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Redox thermodynamics of the ferric-ferrous couple of wild-type Synechocystis KatG and KatG(Y249F)
No full textCrystal structures and mass spectrometric analyses of catalase-peroxidases (KatGs) from different organisms revealed the existence of a peculiar distal Met-Tyr-Trp cross-link. The adduct appears to be important for the catalase but not the peroxidase activity of bifunctional KatG. To examine the effect of the adduct on enzyme redox properties and functions, we have determined the thermodynamics of ferric reduction for wild-type KatG and KatG(Y249F), whose tyrosine-to-phenylalanine mutation prevents cross-link formation. At 25 degrees C and pH 7.0, the reduction potential of wild-type KatG is found to be -226 +/- 10 mV, remarkably lower than the published literature values. The reduction potential of KatG(Y249F) is very similar (-222 +/- 10 mV), but variable temperature experiments revealed compensatory differences in reduction enthalpies and entropies. In both proteins, the oxidized state is enthalpically stabilized over the reduced state, but entropy is lost on reduction, which is in strong contrast to horseradish peroxidase, which also features a much more pronounced enthalpic stabilization of the ferriheme. With both proteins, the midpoint potential increased linearly with decreasing pH. We discuss whether the observed redox thermodynamics reflects the differences in structure and function between bifunctional KatG and monofunctional peroxidases
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
Impact of heme to protein linkages in peroxidases on redox chemistry and catalysis
No full textThe mammalian peroxidases participate in host defence against infection, hormone synthesis and pathogenesis. The most striking feature of these heme enzymes is the existence of two covalent ester bonds between the prosthetic group and the protein in the functional, mature proteins. Myeloperoxidase is unique in having an additional vinyl-sulfonium bond. The impact of heme distortion and asymmetry on the spectral and enzymatic properties is discussed as is the role of the MPO-typical electron withdrawing sulfonium ion linkage in raising the reduction potential of its redox intermediatesand maintaining a rigid solvent network at the distal heme cavity
Redox thermodynamics of the Fe3+/Fe2+ couple in wild type and mutated heme peroxidases
No full textThe thermodynamics of the one-electron reduction of the ferricheme in wild-type and mutated heme Synechocystis catalaseperoxidase and human myeloperoxidase were determined through spectro-electrochemical experiments. The data are interpreted in terms of ligand binding features, electrostatic effects and solvation properties of the heme environment
Bifunctional catalase-peroxidase is secreted by the rice blast fungus Magnaporthe grisea during oxidative burst
No full textRecently, it has been demonstrated that secreted bifunctional catalase-peroxidase is essential for the survival of the rice blast fungus Magnaporthe grisea during oxidative burst induced by theinfected plant (Tanabe et al., Mol. Plat. Microb. Inter. 2011.24:163–171). Magnaporthe grisea expresses several heme peroxidases and catalases of remarkable structural and functional variability.In this work we have focused on heme b containing catalase-peroxidases (KatGs). The fungus expresses an intracellularKatG most likely located in peroxisomes (MagKatG1) as wellas an extracellular variant that is secreted and might participatein host-pathogen interaction. Recombinant MagKatG1 and MagKatG2 have been expressed heterologously in E. coli and purified to homogeneity. We report UV–Vis and resonance Raman spectra of the ferric and ferrous forms as well as the standard reduction potential of the Fe(III)/ Fe(II) couple of both metalloproteins. Kinetic parameters of both catalase and peroxidase activities are reported probing several artificial one- and two electron donors at different pH. Both described KatGs differed slightly in their pH optima for both catalatic and peroxidatic reactions. For probing the peroxidatic reaction mode several (artificial) one and two electron donors (ascorbate, ABTS, 5-amino salicylic acid, L-DOPA, o-dianisidine, guaiacol, resorcinol, catechol, pyrogallol, luminol, tyrosine, tetramethylbenzidine and halides) were tested since the natural substrate is unknown. In addition ligand binding and reaction of the ferric enzymes with various hydrogen peroxide and peroxoacetic acid concentrations were tested by stopped-flow spectroscopy.Similarities and differences between these two KatGs and omologous heme peroxidases will be discussed and related to a putative role of KatG2 in plant-pathogen interaction
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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