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Glyoxylate for affinity labelling of 6-phosphogluconate dehydrogenase
No full textIn order to find a new reagent for the affinity labelling, 6-phosphogluconate dehydrogenase was treated with glyoxylate, a versatile metabolite with a carboxyl and a reactive aldehydic group. High concentrations of glyoxylate inhibit the enzyme, while in the presence of the reducing agent cyanoborohydride, the enzyme is irreversibly inactivated by only millimolar glyoxylate. This indicates the formation of a Schiff base between the aldehydic group of glyoxylate and one enzyme lysine residue. The kinetics and substrate competition suggest that inactivation is due to affinity labelling. In the first step the inhibitor carboxylic group binds to the substrate carboxyl binding site, and in the second slower step the aldehydic group binds a nearby lysine. We have also found that other enzymes are inactivated by the combined actions of glyoxylate and cyanoborohydride, with a saturation kinetics. Hence, glyoxylate can be helpful to identify specific lysines at the carboxyl binding sites in pro..
Inhibitors behaviour agree with the 3-dimensional structure of the active site in 6-phosphogluconate dehydrogenases
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Bromopyruvate for the affinity labelling of a single cysteine residue near the carboxylate binding site of lamb liver 6-phosphogluconate dehydrogenase
No full textBromopyruvate inactivates 6-phosphogluconate dehydrogenase by affinity labeling. Kinetic analyses, stoichiometry and isolation of a single labelled tryptic peptide of the modified protein indicate that inactivation is due to the affinity labeling of a single cysteine residue, identified as cysteine 401. It thus appears that this cysteine is within a short distance from the protein site involved in the binding of the carboxylate group of the substrate. These results suggest that the carboxylate binding site of proteins could be used as an anchorage point for affinity labeling, and that bromopyruvate can be used to individuate an amino acid residue within few Å from this site
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
Breaking a multistep reaction
No full textThe K185H mutant of T. brucei 6PGDH is able to catalyse the redox step but not decarboxylation
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