1,720,959 research outputs found
Reaction of nitric oxide with the oxidized di-heme and heme-copper oxygen-reducing centers of terminal oxidases: Different reaction pathways and end-products.
No full textInhibition of terminal oxidases by nitric oxide (NO) has been extensively investigated as it plays a role in regulation of cellular respiration and pathophysiology. Cytochrome bd is a tri-heme (b(558), b(595), d) bacterial oxidase containing no copper that couples electron transfer from quinol to O(2) (to produce H(2)O) with generation of a transmembrane protonmotive force. In this work, we investigated by stopped-flow absorption spectroscopy the reaction of NO with Escherichia coli cytochrome bd in the fully oxidized (O) state. We show that under anaerobic conditions, the O state of the enzyme binds NO at heme d with second-order rate constant k(on)=1.5+/-0.2x10(2) M(-1) s(-1), yielding a nitrosyl adduct (d(3+)-NO or d(2+)-NO(+)) with characteristic optical features (an absorption increase at 639nm and a red shift of the Soret band). The reaction mechanism is remarkably different from that of O cytochrome c oxidase in which the heme-copper binuclear center reacts with NO approximately three orders of magnitude faster, forming nitrite. The data allow us to conclude that in the reaction of NO with terminal oxidases in the O state, Cu(B) is indispensable for rapid oxidation of NO into nitrite
Cytochrome bd oxidase and bacterial tolerance to oxidative and nitrosative stress
No full textCytochrome bd is a prokaryotic respiratory quinol:O2 oxidoreductase, phylogenetically unrelated to the extensively studied heme-copper oxidases (HCOs). The enzyme contributes to energy conservation by generating a proton motive force, though working with a lower energetic efficiency as compared to HCOs. Relevant to patho-physiology, members of the bd-family were shown to promote virulence in some pathogenic bacteria, which makes these enzymes of interest also as potential drug targets. Beyond its role in cell bioenergetics, cytochrome bd accomplishes several additional physiological functions, being apparently implicated in the response of the bacterial cell to a number of stress conditions. Compelling experimental evidence suggests that the enzyme enhances bacterial tolerance to oxidative and nitrosative stress conditions, owing to its unusually high nitric oxide (NO) dissociation rate and a notable catalase activity; the latter has been recently documented in one of the two bd-type oxidases of Escherichia coli. Current knowledge on cytochrome bd and its reactivity with O2, NO and H2O2 is summarized in this review in the light of the hypothesis that the preferential (over HCOs) expression of cytochrome bd in pathogenic bacteria may represent a strategy to evade the host immune attack based on production of NO and reactive oxygen species (ROS)
Catalytic intermediates of cytochrome bd terminal oxidase at steady-state
No full textThe cytochrome bd ubiquinol oxidase from Escherichia coli couples the exergonic reduction of O2 to 2H2O to proton motive force generation by transmembrane charge separation. The oxidase contains hemes b558 and b595 and heme d, where O2 chemistry occurs through sequential formation of a few catalytic intermediates. The steady-state behavior of the isolated cytochrome bd has been examined by stopped-flow multiwavelength absorption spectroscopy. Under turnover conditions sustained by O2 and dithiothreitol-reduced ubiquinone, we found [1] that the mostly populated catalytic intermediates are the ferryl and oxy-ferrous species, with a minor fraction of the enzyme containing ferric heme d and possibly one electron on heme b558. These new findings clearly differ from those obtained with mammalian cytochrome c oxidase [2], in which the oxygen intermediates were not found to be populated at detectable levels under similar conditions. The results are discussed in the light of previously proposed models of the cytochrome bd catalytic cycle
Unusually fast ligand dissociation from bacterial cytochrome bd: A clue to NO tolerance?
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Nitric Oxide reacts with the ferryl-oxo catalytic intermediate of the CuB-lacking cytochrome bd terminal oxidase
No full textCytochrome bd is a bacterial respiratory oxidase carrying three hemes but no copper. We show that nitric oxide (NO) reacts with the intermediate F of cytochrome bd from Azotobacter vinelandii: (i) with a 1:1 stoichiometry, (ii) rapidly (k=1.2 +/- 0.1 x 10(5)M(-1)s(-1) at 20 degrees C), and (iii) yielding the oxidized enzyme with nitrite bound to heme d at the active site. Unexpectedly, the NO reaction mechanism of this catalytic intermediate in the Cu(B)-lacking cytochrome bd appears similar to that of beef heart cytochrome c oxidase, where Cu(B) was proposed to play a key role
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
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