1,720,958 research outputs found
Une Multi Copper Oxidase commercial modèle ultime de photosynthèse artificielle
No full textElectron transfer (ET) reactions are fundamental in biological processes like photosynthesis. In a simple enzymatic model like a Multi Copper Oxidase, four reducing equivalents (and four protons) are transiently stored to reduce O2 from air that is a safe, renewable, and inexpensive e- acceptor. In this thesis, we explore ET processes within the high-potential fungal laccase LAC3 (an archetypal MCO) and some of its variants, investigating responses to substrates, inhibitors, and especially light. Our initial endeavors focused on characterizing LAC3 under catalytic conditions, unraveling ET processes connecting intermediate redox states and their associated rates. We uncovered as well a protective mechanism enabling the enzyme under oxidative stress to convert the harmful O2⋅– radical into H2O, prolonging its longevity. Inspired by photosynthesis, we engineered LAC3 by covalently attaching photosensitizers – either a Ru2+-polypyridyl complex or a zinc porphyrin – to various surface grafting points. This approach not only links light-triggered oxidation of substrates to complete O2 reduction but also offers valuable means to probe productive and deleterious ET pathways from the enzyme surface to the copper redox sites. We studied the effects that distance separating the sensitizers from the copper centers, electronic coupling and the polypeptide matrix may have on photoinduced ET processes. These investigations deepen our understanding on ET in metalloenzymes, offering potential for innovative tools in sustainable multielectronic photochemical transformations.Les réactions de transfert d'électrons (ET) sont fondamentales dans les processus biologiques comme la photosynthèse. Dans un modèle simple tel qu'une Multi Copper Oxidase, quatre e- (& 4H+) sont stockés transitoirement pour réduire l'O2 de l'air, un accepteur d'e- sûr, renouvelable et peu coûteux. Dans cette thèse, nous explorons les processus ET au sein d’une MCO fongique, LAC3 et de certaines de ses variantes, en examinant leurs réponses aux substrats, aux inhibiteurs et à la lumière. Nos premiers efforts ont portés sur la caractérisation de LAC3 dans des conditions catalytiques, décrivant les processus ET qui relient les états redox intermédiaires et leurs vitesses associés. Nous avons découvert un mécanisme de protection contre un stress oxydant permettant à l'enzyme de convertir efficacement le radical nocif O2⋅– en H2O, prolongeant ainsi sa longévité. Inspirés par la photosynthèse naturelle, nous avons modifié les enzymes en fixant de manière covalente des photosensibilisateurs - un complexe Ru2+-polypyridyl ou une porphyrine de zinc - à différents points de greffage en surface. Cette approche relie non seulement l’oxydation des substrats déclenchée par la lumière à la réduction complète de l’O2, mais offre des moyens précieux pour sonder les voies ET productives et délétères depuis la surface de l'enzyme jusqu'aux centres redox. Nous avons étudié les effets que la distance entre le sensibilisateur et les centres cuivre, le couplage électronique et la nature de la matrice peptidique peuvent avoir sur les processus de ET photo-induits. Ces investigations ont renforcé notre compréhension du transport d'e- dans les métalloenzymes, offrant des perspectives pour des outils innovants dans les transformations photochimiques multi-électroniques durables
Une oxydase multicuivre comme modèle ultime de photosynthèse artificielle
No full textLes réactions de transfert d'électrons (ET) sont fondamentales dans les processus biologiques comme la photosynthèse. Dans un modèle simple tel qu'une Multi Copper Oxidase, quatre e- (& 4H+) sont stockés transitoirement pour réduire l'O2 de l'air, un accepteur d'e- sûr, renouvelable et peu coûteux. Dans cette thèse, nous explorons les processus ET au sein d’une MCO fongique, LAC3 et de certaines de ses variantes, en examinant leurs réponses aux substrats, aux inhibiteurs et à la lumière. Nos premiers efforts ont portés sur la caractérisation de LAC3 dans des conditions catalytiques, décrivant les processus ET qui relient les états redox intermédiaires et leurs vitesses associés. Nous avons découvert un mécanisme de protection contre un stress oxydant permettant à l'enzyme de convertir efficacement le radical nocif O2⋅– en H2O, prolongeant ainsi sa longévité. Inspirés par la photosynthèse naturelle, nous avons modifié les enzymes en fixant de manière covalente des photosensibilisateurs - un complexe Ru2+-polypyridyl ou une porphyrine de zinc - à différents points de greffage en surface. Cette approche relie non seulement l'oxydation des substrats déclenchée par la lumière à la réduction complète de l’O2, mais offre des moyens précieux pour sonder les voies ET productives et délétères depuis la surface de l'enzyme jusqu'aux centres redox. Nous avons étudié les effets que la distance entre le sensibilisateur et les centres cuivre, le couplage électronique et la nature de la matrice peptidique peuvent avoir sur les processus de ET photo-induits. Ces investigations ont renforcé notre compréhension du transport d'e- dans les métalloenzymes, offrant des perspectives pour des outils innovants dans les transformations photochimiques multi-électroniques durablesElectron transfer (ET) reactions are fundamental in biological processes like photosynthesis. In a simple enzymatic model like a Multi Copper Oxidase, four reducing equivalents (and four protons) are transiently stored to reduce O2 from air that is a safe, renewable and inexpensive e- acceptor. In this thesis, we explore ET processes within the high-potential fungal laccase LAC3 (an archetypal MCO) and some of its variants, investigating responses to substrates, inhibitors, and especially light. Our initial endeavors focused on characterizing LAC3 under catalytic conditions, unraveling ET processes connecting intermediate redox states and their associated rates. We uncovered as well a protective mechanism enabling the enzyme under oxidative stress to convert the harmful O2⋅– radical into H2O, prolonging its longevity. Inspired by photosynthesis, we engineered LAC3 by covalently attaching photosensitizers – either a Ru2+-polypyridyl complex or a zinc porphyrin – to various surface grafting points. This approach not only links light-triggered oxidation of substrates to complete O2 reduction but also offers valuable means to probe productive and deleterious ET pathways from the enzyme surface to the copper redox sites. We studied the effects that distance separating the sensitizers from the copper centers, electronic coupling and the polypeptide matrix may have on photoinduced ET processes. These investigations deepen our understanding on ET in metalloenzymes, offering potential for innovative tools in sustainable multielectronic photochemical transformation
Une Multi Copper Oxidase commercial modèle ultime de photosynthèse artificielle
No full textElectron transfer (ET) reactions are fundamental in biological processes like photosynthesis. In a simple enzymatic model like a Multi Copper Oxidase, four reducing equivalents (and four protons) are transiently stored to reduce O2 from air that is a safe, renewable, and inexpensive e- acceptor. In this thesis, we explore ET processes within the high-potential fungal laccase LAC3 (an archetypal MCO) and some of its variants, investigating responses to substrates, inhibitors, and especially light. Our initial endeavors focused on characterizing LAC3 under catalytic conditions, unraveling ET processes connecting intermediate redox states and their associated rates. We uncovered as well a protective mechanism enabling the enzyme under oxidative stress to convert the harmful O2⋅– radical into H2O, prolonging its longevity. Inspired by photosynthesis, we engineered LAC3 by covalently attaching photosensitizers – either a Ru2+-polypyridyl complex or a zinc porphyrin – to various surface grafting points. This approach not only links light-triggered oxidation of substrates to complete O2 reduction but also offers valuable means to probe productive and deleterious ET pathways from the enzyme surface to the copper redox sites. We studied the effects that distance separating the sensitizers from the copper centers, electronic coupling and the polypeptide matrix may have on photoinduced ET processes. These investigations deepen our understanding on ET in metalloenzymes, offering potential for innovative tools in sustainable multielectronic photochemical transformations.Les réactions de transfert d'électrons (ET) sont fondamentales dans les processus biologiques comme la photosynthèse. Dans un modèle simple tel qu'une Multi Copper Oxidase, quatre e- (& 4H+) sont stockés transitoirement pour réduire l'O2 de l'air, un accepteur d'e- sûr, renouvelable et peu coûteux. Dans cette thèse, nous explorons les processus ET au sein d’une MCO fongique, LAC3 et de certaines de ses variantes, en examinant leurs réponses aux substrats, aux inhibiteurs et à la lumière. Nos premiers efforts ont portés sur la caractérisation de LAC3 dans des conditions catalytiques, décrivant les processus ET qui relient les états redox intermédiaires et leurs vitesses associés. Nous avons découvert un mécanisme de protection contre un stress oxydant permettant à l'enzyme de convertir efficacement le radical nocif O2⋅– en H2O, prolongeant ainsi sa longévité. Inspirés par la photosynthèse naturelle, nous avons modifié les enzymes en fixant de manière covalente des photosensibilisateurs - un complexe Ru2+-polypyridyl ou une porphyrine de zinc - à différents points de greffage en surface. Cette approche relie non seulement l’oxydation des substrats déclenchée par la lumière à la réduction complète de l’O2, mais offre des moyens précieux pour sonder les voies ET productives et délétères depuis la surface de l'enzyme jusqu'aux centres redox. Nous avons étudié les effets que la distance entre le sensibilisateur et les centres cuivre, le couplage électronique et la nature de la matrice peptidique peuvent avoir sur les processus de ET photo-induits. Ces investigations ont renforcé notre compréhension du transport d'e- dans les métalloenzymes, offrant des perspectives pour des outils innovants dans les transformations photochimiques multi-électroniques durables
De Novo design of α-helical heme binding proteins capable of versatile cofactor ligation
No full textInternational audienceDe novo design of artificial metalloproteins offers a powerful approach to dissect and mimic the diverse and exquisite coordination environments found in natural heme proteins. These designed heme proteins seek to replicate the broad array of metabolic, regulatory, and structural functions that hemes perform in biological systems. In this chapter, we present an amenable methodology for the preparation and characterization of de novo-designed heme-binding coiled coils featuring either His- and/or Cys-based axial ligation, which mimic the redox active sites of peroxidases, chloroperoxidases, and cytochrome P450 monooxygenases. The ability to reversibly control heme coordination and spin state through pH variations within a single scaffold provides novel insights into the principles governing catalysis in heme-containing and heme-binding proteins and paves the groundwork for engineering versatile catalysts with tailored reactivity
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
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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