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A multiple role for the coenzyme in the mechanism of action of 6-phosphogluconate dehydrogenase
No full text6-Phosphogluconate dehydrogenase from Candida utilis
catalyzes the oxidative decarboxylation of 2-deoxy-6-phosphogluconate.
The 3-keto-2-deoxy-6-phosphogluconate, an
intermediate of the reaction, is reduced to 2-deoxy-6-phosphogluconate
and decarboxylated to I-deoxyribulose 5-phosphate
when incubated with the enzyme and TPNH. The
decarboxylation process does not occur in the absence of
the reduced coenzyme, which does not have, in this step,
an oxidation-reduction role.
Since TPNH also has a non-redox role in a tritium exchange
reaction catalyzed by the enzyme, it appears that the
coenzyme has a multiple role in the mechanism of action of
6-phosphogluconate dehydrogenase: a redox role in the dehydrogenation
and another (or others) role(s) in the decarboxylation
and tritium exchange reactions.
The hydroxyl group present at carbon 2 of 6-phosphogluconate
seems to have a dual role in the mechanism of
action of the enzyme: one in the binding of the substrate to
the enzyme, another in enhancing the decarboxylation of the
dehydrogenation product.
These findings are discussed with relations to the mechanism
of action of isocitrate dehydrogenase and of the malic
enzyme.
The enzymatic oxidative decarboxylation of 2-deoxy-6-
phosphogluconate is a new step for the metabolism of the
metabolic inhibitor 2-deoxyglucose
Differentiation between the structural and redox roles of TPNH in 6-phosphogluconate dehydrogenase
No full textIn the tritium exchange reaction catalysed by 6-phosphogluconate dehydrogenase from Candida utilis, the natural reduced coenzyme, 1-4 TPNH, has been substituted efficiently by its non enzymatically oxidizable isomer, 1-4 TPNH. This indicates that, in the tritium exchange reaction, the TPNH has not a redox but a structural role. We suggest that, as for 6-phosphogluconate dehydrogenase, isomers of the natural coenzymes may be used to differentiate, and study separately, the redox and structural roles of pyridine coenzymes in dehydrogenases. © 1972.In the tritium exchange reaction catalysed by 6-phosphogluconate dehydrogenase from Candida utilis, the natural reduced coenzyme, 1-4 TPNH, has been substituted efficiently by its non enzymatically oxidizable isomer, 1-4 TPNH. This indicates that, in the tritium exchange reaction, the TPNH has not a redox but a structural role. We suggest that, as for 6-phosphogluconate dehydrogenase, isomers of the natural coenzymes may be used to differentiate, and study separately, the redox and structural roles of pyridine coenzymes in dehydrogenases. © 1972
Evidence for the proximity of a cysteinyl and a tyrosyl residue in the active sita of 6-phosphogluconate dehydrogenase
No full textThe treatement of 6-phosphogluconate dehydrogenase from Candida utilis with Dansyl chloride causes the modification of one amino acid residue per enzyme subunit and the inactivation of the enzyme. Either a cysteine or a tyrosine residuecan be modified, depending on the pH of the reaction mixture. The dansyl residue can be transferred fron one residue to the other suggesting that the vtwo amino acid residues are close in the tridimensional structure of the active site of the enzym
Evidences for the proximity of two sulfhydryl groups in the active site of 6-phosphogluconate dehydrogenase
No full textThe reaction between 6-phosphogluconate dehydrogenase from Candida Utilis and 5,5' dithiobis(2-nitrobenzoate) results in the inactivation of the enzyme. At pH 6.0 the inactivation can be correlated with the modification of only one SH group per enzyme subunit. The modified SH group can react with another SH group forming and intramolecular disulfide bridge. The results obtained suggest that the SH group of two cysteine residues are located close in the tridimensional structure of the enzym
Photocleavage of lamb liver phosphogluconate dehydrogenase by vanadate supports an alternative subunits kinetic model
No full textIdentification of the chemical groups involved in the binding of periodate-oxidized NADP+ to 6-phosphogluconate dehydrogenase.
No full textPeriodate-oxidized NADP+ binds specifically and reversibly to the NADP+ binding site of 6-phosphogluconate dehydrogenase (EC 1.1.1.44) from Candida utilis. The inhibition can be stabilized by reduction with sodium borohydride. It has been shown that an aldehydic group of the inhibitor forms a Schiff base with a lysine residue of the enzyme
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
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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