groups in all cases. Structures were obtained by constrained molecular dynamics using copper-proton distances obtained from paramagnetic nuclear relaxation rates. In the case of BCM-7, only the cis-cis-trans and/or the cis-cis-cis isomers were not binding copper. The conformational state of each Pro was shown to drive formation of the copper-nitrogen bond within the immediately adjacent residue, leading to the complex having four co-ordinated nitrogens in the case of the trans-trans-trans isomer
Calcium ions affect the exchange network but not the structure of a small peptide (melanostatin) in solution: a 1H- and 13C-NMR study
No full textThe interaction of calcium ions with the peptide hormone melanostatin (Pro-Leu-Gly-NH2) was investigated by H-1 and C-13 NMR spectroscopy in [D-6]DMSO containing H2O (1%). Chemical shifts, spin-lattice relaxation rates, H-1 NOESY maps and the temperature coefficients of the amide 1H NMR chemical shifts were measured at increasing concentrations of calcium. A 1:1 complex with the metal coordinated to the carbonyl moieties of Pro and Gly (K-d = 17 +/- 2 mM(-1)) was shown to be the major species in solution, although evidence was also provided for the occurrence of a minor species with the metal bound to the Leu carbonyl and with different stoichiometry. Upon metal complexation, substantial changes in the intrinsic chain flexibility of the peptide and in the exchange rates between water and amide protons were detected
Metal ion effects on cis/trans isomerization of proline residues in short chain peptides in solution
No full textThe-effect of capper(II) ions on the probabilities of existence of the four detectable conformers of the tetrapeptide Tyr-Pro-Phe-Pro (beta -casomorphin 4) in [H-2(6)]DMSO was investigated by H-1 NMR Spectroscopy. Integration of the Phe-NH signals provided the relative populations in the free state as tt/tc/ct/cc = 28.34.29:9 at 293 K (c = cis, t = trans). Copper(ii) was shown to bind to all four isomers, yielding complexes with two different structures, depending on the conformation of Pro(2). The interpretation of paramagnetic relaxation rates of Pro(2)-H alpha signals provided the corresponding isomeric probabilities in the metal-bound state as 13:36:20:31. The observed stabilization of the conformation with the lowest probability of-existence (cc) may be relevant for the biological role of copper and other metal ions
Solution structures of cyclosporin a and its complex with dysprosium(III) in SDS micelles: NMR and molecular dynamics studies
No full textCyclosporin A (CsA) is a cyclic naturally occurring peptide used to prevent graft rejection in organ transplantations. Its immunosuppressive activity is due to the formation of a complex with cyclophilin A (Cyp), in which the cis 9MeLeu−10MeLeu amide bond of CsA assumes a trans conformation. The mechanism of the conformational inversion has not been delineated, but it has been postulated that metal ions binding induces a conformational change that enables CsA to bind Cyp. In this work, we solved the structures of CsA in sodium dodecyl sulfate (SDS) micelles (which enhance its solubility and mimic the hydrophobic environment clinically used for drug delivery) and its complex with Dy(III) ion, whose coordination chemistry is frequently used to reproduce the effect of Ca(II). The paramagnetic properties of Dy(III) allowed us to build up a structure using proton relaxation enhancements, which remains stable in a MD simulation in the micelle environment
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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