117,692 research outputs found
Introduzione
No full textIntroduzione alla riedizione anastatica degli emblemi delle regioni italiane dalla Iconologia di Cesare Ripa (sec. XVII)
Crystal-structure of the Ternary Complex Between Carboxypeptidase-a, L-phenylalanine, and the Azide Ion
No full textThe structure of the ternary complex of carboxypeptidase A (CPA) with the amino acid L-phenylalanine and the azide anion is reported as determined by X-ray crystallography to a resolution of 2.0 angstrom. The structure has been refined to an R factor of 0.151 over 7234 reflections having I > 2-sigma(I). The binding of the amino acid molecule to the enzyme hydrophobic pocket closely resembles that of D-phenylalanine with the carboxylate linked to Arg-145 and Asn-144 and its alpha-amino group linked to Glu-270. The azide anion binds to Arg-145, which is proposed as the high-affinity binding site for anions. Upon L-phe binding the Tyr-248 residue moves in the "down" position at contact distances with both the amino and the carboxylate groups of the bound amino acid. A region of electron density near the metal has been interpreted as a second azide ion directly coordinated to zinc as suggested by spectroscopic studies on cobalt-substituted CPA. The present structure confirms the proposed mechanism of CPA sensitivity toward anions
Dynamic properties of bovine Cu,Zn superoxide dismutase from crystallographic data
No full textThe Cu,Zn superoxide dismutase (SOD) enzyme from bovine erythrocytes has been the subject of several crystallographic studies over the last fifteen years. Nine crystal structures in space groups C2, P2(1)2(1)2(1) and C222(1), have been refined at high resolution and are available from the Protein Data Bank and our laboratory. We have performed a comparative analysis based on the experimentally determined structural variability in order to study the dynamics of the enzyme in terms of molecular flexibility. We have been able to show that information on molecular motions of different types occurring on different timescales may be obtained from the data by comparing thermal motion analysis with that of backbone C alpha fluctuations. We have found that the most mobile parts of Cu,Zn SOD are located in turns and loops and that there is a strict correlation between thermal motion and flexibility of the molecule, with the only exception of the two residues Asp11 and Glu38. The analysis of crystal polymorphism established the existence of a quite strict correlation between crystal contacts and mobility in space group C2, while in P2(1)2(1)2(1) and C222(1) the opposite was observed. Comparison with the results of molecular dynamics simulation revealed a good agreement between the two approaches although some differences emerge when active site residues are considered. The results of this work indicate the feasibility of an 'experimental' approach to the study of protein dynamics. (C) 1998 Elsevier Science S.A. All rights reserved
Brand Extensions: I contributi della letteratura di Industrial Organization
No full textModern companies adopt the brand extension strategies in order to maximize their brand equity, and the economists' interest about these practices has recently grown. The studies of Industrial Organization examine the relevant aspects of the brand extension: whether or not to extend, the timing of the extension, the markets involved, and the spillover effects. This paper discusses the main findings and the issues that need further research
Perché città e continenti hanno nomi di donna
No full textLa scienza retorica classica affidava alle donne (ma anche alle stanze, ai palazzi, alle figure architettoniche, agli armadi) la funzione simbolica di “contenere” informazioni e concetti. Sicché fu naturale per la geografia, scienza dei luoghi/loci, utilizzare, come avveniva negli emblemi, le figure femminili per indicare Città e Continenti (cioè appunto “quelli che contengono”)
Industrial wood wastes: experimental chemical-physical characterisation and non-controlled combustion tests
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