A groundwater monitoring study was conducted as part of a comprehensive program to remediate a former wood-preserving site that was contaminated with creosote. Twenty-five multi-level samplers (MLSs) were installed on-site and groundwater samples were collected and tested regularly between March 1998 and July 2000. Nearly one-thousand hybrid poplar trees were planted on-site in 1997 to help contain the groundwater plume and enhance phytoremediation. Ten polycyclic aromatic hydrocarbons (PAHs) were monitored along with several terminal electron acceptors (TEAs) and their reduced end products. The focus of the study was to determine the extent of natural biodegradation in the subsurface and assess the role of the poplar trees in site remediation. Since monitoring began, considerable progress has been made remediating the site and the contaminant plume has been shrinking consistently. PAH levels in the groundwater and soil have been reduced and individual MLSs show consistently decreasing contamination. At this point in the study it cannot be conclusively determined what impact the poplar trees are having on the progressing site remediation. However, there is a wealth of evidence indicating that natural biodegradation is playing a major role in site cleanup. Monitoring of TEAs indicates suggests that there are aerobic zones in the site aquifer, but that reduced conditions exist as well. Dissolved oxygen (DO) was found in many MLS ports, but other ports were devoid of both DO and nitrate and contained large quantities of aqueous Fe(II). Oxygen, nitrate and Fe(III) are being reduced on-site and data suggests that they are being used in the biological oxidation of PAHs. Although laboratory studies document the oxidation of PAHs under sulfate-reducing conditions, high aqueous sulfate values were recorded throughout the site, regardless of the level of contamination. Several possible mechanisms are proposed to explain the coexistence of high sulfate and PAHs in the site aquifer. The system may be redox-buffered by excess solid Fe(III) and Mn(III, IV) oxides. Also, dissimilatory sulfate-reducers are strict anaerobes and oxygen-rich rainwater may be toxic to them. The presence of a layer of coal below land surface creates pyrite oxidation conditions similar to those encountered in conjunction with acid mine drainage. The MLSs most affected by the coal layer have less PAHs and DO, lower pH, and higher sulfate and Fe(II) levels than other wells. The oxidation-reduction status of each MLS, based on oxygen, nitrate and Fe(II) measurements, appears to be closely related to the level of PAH contamination, suggesting that PAHs are the primary substrate being biologically oxidized in the site aquifer. These findings tend to support the general belief that the major limitation to natural biodegradation in subsurface environments is the delivery of adequate supplies of suitable TEAs to contaminated zones. / Master of Science

This work investigated material corrosion by nuclear reactor coolants, including pressurized water reactor (PWR) coolant, boiling water reactor (BWR) coolant, high-temperature steam, lead-bismuth eutectic (LBE), and molten salt. Novel cladding materials for accident tolerant fuel (ATF) and additive manufacture (AM) Ni-based alloy were studied in water coolants. Similarly, the ATF material and Ni-based alloys were also examined under high-temperature steam to understand the corrosion behavior in beyond design basis accident (BDBA) scenarios. In addition to isothermal corrosion, stress corrosion cracking (SCC) and oxide layer in situ measurements were also conducted. Unlike conventional studies in liquid LBE that focused on Fe-based alloys, the present studies also investigated Ni-based alloys to explore the Ni content effects on the corrosion by LBE at high temperatures under saturated oxygen conditions. In molten salt environments, the corrosion behaviors of both Ni-based and Fe-based alloys were investigated. This study developed a redox potential range for mitigating corrosion by using a redox couple of UF4 /UF3 and a novel approach of potential measurements against F2/ F- potential experimentally. / Doctor of Philosophy / This work focuses on material degradation in harsh and extreme nuclear environments, including light water reactors and advanced reactors such as molten salt and liquid metal coolant reactors. Given the renewed interest in advanced nuclear reactors as a resource of clean energy, advanced material development, including structural, fuel, and coolant materials, has become a significant and trending research area. Based on our past experiences, we have seen the detrimental effects of material failure due to corrosion. Systems are inherently safe in the absence of material degradation. Nevertheless, this is an idealistic thought, as corrosion is inevitable. Therefore, this research focuses on corrosion mitigation, as absolute material preservation is impossible. This work includes corrosion studies in aqueous environments in light water reactors and advanced nuclear reactors under normal operation and extreme conditions such as accident environments. Much of this work provides insights into material corrosion behavior and mitigation that helps nuclear reactor operators ensure safe operations. Commercially available alloys such as SS316, Hast. X and Hast. N were examined in primary water, molten salt, high-temperature steam, and liquid bismuth environment and model Fe-Cr-Si alloys were investigated in water and steam to compare the corrosion mechanisms.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

No description available.

Les conditions redox des océans ont considérablement évolué au cours du Précambrien. Ceci est principalement dû à l’arrivée de l’oxygène engendrant dans un premier temps des oasis d’oxygène puis un Grand Évènement d’Oxydation (GEO) vers 2.45 Ga. Néanmoins, les connaissances concernant la datation des premiers signes d’oxygénation et les mécanismes de leur enregistrement sédimentaire, propres à cette période, restent encore à approfondir. Depuis plusieurs années, la composition isotopique en molybdène (δ98Mo) dans les sédiments est utilisée comme indicateur des conditions redox locales et globales des océans. Une étude élémentaire et isotopique en Mo des différentes phases constituant les carbonates a été réalisée suite à des attaques séquentielles sur des carbonates d’âge et d’environnement de dépôts différents. Les résultats montrent que le Mo se loge dans la phase organique mais également au sein des carbonates authigènes. Ces derniers influencent la valeur isotopique étudiée lors des attaques pseudo totales par 6N HCl et utilisée dans toutes les études du proxy redox des carbonates. Une étude minéralogique et isotopique du Mo des argiles et des carbonates riches en Mn (II) des Formations Boolgeeda et Kazput (craton de Pilbara, Australie) s’intéresse à la capacité du δ98Mo d’enregistrer les conditions redox locales afin de comprendre les mécanismes d’enrichissement sédimentaire en manganèse sur la période du GEO. Couplées à d’autre proxy redox et comparées à un analogue moderne (le bassin réduit de Landsort, mer Baltique), les données argumentent pour une réduction des oxydes de Mn(IV) au sein de la colonne d’eau et à l’interface des sédiments. Ces observations invitent à la discussion concernant les enrichissements en Mn du Précambrien dont le processus de réduction des oxydes est automatiquement considéré comme intrasédimentaire. Finalement, une étude compare des valeurs maximales en δ98Mo de carbonate analysées et compilées aux valeurs isotopiques des black shales et des formations de fer compilées au cours des temps géologiques en exploitant la composante globale de ce proxy redox. Les données suggèrent l’absence de condition euxinique permettant l’enregistrement des valeurs de l’eau de mer par les black shales. L’étude permet également d’observer la présence d’un cycle oxydatif du molybdène dès le Méso-Archéen. / The redox conditions of the oceans evolved considerably during the Precambrian. This is mainly due to the arrival of the oxygen, at first generating oxygen oases, and then accumulating in the atmosphere during the Great Oxidation Event (GOE) ca. 2.45 Ga. However, the earliest traces of free oxygen during these periods, and the mechanisms of their sedimentary expression, remain poorly understood. For over a decade, the isotopic composition of molybdenum (δ98Mo) in sediments has been used as a global marine redox proxy.An elemental and isotopic study of the different phases constituting carbonate rocks was carried out using sequential digestions performed on carbonates of different ages and depositional environments. The results show that Mo is primarily hosted in the organic phase but also within authigenic carbonate phases. These latter influence the isotopic value obtained during the classic pseudo-total digestion by 6N HCl that is most frequently employed for Mo isotope proxy studies in carbonates.Mineralogical and Mo isotopic studies on Mn(II)–rich shales and carbonates in the Boolgeeda and KazputFormations (Pilbara craton, Australia) leveraged the ability of δ98Mo to record local redox conditions in order to understand mechanisms responsible for sedimentary Mn enrichments occurring around the GOE. Coupled with other redox proxies and compared to modern analogues (e.g., the Landsort basin, Baltic Sea), the data argues for a reduction of Mn(IV) oxides within the water column and at the sediment-water interface. These observations bring new perspective on Precambrian Mn enrichments, which have been traditionally considered as the result of Mn oxide reduction occurring at depth in the sedimentary pile.Finally, a study of the maximum values of δ98Mo of analyzed and compiled carbonates compared to compiled isotopic values of black shales and iron formations deposited through geological time make use of the global component of this redox proxy. Data suggest an absence of euxinic conditions required for the recording of seawater values by black shales. This study also highlight the presence of an oxidative cycle of molybdenum since at least the Mesoarchean.

O conhecimento da paleoceanografia do Oceano Atlântico Sul tem aumentado nas últimas décadas, porém ainda são raros os trabalhos sobre o Atlântico Sudoeste que utilizam dados de proxies de condições redox de massas d\'água, relacionados às mudanças climáticas entre os períodos Pleistoceno superior e Holoceno. Diante disso, esta Dissertação de Mestrado avaliou as condições redox das águas intermediárias do Atlântico Sudoeste nos últimos 40 mil anos. Este trabalho fez estudos de proxies geoquímicos - de condições redox (V/Sc, V/Cr, V/Al, Mn/Al e Ni/Co), de aporte de sedimentos terTMTMrígenos (Fe/Ca e Ti/Ca), de produtividade (COT, CaCO3) e origem da matéria orgânica (δ13C e C/N) - em um registro sedimentar marinho coletado na região do talude continental da margem sudeste brasileira, e os relacionou com as mudanças da Célula de Revolvimento Meridional do Atlântico (sigla em inglês AMOC - Atlantic Medirional Overturning Circulation) e com os principais eventos climáticos em escala orbital, como o Último Máximo Glacial, e de escala milenar, como os eventos tipo Heinrich Stadials, Younger Dryas e 8.2. Os resultados demonstram que, nos últimos 40 mil anos, as águas intermediárias que banham a costa sudeste brasileira apresentam níveis óxicos, o que classifica o ambiente como oxidante, porém foi possível observar variações na quantidade de oxigênio dissolvido nessas águas durante determinados eventos climáticos, bem como variações no aporte de sedimentos terrígenos e na produtividade. Em escala orbital a insolação de verão do Hemisfério Sul e a variação do nível do mar, governadas pelo ciclo de precessão, apresentam-se como os principais mecanismos que influenciam essas variações. Em escala milenar a variabilidade da AMOC apresenta-se como o principal mecanismo responsável por essas variações. Dentre os eventos climáticos de escala milenar, o evento 8.2 demonstrou complexa variabilidade nas condições redox das águas intermediárias do Atlântico Sudoeste, uma vez que, durante sua ocorrência, observamos aumento das concentrações de oxigênio dessas águas e baixos valores de produtividade. / The interest in the paleoceanographic history of the South Atlantic Ocean has increased in the last decades, however there are still few studies regarding the redox conditions of the intermediate water masses of the Southwest Atlantic and their relationship to the climatic changes during the upper Pleistocene and Holocene. Within this context, this work aims to evaluate the redox conditions of the intermediate waters of the Southwest Atlantic in the last 40 ka. For this, geochemical proxies - of redox conditions (V/ Sc, V/ Cr, V/ Al, Mn/ Al and Ni/ Co), of terrigenous sediments supply (Fe/ Ca and Ti/ Ca), of productive (COT, CaCO3), and organic matter source (δ13C and C / N) - were applied to marine sediments from a core collected on the continental slope of the Brazilian Southeastern margin and then related it to changes in the Atlantic Meridional Overturning Circulation (AMOC) and with the main cold climatic events of North Atlantic, such as the Last Glacial Maximum and millennial scale, such as events type the Heinrich Stadials, Younger Dryas and 8.2. Our results show that, over the last 40,000 years, the redox conditions of the intermediate waters of the Brazilian Southeast margin present oxic levels, which classifies the environment as oxidant, however, variations was noticed in the amount of oxygen dissolved in these waters influenced by certain climatic events, as well as changes in the input of terrigenous sediments and in the productivity. In orbital scale, the summer insolation of the Southern Hemisphere and the variation of sea level, leaded by the cycle of precession, are presented as the main mechanisms that influence these variations. On the other hand, at millennia scale, the AMOC variability is the main mechanism responsible of these variations. Among the climate events at millennia scale, the event 8.2 demonstrated a complex variability of the redox conditions of the intermediate waters of the Southwest Atlantic, once during its occurrence we observed increase concentrations of oxygen in these waters and a decrease of productivity.

Nesta pesquisa são apresentados os resultados de uma investigação que teve como objetivo acessar o conhecimento docente de futuros professores de química, no contexto do Programa Institucional de Bolsa de Iniciação à Docência (Pibid). Esta pesquisa figura como um estudo de caso. Os dados se baseiam nas narrativas registradas por meio de gravações audiovisuais de três participantes da pesquisa durante as reuniões do subprojeto Pibid-química, regências e entrevistas semiestruturadas. Além destes, foram analisados relatórios, planos de aula, questionários dos pibidianos e um instrumento de percepção dos alunos da escola conveniada sobre o conhecimento docente dos licenciandos. Investigaram-se ainda os possíveis impactos do Pibid na formação da coordenadora e supervisora que orientaram os pibidianos. Buscou-se, por meio dos diversos documentos, indícios do conhecimento docente dos licenciandos bolsistas Pibid. A análise dos dados qualitativos teve como fundamentação teórica a análise de conteúdo, sendo as categorias provenientes do modelo do conhecimento base em conjunto com o modelo pentagonal. A análise do instrumento de percepção permeou métodos estatísticos. Para analisar as marcas deixadas pelo Pibid na formação da coordenadora e supervisora, adotaram-se as categorias do modelo conhecimento docente e outras emergentes. O pibidiano Antônio apresentou um bom conhecimento de conteúdo, de seus alunos e de suas limitações em relação ao conteúdo redox. Por outro lado, em algumas passagens das aulas, teve dificuldades em organizar a classe e o tempo de sua aula ao conteúdo. Antônio fez uso, em suas sequências didáticas, de diferentes instrumentos avaliativos. As suas estratégias de ensino se baseavam principalmente em práticas experimentais, na leitura, entre outros. A pibidiana Melissa demonstrou não dominar o conteúdo de reações redox, não ter conhecimento de currículo e de estratégias para desenvolver o conceito que ensinava. Grande parte dos conhecimentos docentes que emergiram dos documentos analisados da pibidiana foi reflexo das orientações que recebia das tutoras e também da experiência oportunizada pelo Pibid de como acessar as dificuldades dos alunos com o conteúdo específico, experimentar a gestão de classe e a organização de aulas. As avaliações adotadas pela pibidiana tinham por objetivo coletar dados para o subprojeto. Durante a sua regência não demonstrou uma preocupação com a aprendizagem dos alunos, mas em executar o currículo pretendido e aplicar as avaliações. O pibidiano Mateus demonstrou também limitações com o conteúdo e em selecionar os conceitos necessários para a aprendizagem dos discentes. Apresentou ainda dificuldades com a gestão do tempo e da classe. Por outro lado, passou a conhecer as barreiras conceituais dos discentes com o conteúdo redox, a partir de sua vivência no Pibid. Diversas das decisões sobre o fazer no ensino de ciências eleitas por Mateus foram orientações da supervisora. Pelo mapeamento infere-se que os conhecimentos para a docência acessados pelos pibidianos foram reflexo do Pibid personificado na figura das tutoras e pela experiência em sala. Evidenciou-se ainda que o Pibid vem contribuindo para a formação continuada da coordenadora, por possibilitar que a professora universitária conheça, por exemplo, a realidade da escola da educação básica; e da supervisora, por conceber-se como co-formadora dos licenciandos. Conclui-se que o conhecimento docente acessado por Mateus e Melissa foi influenciado pelas orientações da coordenadora. Acredita-se que o contato com o futuro ambiente profissional e a tutoria pelas docentes experientes oportunizaram aos pibidianos acessar os conhecimentos inerentes ao desenvolvimento do conhecimento base e do PCK. / This study presents the results of a research that aimed to access the teacher knowledge of future chemistry teachers, in the context of the Institutional Program for Scholarships for Initiation in Teaching (Pibid). This is a case study. Data were collected from audiovisual recordings of narratives from three participants during the Pibid-chemistry meetings, from regencies and from semi-structured interviews. In addition, Pibid-participants\' reports, lesson plans and questionnaires were analyzed, and an instrument that assessed the students\' perception about the teacher knowledge of the undergraduate students regarding teaching practices. The possible impacts of Pibid on the training of the coordinator and supervisor who guided the Pibid participants were also analyzed. Several documents were analyzed for evidence of the teacher knowledge of the Pibid students. The theoretical background for the analysis of qualitative data was based on content analysis, with categories from the base knowledge and the pentagonal model. The analysis of the students\' perception instrument was based on statistical methods. In order to analyze the marks left by Pibid in the training of the coordinator and supervisor, the study adopted the categories of teaching knowledge´model and other emerging ones. Pibid participant Antônio presented consistent content knowledge, students knowledge and students difficulties knowledge in relation to the redox content. On the other hand, in some occasions during classes, he had difficulties organizing the class and the content into the class time. Antônio used, in his didactic sequences, different evaluation instruments. His teaching strategies were based mainly on experimental practices, reading, among others. Pibid-participant Melissa demonstrated not master the redox reactions content, she did not have any knowledge about curricula and so could not develop strategies to work with the subject she taught. Much of the teaching knowledge that emerged from the documents analyzed from Melissa reflects the guidelines that she received from the coordinator and supervisor and from the experience offered by Pibid: how to access students\' difficulties with a specific content, how to deal with class management and organizing the classrooms. The assessment instruments adopted by Melissa were aimed at collecting data for the subproject. During her regency, she did not show concern for student learning, but in executing the intended curriculum and applying the assessments. Another Pibid participant, Mateus also seemed to have limited content knowledge and about selecting the necessary concepts for students learning. He also presented difficulties with time and class management. On the other hand, he came to understand the students\' conceptual difficulties with the redox content from his experience in Pibid. Several of the decisions that must be made in science education chosen by Mateus were guidelines given by his supervisor. From the mapping, it is inferred that the teaching knowledge accessed by the participants was a reflection of Pibid participation, personified in the figure of the tutor and by the experience in the classroom. It was also evidenced that Pibid contributes to the continued professional developing of the coordinator, by enabling university professors to know, for instance, the reality of basic education schools; and of supervisors, for conceiving themselves as co-teachers of the teaching students. The conclusion drawn is that the teaching knowledge accessed by Mateus and Melissa were influenced mainly by the coordinator\'s guidelines. It is believed that contact with their future work environment and tutoring by experienced teachers were fundamental for Pibid participants to access the knowledge inherent to the development of basic knowledge and the PCK.

O arsênio (As) é um semimetal,amplamente distribuído em toda a crosta terrestre, podendo ser encontrado em formas inorgânicas: arsenato (As5+) e arsenito (As3+) e orgânicas como a arsenobetaína (AsB), dimetil-arsênio (DMA) monometil-arsênio (MMA). As formas inorgânicas de As são mais tóxicas que as orgânicas. Patologias como hipertensão, diabetes e vários tipos de câncer estão associados com a exposição ao As inorgânico. Dentre as muitas fontes de exposição a este elemento químico, o arroz (Oryza sativa L.), tem sido destacado como uma das maiores fontes de exposição em populações não expostas diretamente ao As presente na água. Neste sentido, o objetivo deste trabalho foi avaliar a bioacessibilidade in vitro do As presente no arroz e avaliar em camundongos Swiss o acúmulo do semimetal nos tecidos bem como, possíveis alterações nos parâmetros redox em fígado e músculo decorrente do consumo de arroz contendo As. Para isto, na primeira etapa do estudo, o cultivar de arroz BR IRGA 409 foi plantado e divido em 2 grupos onde o primeiro foi chamado de As (-) (sem adição de As no solo) e outro plantado em solo contaminado com As na concentração de 10 mg/Kg, chamado de As (+). Após a colheita, foi verificado que o arroz do grupo As (+) apresentava uma maior concentração de As total no grão. Foram realizados testes de bioacessibilidade que demonstraram uma alta bioacessibilidade do As presente no arroz, principalmente das formas inorgânicas. Foram preparadas duas rações com o arroz plantado para administrar em 2 grupos de camundongos Swiss. Após o tratamento crônico por 100 dias, os amimais foram eutanasiados e coletados órgãos para avaliar o acúmulo do metaloide. Os tecidos que apresentaram um maior acúmulo de As foram bexiga, pelo, rim, baço, testículo, pele e fígado. Além disso, foram realizadas biópsias de músculo e tecido permeabilizados e determinação de parâmetros redox. Não foram observados diferenças estatísticas nas respirações do músculo e fígado. No entanto, observou-se, um aumento na formação de espécies reativas de oxigênio no fígado no grupo As (+), na presença de piruvato. Também foi demonstrado que nos animais expostos a uma maior concentração de As através da dieta ocorreu alterações na atividade enzimática e aumento da peroxidação lipídica. Finalmente, os resultados deste estudo demonstraram que o As inorgânico acumulado nos grãos de arroz se apresentam bioacessiveis e após a exposição pela dieta se distribuem por vários tecidos, levando a alterações em parâmetros redox no fígado. / Arsenic (As) is a metalloid, widely distributed throughout the Earth\'s crust. Arsenic. It can be found in inorganic forms such as (As5+) and arsenite (As3+) and organic compounds such as arsenobetaine (AsB), dimethyl-arsenic (DMA) and monomethylarsenic (MMA). Inorganic forms of As are more toxic than organic forms. Pathologies such as hypertension, diabetes and various types of cancer are associated with exposure to As inorganic. Among the many sources of exposure to this chemical element, rice (Oryza sativa L.) has been reported as the major source of human exposure in populations not exposed directly to As present in the water. In this sense, the objective of this study was to evaluate the in vitro bioaccessibility of As present in rice and to evaluate in Swiss mice the accumulation of semimetal tissues as well as possible changes in the redox parameters in liver and muscle of these animals by consumption of rice containing As by diet. For this, in the first stage of the study, rice cultivar BR IRGA 409 was planted and divided into 2 groups where the first was called As (-) (without addition of As in soil) and another planted in soil contaminated with As in concentration of 10 mg / kg, called As (+). After harvest, it was verified that the rice of the group As (+) had a higher concentration of As total in the grain. Bioaccessibility tests were performed that demonstrated a high bioaccessibility of As present in rice, mainly inorganic forms. Two feed were prepared with the planted rice to be administered in 2 groups of Swiss mice. After the chronic treatment for 100 days, the animals were euthanized and organs were collected to evaluate the accumulation of the metalloid. The tissues that presented a greater accumulation of As were bladder, hair, kidney, spleen, testicle, skin and liver. In addition, permeabilized muscle and tissue biopsies were performed and redox parameters were determined. No changes were observed on muscle and liver breathings. However, there is an increase in the formation of reactive oxygen species in the liver in the As (+) group in the presence of pyruvate. It has been also demonstrated that in animals exposed to a higher concentration of As through diet there were changes in enzymatic activity and increased lipid peroxidation. Finally, the results of this study demonstrated that the As inorganic accumulated in the rice grains are bioaccessible and after dietary exposure they are distributed through several tissues, leading to changes in redox parameters in the liver.

A ausência de XPC, uma proteína canonicamente envolvida em reparo de DNA por excisão de nucleotídeos, está associada a vários fenótipos característicos de disfunção mitocondrial como o desequilíbrio entre os complexos da cadeia transportadora de elétrons (CTE), redução no consumo de oxigênio, maior produção de peróxido de hidrogênio, e maior sensibilidade a agentes que causam estresse mitocondrial. Contudo, uma descrição mecanística da relação entre deficiência de XPC e disfunção mitocondrial ainda não está bem estabelecida. Aqui mostramos que a deficiência de XPC está associada ao aumento na expressão do supressor de tumor p53. Essa alteração é acompanhada pelo aumento da expressão de diversas proteínas que participam em importantes funções mitocondriais. A inibição de p53 reverte a superexpressão de algumas dessas proteínas. O tratamento com o inibidor do Complexo III da CTE antimicina A induz aumento da expressão de p53 de forma mais acentuada na linhagem Xpc-/-, enquanto o tratamento com o antioxidante N-acetilcisteína diminue a produção basal de H2O2, expressão de p53 e sensibilidade aumentada ao tratamento com antimicina A. Em conjunto, nossos resultados suportam a hipótese de que o aumento da produção de H2O2 em células Xpc-/- tem um papel causal na regulação da expressão de p53 e na disfunção mitocondrial / Although XPC has been initially implicated in the nucleotide excision DNA repair pathway, its deficiency is associated with mitochondrial dysfunction, including unbalanced electron transport chain (ETC) activity, lower oxygen consumption, increased hydrogen peroxide production, and greater sensitivity to mitochondrial stress. However, a mechanistic understanding of the role of XPC in regulating mitochondrial function is still not well established. Here we show that XPC deficiency is associated with increased expression of the tumor suppressor p53, which is accompanied by increased expression of several proteins that participate in important mitochondrial functions. Inhibition of p53 reverses the overexpression of some of these proteins. In addition, treatment with the ETC inhibitor antimycin A induces p53 expression more robustly in the Xpc-/- cells, while treatment with the antioxidant N-acetylcysteine decreases basal H2O2 production, p53 expression and sensitivity to antimycin A treatment. Together, our results support a model in which increased H2O2 production in Xpc-/- causes upregulation of p53 expression and mitochondrial dysfunction

Les peroxyrédoxines (Prx) sont des peroxydases à thiol, ubiquitaires, qui jouent un rôle central dans la physiologie du peroxyde d’hydrogène. Une famille de Prx dite "2-Cys-Prx typique" possède une propriété unique de suroxydation de la Cys catalytique sous forme acide sulfinique, qui constitue un mécanisme de régulation des fonctions des 2-Cys-Prx typiques en tant que peroxydase, capteur de peroxyde ou protéine chaperon. La réduction des 2-Cys-Prx typiques suroxydées est catalysée par la Sulfirédoxine (Srx), une sulfinyl réductase ATP-dépendante dont la constante catalytique est de l’ordre de 1-2 min-1, une valeur faible qui doit être corrélée au rôle de Srx dans la régulation redox. L’objectif de ce travail était d’analyser l’enzymologie de la régulation du système Prx/Srx au niveau, du processus de suroxydation des 2-Cys-Prx typiques, de l’étape limitante de la Srx, et de son recyclage par les systèmes redox cellulaires. Dans un premier temps, nous avons caractérisé les deux étapes du cycle catalytique de la 2-Cys-Prx typique majeure de S. cerevisiae Tsa1, dont la compétition contrôle la sensibilité à la suroxydation, par une stratégie combinant cinétiques rapides, système enzymatique couplé et modélisation cinétique. Ces travaux suggèrent que cette compétition est contrôlée par une réorganisation conformationnelle au cours du cycle catalytique de la Tsa1. Dans un second temps, l’étude de la première étape du mécanisme catalytique de Srx, qui consiste en l’activation ATP-dépendante du groupement acide sulfinique de la 2 Cys-Prx a permis, i) de montrer que l’étape limitante de la réaction catalysée par Srx était associée au processus chimique de transfert de phosphate, et ii) de proposer un modèle d’assemblage du complexe Michaelien Prx/Srx/ATP formé lors de ce processus. Enfin, par une approche combinant cinétiques enzymatiques in vitro et génétique de la levure in vivo, nous avons établi que le mécanisme de recyclage des Srx à 1 Cys existant chez les plantes ou les mammifères implique le rôle du glutathion comme réducteur cellulaire, contrairement à la Srx de S. cerevisiae qui est recyclée par le système thiorédoxine. De façon inattendue, la spécificité du glutathion dans ce mécanisme est assurée par un événement de reconnaissance au sein du complexe Prx/Srx / The peroxiredoxins (Prx) are ubiquitous thiol peroxidases, which play a central role in the physiology of hydrogen peroxide. A subclass of Prx called "typical 2-Cys-Prx" has a unique property to hyperoxidize the catalytic Cys into the sulfinic acid form, which acts as a regulation mechanism of their functions, as peroxidase, peroxide sensor or protein chaperone. The reduction of the overoxidized form is catalyzed by sulfiredoxin (Srx), an ATP-dependent sulfinyl reductase whose catalytic constant is about 1-2 min-1, a low value that must be correlated to the role of Srx in redox regulation. The aim of this study was to analyze the enzymology of the regulation of the Prx/Srx system at three diffrents points of control: the hyper-oxidation process of typical 2-Cys-Prx, the rate-limiting step of the Srx mechanism and the recycling step of Srx by the cellular thiol redox systems. We have first characterized the competition mechanism between the two steps of the catalytic mechanism of the major typical 2-Cys-Prx of S. cerevisiae, Tsa1, through a strategy combining rapid kinetics, coupled enzyme system and kinetic modelling analysis. This work suggests that the sensitivity to hyper-oxidation is controlled by a conformational reorganization during the catalytic cycle of Tsa1. Next, the study of the first step of Srx catalytic mechanism, which involves the ATP-dependent activation of the sulfinic acid form of typical 2-Cys Prx i) has shown that the rate-limiting step is associated with the chemical phosphate transfer process, and ii) provided an assembly model of the Michaelien complex Prx/Srx/ATP, formed during this process. Finally, through the combination of in vitro enzyme kinetics and in vivo yeast genetic tools, we established that the recycling mechanism of one Cys Srx, existing in plants or mammals, involves the glutathione (GSH) as reducer in cells, contrary to the Srx from S. cerevisiae, which is recycled by the Thioredoxin system. Unexpectedly, our study suggests that GSH binds the thiolsulfinate complex, confirming the role of GSH as the primary reducing system of 1-Cys-Srx