1,721,005 research outputs found
Theoretical study of the electronic states of the Rb-2 molecule
No full textWe have calculated the electronic states of Rb-2 by multireference configuration interactions using the averaged relativistic effective small-core potential and the core-polarization potential. The potential energy curves for a large number of states dissociating into from 5s + 5s up to 7s + 5s asymptotic limits are calculated and the spectroscopic constants are reported. The spin-orbit effects for the states dissociating into 5p + 5s and 4d + 5s are calculated using the effective spin-orbit potential. The results are compared with available experimental data and other theoretical works. (C) 2001 Academic Press
Proton NMR Studies of Subtilisin Carlsberg : Binding of Monovalent and Divalent Metal Ions
No full textCrystal structure of tRNA(m(1)G37)methyltransferase: insights into tRNA recognition
No full texttRNA(m(1)G37)methyltransferase (TrmD) catalyzes the transfer of a methyl group from S-adenosyl-l- methionine (AdoMet) to G(37) within a subset of bacterial tRNA species, which have a G residue at the 36th position. The modified guanosine is adjacent to and 3' of the anticodon and is essential for the maintenance of the correct reading frame during translation. Here we report four crystal structures of TrmD from Haemophilus influenzae, as binary complexes with either AdoMet or S-adenosyl-l-homocysteine (AdoHcy), as a ternary complex with AdoHcy and phosphate, and as an apo form. This first structure of TrmD indicates that it functions as a dimer. It also suggests the binding mode of G(36)G(37) in the active site of TrmD and the catalytic mechanism. The N-terminal domain has a trefoil knot, in which AdoMet or AdoHcy is bound in a novel, bent conformation. The C-terminal domain shows structural similarity to trp repressor. We propose a plausible model for the TrmD(2)-tRNA(2) complex, which provides insights into recognition of the general tRNA structure by TrmD.
Crystallization and preliminary X-ray crystallographic analysis of tRNA(m(1)G37)methyltransferase from Haemophilus influenzae
No full textThe enzyme tRNA(m(1)G37)methyltransferase (TrmD) catalyzes the transfer of a methyl group from S-adenosyl-L-methionine (AdoMet) specifically to guanosine at position 37 within a subset of tRNA species in bacteria. The modified guanosine is next to the anticodon and is important for the maintenance of the correct reading frame during translation. TrmD from Haemophilus influenzae with both Nand C-terminal tags was overexpressed in Escherichia coli and crystallized at 297 K using sodium acetate as a precipitant. Native X-ray diffraction data were collected to 1.85 Angstrom resolution. The crystals are rhombohedral, belonging to the space group R32, with unit-cell parameters a = b = 98.05, c = 176.79 Angstrom, alpha = beta = 90, gamma = 120degrees. The presence of one monomer of recombinant TrmD in the crystallographic asymmetric unit gives a V-M of 3.07 Angstrom(3) Da(-1) and a solvent content of 59.9%.
Crystal structure of peptide deformylase from Staphylococcus aureus in complex with actinonin, a naturally occurring antibacterial agent
No full textCrystal structure of carboxylesterase from Pseudomonas fluorescens, an alpha/beta hydrolase with broad substrate specificity
No full textBackground: A group of esterases, classified as carboxylesterases, hydrolyze carboxylic ester bonds with relatively broad substrate specificity and are useful for stereospecific synthesis and hydrolysis of esters. One such carboxylesterase from Pseudomonas fluorescens is a homodimeric enzyme, consisting of 218-residue subunits. It shows a limited sequence similarity to some members of the alpha/beta hydrolase superfamily. Although crystal structures of a number of serine esterases and lipases have been reported, structural information on carboxylesterases is very limited. This study was undertaken in order to provide such information and to understand a structural basis for the substrate specificity of this carboxylesterase. Results: In this study, the crystal structure of carboxylesterase from P. fluorescens has been determined by the isomorphous replacement method and refined to 1.8 Angstrom resolution. Each subunit consists of a central seven-stranded beta sheet flanked by six a helices, The structure reveals the catalytic triad as Ser114-His199-Asp168. The structure of the enzyme in complex with the inhibitor phenylmethylsulfonyl fluoride has also been determined and refined to 2.5 Angstrom, The inhibitor is covalently attached to Ser114 of both subunits, with the aromatic ring occupying a hydrophobic site defined by the aliphatic sidechains of Leu23, lle58, Ile70, Met73 and Val170. No large structural changes are observed between the free and inhibitor-bound structures. Conclusions: Carboxylesterase from P. fluorescens has the alpha/beta hydrolase fold and the Ser-His-Asp catalytic triad. The active-site cleft in each subunit is formed by the six loops covering the catalytic serine residue. Three of the active-site loops in each subunit are involved in a head-to-head subunit interaction to form a dimer; it may be these extra structural elements, not seen in other esterases, that account for the inability of carboxylesterase to hydrolyze long chain fatty acids. As a result of dimerization, the active-site clefts from the two subunits merge to form holes in the dimer. The active-site clefts are relatively open and thus the catalytic residues are exposed to the solvent. An oxyanion hole, formed by nitrogen atoms of Leu23 and Gln115, is present in both the free and inhibitor-bound structures. An open active site, as well as a large binding pocket for the acid part of substrate, in P. fluorescens carboxylesterase may contribute to its relatively broad substrate specificity
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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