1,720,962 research outputs found
Phenothiazines inhibit acetylcholinesterase by concentration-dependent-type kinetics. A study with trifluoperazine and perphenazine
No full textThe properties of perphenazine (PPZ) and trifluoperazine (TFP) as fluorescent dyes were exploited to calculate their critical micellar concentrations. The relative fluorescence quantum yield of the two amphiphiles was dependent on their concentration, abruptly decreasing above 30-40 muM PPZ and 20-30 muM TFP. Evidence is presented that this phenomenon is driven by the formation of nonfluorescent drug aggregates. The type of inhibition kinetics displayed by PPZ and TFP on human erythrocyte acetylcholinesterase (AChE) was also dependent on drug concentration, turning from noncompetitive to a "mixed" inhibition type at concentrations at which PPZ and TFP were demonstrated to undergo micelle formation. Results support the notion that phenothiazines may interact with AChE both as monomers and micellar aggregates, producing different inhibitory effects
A STUDY OF HUMAN ERYTHROCYTE ACETYLCHOLINESTERASE INHIBITION BY CHLORPROMAZINE
No full textMembrane-bound acetylcholinesterase (AChE) from the human erythrocyte is inhibited by chlorpromazine (CPZ) in a concentration range within which this amphiphilic drug has been demonstrated to interact with erythrocyte membranes, causing a large spectrum of physical and structural effects; membrane solubilization with 0.5% Triton X-100 results in a complete loss of CPZ inhibitory potency. Although these observations might suggest a role for membrane lipid environment in mediating human erythrocyte AChE inhibition, we observed that CPZ retains its full inhibitory effect on the fraction of enzyme (5-6% of total) that is solubilized from erythrocytes upon treatment with phosphatidylinositol-specific phospholipase C (PI-PLC) from Bacillus thuringiensis; furthermore, Triton X-100 is able to reverse the CPZ effect also in the case of PI-PLC-solubilized enzyme. These results demonstrate unequivocally that CPZ inhibits human erythrocyte AChE through direct molecular interaction. The inhibition kinetics displayed by CPZ on human erythrocyte AChE are dependent on drug concentration: evidence is provided that this phenomenon may be related to formation of CPZ micellar aggregates
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
Dispelling 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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