1,721,512 research outputs found
Microwave-assisted hydrothermal synthesis of αβ-Ni(OH)2 nanoflowers on nickel foam for ultra-stable electrodes of supercapacitors
No full textData for publication entitled “Microwave-assisted hydrothermal synthesis of αβ-Ni(OH)2 nanoflowers on nickel foam for ultra-stable electrodes of supercapacitors” by Muhammad Saleem Akhtar, Tomasz Wejrzanowski , Gabriela Komorowska , Bogusława Adamczyk-Cieślak , Emilia Choinska obtained within the National Science Centre (Poland), OPUS project Grant number (2022/45/B/ST5/02450). The dataset contains raw data of physicochemical and electrochemical performance of nickel hydroxide in different phasis.For more details, please refer to the README file.</p
A review of 18O labelling studies to probe the mechanism of aromatase (CYP191A)
No full textOur previous studies, using precursors for two classes of estrogens, estrone and estriol, have highlighted the following facets of aromatase. The overall reaction, converting androgens into estrogens, occurs in three steps, each requiring NADPH and O
2. In Step 1, a 19-hydroxy intermediate is produced, which in Step 2, is converted into a 19-oxo derivative via a gem -diol intermediate with the stereospecific loss of H
Re. In Step 3, a scission of the C-10-C-19 bond occurs releasing C-19 as formic acid (HCOOH) and incorporating an atom of oxygen from O
2, The other oxygen atom of formic acid is derived from the hydroxyl group introduced in Step 1. These experiments were performed using the classical placental microsomal system. Our findings were confirmed and extended by (the late) Caspi's group. However, incorporation of oxygen in Step 3, has been challenged in a subsequent study using a soluble reconstituted system. The latter authors have implied the superiority of their system over the microsomal preparation. However, several assumptions under pinning their own work were derived from the use of placental microsomes. Furthermore, the authors have not considered that when a previous work is challenged it needs to be repeated under the conditions described in the original publication.
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A review of mechanistic studies on aromatase (CYP19) and 17?-hydroxylase-17,20-lyase (CYP17)
No full textIn the conventional P-450 dependent hydroxylation reaction, the FeIII resting state of the enzyme, by a single electron transfer, is reduced to FeII, which reacts with O2 to produce a FeIII–O–O intermediate. The latter following the transfer of another electron furnishes a ferric-peroxyanion, FeIII–O–O?, which after protonation leads to the fission of the O–O bond resulting in the formation of FeVO, the key player in the hydroxylation process. Certain members of the P-450 family, including CYP17 and CYP19, catalyze, at the same active site, not only the hydroxylation process but also an acyl–carbon bond cleavage reaction which has been interpreted to involve the nucleophilic attack of the ferric-peroxyanion, FeIII–O–O?, on the acyl carbon to furnish a tetrahedral intermediate which fragments, leading to acyl–carbon cleavage. Evidence is presented to show that in the case of CYP17 the attack of FeIII–O–O? on the target carbon is promoted by cytochrome b5, which acts as a conformational regulator of CYP17. It is this regulation of CYP17 that provides a safety mechanism which ensures that during corticoid biosynthesis, which involves 17?-hydroxylation by CYP17, androgen formation is avoided. Finally, a brief account is presented of the inhibitors, of the two enzymes, which have been designed on the basis of their mechanism of action
Pcal_1311, an alcohol dehydrogenase homologue from Pyrobaculum calidifontis, displays NADH-dependent high aldehyde reductase activity
No full textGenome sequence of Pyrobaculum calidifontis, a hyperthermophilic archaeon, harbors three open-reading frames annotated as alcohol dehydrogenases. One of them, Pcal_1311, does not display a significantly high homology with any of the characterized alcohol dehydrogenases. Highest homology of 38% was found with the characterized counterpart from Geobacillus stearothermophilus. To examine the biochemical properties of Pcal_1311, we have cloned and functionally expressed the gene in Escherichia coli. Purified recombinant Pcal_1311 catalyzed the NAD(H)-dependent oxidation of various alcohols and reduction of aldehydes, with a marked preference for substrates with functional group at the terminal carbon. Highest activity for the oxidation reaction (3 μmol min−1 mg−1) was found with 1,4-butanediol and for the reduction reaction (150 μmol min−1 mg−1) with glutaraldehyde. Both the oxidation and reduction activities increased with the increase in temperature up to 80 °C. Recombinant Pcal_1311 was highly stable and retained more than 90% activity even after incubation of 180 min at 90 °C. In addition to the thermostabilty, Pcal_1311 was highly stable in the presence of known denaturants including urea and guanidine hydrochloride. The high stability, particularly thermostability, and the NADH-dependent aldehyde reduction activity make Pcal_1311 a unique member in the alcohol dehydrogenase family
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
Inventory of ‘slow exchanging’ hydrogen atoms in human proinsulin and its derivatives: observations on the mass spectrometric analysis of deuterio-proteins in D2O
No full textSecondary structure elements of human proinsulin and of its tryptic products were compared by H/D exchange, in a single-pot, using mass spectrometry. Human proinsulin containing an N-terminal methionine, M-proinsulin, was engineered and converted into a perdeuterio derivative, which using an optimized mass spectrometric protocol and manual calculations gave a mass of 9669.6 (± 1) Da showing the replacement, with deuterium of 146.4 from a total of 149 exchangeable hydrogen atoms (83 from amides and 66 from side-chains). Tryptic digestion of the perdeuterio-M-proinsulin, followed by the transfer of the digest from a deuterio- into a protio-medium showed, at the earliest time of analysis, that of the 27 (± 1) D atoms retained in M-proinsulin, 24 (± 1) were found in the insulin nucleus, M-insulin-RR, and 4.2 (± 1) in the C-peptide-KR. A temporal analysis of the fate of D atoms in these species showed that whereas the C-peptide-KR rapidly exchanged its deuterium, losing all by 6 h, the loss of D atoms from M-proinsulin and M-insulin-RR was gradual and in each case, 12 deuterium atoms survived exchange for 72 h. At all time intervals the loss of D atoms from M-proinsulin mirrored that from M-insulin-RR plus the C-peptide-KR, suggesting that the secondary-structure elements of M-proinsulin are largely conserved in its two component parts
The reverse gyrase from Pyrobaculum calidifontis, a novel extremely thermophilic DNA topoisomerase endowed with DNA unwinding and annealing activities
No full textReverse gyrase is a DNA topoisomerase specific for hyperthermophilic bacteria and archaea. It catalyzes the peculiar ATP-dependent DNA-positive supercoiling reaction and might be involved in the physiological adaptation to high growth temperature. Reverse gyrase comprises an N-terminal ATPase and a C-terminal topoisomerase domain, which cooperate in enzyme activity, but details of its mechanism of action are still not clear. We present here a functional characterization of PcalRG, a novel reverse gyrase from the archaeon Pyrobaculum calidifontis. PcalRG is the most robust and processive reverse gyrase known to date; it is active over a wide range of conditions, including temperature, ionic strength, and ATP concentration. Moreover, it holds a strong ATP-inhibited DNA cleavage activity. Most important, PcalRG is able to induce ATP-dependent unwinding of synthetic Holliday junctions and ATP-stimulated annealing of unconstrained single-stranded oligonucleotides. Combined DNA unwinding and annealing activities are typical of certain helicases, but until now were shown for no other reverse gyrase. Our results suggest for the first time that a reverse gyrase shares not only structural but also functional features with evolutionary conserved helicase-topoisomerase complexes involved in genome stability
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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