1,721,035 research outputs found
ACTIVE-SITE MUTATIONS OF THE DIPHTHERIA-TOXIN CATALYTIC DOMAIN - ROLE OF HISTIDINE-21 IN NICOTINAMIDE ADENINE-DINUCLEOTIDE BINDING AND ADP-RIBOSYLATION OF ELONGATION-FACTOR-2
No full textDiphtheria toxin (DT) has been studied as a model for understanding active-site structure and function in the ADP-ribosyltransferases. Earlier evidence suggested that histidine-21 of DT is important for the ADP-ribosylation of eukaryotic elongation factor 2 (EF-2). We have generated substitutions of this residue by cassette mutagenesis of a synthetic gene encoding the catalytic A fragment (DTA) of DT, and have characterized purified mutant forms of this domain. Changing histidine-21 to alanine, aspartic acid, leucine, glutamine, or arginine diminished ADP-ribosylation activity by 70-fold or greater. In contrast, asparagine proved to be a functionally conservative substitution, which reduced ADP-ribosylation activity by < 3-fold. The asparagine mutant was approximately 50-fold-attenuated in NAD glycohydrolase activity, however. Dissociation constants (Kd) for NAD binding, determined by quenching of the intrinsic protein fluorescence, were 15 microM for wild-type DTA, 160 microM for the asparagine mutant, and greater than 500 microM NAD for the alanine, leucine, glutamine, and arginine mutants. These and previous results support a model of the ADP-ribosylation of EF-2 in which histidine-21 serves primarily a hydrogen-bonding function. We propose that the pi-imidazole nitrogen of His-21 hydrogen-bonds to the nicotinamide carboxamide, orienting the N-glycosidic bond of NAD for attack by the incoming nucleophile in a direct displacement mechanism, and then stabilizing the transition-state intermediate of this reaction
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Streptococcus pneumoniae induces mast cell degranulation
No full textStreptococcus pneumoniae colonizes the nasopharynx of healthy human carriers, but occasionally can spread in the
body causing severe diseases. The mucosa of the respiratory tract is enriched in mast cells, key players of the innate
immune response. Here, we report on the interaction of various strains of S. pneumoniae with the mast cell line RBL-
2H3. Live, but not heat-killed. bacteria were found to induce mast cell degranulation in a dose- and time-dependent
manner, only partially controlled by cytosolic calcium, with no production of TNF-y and IL-6. Non-encapsulated
pncumococcal strains exhibited different potencies in triggering mast cells. We propose here that the induction of mast
cell dcgranulation by pneumococcal factors not accompanied by the production of pro-inflammatory cytokines may he
a specific strategy elaborated by this bacterium to promote its own spreading from the respiratory mucosa into the
environment
Unravelling the pathogenic role of Helicobacter pylori in peptic ulcer: Potential new therapies and vaccines
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Variations on the Author
Get PDF“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
Get PDFWe 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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