1,720,985 research outputs found
EFFECT OF THE gammaM23-K MUTATION ON ATP SYNTHASE ACTIVATION BY THE PROTONMOTIVE FORCE AND ON COUPLING ATP HYDROLYSIS TO PROTON TRANSLOCATION
No full textThe single-site mutation M23-K in the gamma-subunit of the E.coli ATP synthase has been
reported to perturb the energetic coupling between F1 and FO and to increase the transition state
activation energy for ATP hydrolysis (1). We have introduced the homologous mutation gamma-
M23-K in the ATP synthase of Rhodobacter capsulatus in order to study its phenotype by taking
advantage of the photosynthetic system.
In our hands, the most striking phenotypic difference to the wild-type complex was found in the
ATP hydrolysis activation by the protonmotive force. The higher ATP hydrolysis rate is best
observed when the activating protonmotive force is dissipated by addition of uncouplers. At low or
zero protonmotive force, though, this activated state decays and can be measured only for a limited
time. We have found that in the mutated enzyme, the half-life time of the light-activated state,
measured under the above conditions, is reduced from 13 to 4 s. Moreover, after a burst of ATP
synthesis triggered by a train of flashes, while the wild-type rapidly hydrolyzes the newly
synthesized ATP, the mutant does not, indicating that stabilization of the inactive state is even
higher at low ATP concentration.
The efficiency of proton coupling could be modified, both in the wild type (2) and mutated
strain according to the experimental conditions. While a large difference in efficiency could be
detected in the M23K mutated strain as compared to the wild type under certain conditions, in other
cases the difference was much more limited. A detailed analysis of the two phenotypes will be
presented and discussed in relation to the modulation of proton pumping activity and the possible
differences produced by the mutation.
(1) Al-Shawi MK, Ketchum CJ, Nakamoto RK.. (1997) J. Biol. Chem. 272: 2300-6.
(2) Turina P., Giovannini D., Gubellini F. and Melandri B.A. (2004) Biochemistry 43: 11126-34
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
A point mutation in the ATP synthase of Rhodobacter capsulatus results in differential contributions of ΔpH and Δφ in driving the ATP synthesis reaction
No full textThe interface between the c-subunit oligomer and the a subunit in the F0 sector of the ATP synthase is believed to form the core of the rotating motor powered by the protonic flow. Besides the essential cAsp61 and aArg210 residues (Escherichia coli numbering), a few other residues at this interface, although nonessential, show a high degree of conservation, among these aGlu219. The homologous residue aGlu210 in the ATP synthase of the photosynthetic bacterium Rhodobacter capsulatus has been substituted by a lysine. Inner membranes prepared from the mutant strain showed approximately half of the ATP synthesis activity when driven both by light and by acid-base transitions. As estimated with the ACMA assay, proton pumping rates in the inner membranes were also reduced to a similar extent in the mutant. The most striking impairment of ATP synthesis in the mutant, a decrease as low as 12 times as compared to the wild-type, was observed in the absence of a transmembrane electrical membrane potential (Δφ) at low transmembrane pH difference (ΔpH). Therefore, the mutation seems to affect both the mechanism responsible for coupling F1 with proton translocation by F0, and the mechanism determining the relative contribution of ΔpH and Δφ in driving ATP synthesis
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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