1,721,006 research outputs found
Preliminary X-ray Crystallographic Analysis of a Highly Thermostable Phytase from Bacillus amyloliquefacience
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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
Calcium-dependent catalytic activity of a novel phytase from Bacillus amyloliquefaciens DS11
No full textThe thermostable phytase from Bacillus amyloliquefaciens DS11 hydrolyzes phytate (myoinositol hexakisphosphate, IP6) to less phosphorylated myo-inositol phosphates in the presence of Ca2+.. In this report, we discuss the unique Ca2+-dependent catalytic properties of the phytase and its specific substrate requirement. Initial rate kinetic studies of the phytase indicate that the enzyme activity follows a rapid equilibrium ordered mechanism in which binding of Ca2+ to the active site is necessary for the essential activation of the enzyme. Ca2+ turned out to be also required for the substrate because the phytase is only able to hydrolyze the calcium-phytate complex. In fact, both an excess amount of free Ca2+ and an excess of free phytate, which is not complexed with each other. can act as competitive inhibitors. The Ca2+-dependent catalytic activity of the enzyme was further confirmed, and the critical amino acid residues for the binding of Ca2+ and substrate were identified by site-specific mutagenesis studies. Isothermal titration calorimetry (ITC) was used to understand if the decreased enzymatic activity was related to poor Ca2+ binding. The pH dependence of the V-max and V-max/K-m consistently supported these observations by demonstrating that the enzyme activity is dependent on the ionization of amino acid residues that are important for the binding of Ca2+ and the substrate. The Ca2+-dependent activation of enzyme and substrate was found to be different from other histidine acid phytases that hydrolyze metal-free phytate
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
Asp-99 donates a hydrogen bond not to tyr-14 but to the steroid directly in the catalytic mechanism of Delta(5)-3-ketosteroid isomerase from Pseudomonas putida biotype B
No full textDelta(5)-3-ketosteroid isomerase (KSI) catalyzes the allylic isomerization of Delta(5)-3-ketosteroids at a rate approaching the diffusion Limit by an intramolecular transfer of a proton. Despite the extensive studies on the catalytic mechanism, it still remains controversial whether the catalytic residue Asp-99 donates a hydrogen bond to the steroid or to Tyr-14. To clarify the role of Asp-99 in the catalysis, two single mutants of D99E and D99L and three double mutants of Y14F/D99E, Y14F/D99N, and Y14F/D99L have been prepared by site-directed mutagenesis, The D99E mutant whose side chain at position 99 is longer by an additional methylene group exhibits nearly the same k(cat) as the wild-type while the D99L mutant exhibits ca. 125-fold lower k(cat) than that of the wild-type. The mutations made at positions 14 and 99 exert synergistic or partially additive effect on k(cat) in the double mutants, which is inconsistent with the mechanism based on the hydrogen-bonded catalytic diad, Asp-99 COOH...Tyr-14 OH ... C3-O of the steroid. The crystal structure of D99E/D38N complexed with equilenin, an intermediate analogue, at 1.9 Angstrom resolution reveals that the distance between Tyr-14 O eta and Glu-99 O epsilon is Ca. 4.2 Angstrom, which is beyond the range for a hydrogen bond, and that the distance between Glu-99 O epsilon and C3-O of the steroid is maintained to be ca, 2.4 Angstrom, short enough for a hydrogen bond to be formed. Taken together, these results strongly support the idea that Asp-99 contributes to the catalysis by donating a hydrogen bond directly to the intermediate
Crystal Structure of RNA Helicase from Genotype 1B Hepatitis C Virus: A Feasible Mechanism of Unwinding Duplex RNA
No full textAppropriate 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
A Low-Barrier Hydrogen Bond Playing an Important Role in the Enzyme Mechanism of delta-5-3-Ketosteroid Isomerase
No full textDispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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