1,721,301 research outputs found
The application of triazine dyes in enzyme purification and structural studies
No full textA number of triazine dyes, including Cibacron blue F3G-A and Procion blue MX-R, have been covalently attached to microparticulate silica and used for the resolution of proteins by high performance liquid affinity chromatography (HPLAC). The versatility of HPLAC, a technique which combines the inherent speed and resolving power of high performance liquid chromatography (HPLC) with the biological specificity of affinity chromatography, was applied to the resolution of protein mixtures containing enzymes such as lactate dehydrogenase, hexokinase, alkaline phosphatase, carboxypeptidase G and L tryptophanyl-tRNA synthetase. In addition, the effect of divalent metal ions such as Mg + and Zn + on promoting the adsorption of enzymes to silica immobilised triazine dye adsorbents has been investigated. Dye-metal ionenzyme intractions are interpreted in terms of a structure-function relationship.The preparative scale purification of rabbit muscle lactate dehydrogenase from a crude extract was achieved on a HPLAC adsorbent comprising silica immobilised Procion blue MX-R. Bound enzyme was biospecifically eluted with NADH, to yield a homogeneous protein as judged by SDS polyacrylamide gel electrophoresis. Two further HPLAC adsorbents have been developed, silica immobilised acriflavin which functions as a charge transfer matrix and silica immobilised iminodiacetic acid which operates as a metal chelate affinity chromaiography adsorbent. The acriflavin-silica adsorbent is able to resolve mixtures of purines and pyrimidines, nucleosides and nucleotides, pyridine nucleotide coenzymes, flavins and aromatic amino acids, achieving separation in a fraction of the time required for similar separations by low-pressure liquid chromatography. The metal chelate HPLAC adsorbent was applied specifically to the purification -1f the metalloenzyme, carboxypeptidase G from a crude extract (10.8 u.mg ). Chromatography yielded a substantially purified enzyme (approx. 90%) as judged by-1SDS polyacrylamide gel electrophoresis with a specific activity of 248 u.mg. The ability of the dichlorotriazinyl dye, Procion blue MX-R, to mimic coenzyme binding was exploited as an affinity label for horse liver alcohol dehydrogenase. Chymotryptic digestion and resolution of peptides yielded a single dye modified peptide which was sequenced, and the site of labelling on the enzyme identified. The specific active-site directed reaction of Procion blue MX-R with horse liver alcohol dehydrogenase is interpreted in terms of the known crystallographic structure of the enzyme.</p
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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