Uno de los objetivos fundamentales de la mejora de trigo duro es la obtención devariedades que tengan un gluten fuerte y elástico, satisfactorio para la producción depastas de alta calidad. Para tal fin, una estrategia es la Incorporación de materialgenético de otras especies próximas al trigo duro.En trigo harinero se han dedicado muchos esfuerzos a la obtención de genotipos con latranslocación 1BL/1R5, que se relaciona con mejores características agronómicas, talescomo resistencia a enfermedades y un mayor rendimiento. Debido a ello en el CentroInternacional de Mejoramiento de Maíz y Trigo (CIMMYT) se ha Incorporado latranslocación 1E5L/1R5 al trigo duro. Sin embargo, la Influencia de dicha translocación enesta especie, tanto en sus características agronómicas como en la calidad, es pococonocida. Por ello, el siguiente trabajo se planteó con el objetivo principal de evaluar lasdiferencias que presentan los trigos duros con translocación 1E3L/1RS procedentes delcultivar Altar 04, en algunas características agronómicas, bioquímicas y de calidad.El material vegetal que se utilizó en este trabajo fue obtenido por CIMMYT, evaluándoseocho líneas isogénicas, cuatro de ellas con la translocación cromosómica 1E5L/1RS (1RS) yotras cuatro sin dicha translocación (1EJS), además de incluir el progenitor Altar 04 y alcultivar Vltrón como testigo local.Los ensayos se realizaron en dos ambientes de México 1993-94 (uno con cinco riegos yotro con un riego) y en cuatro ambientes de España durante los ciclos 1994-95 y 1995-96 (Torregrossa 1994-95 y 1995-96, La Tallada 1995-96 y Jerez de la Frontera 1995-96). Además, en el ciclo 1995-96 se realizaron tres ensayos de fertilización nitrogenadacon tres niveles de nitrógeno: Control (50 UNF/ha de N en presiembra + 6>0 UFN/ha enencañado), Fraccionada (5O UFN/ha en presiembra + 30 UFN/ha encañado + 50 UFN/haen antesis) y Baja (5O UFN/ha en presiembra + 3O UFN/ha en encañado).La evaluación agronómica de los materiales sembrados se basó en el rendimiento y suscomponentes. La Influencia de la translocación en la calidad se analizó a partir dedeterminaciones relacionadas con aspectos físicos y físico-químicos del grano, -conanálisis reológicos de las masas, con observaciones sobre la elaboración y cocción delespagueti y con una evaluación de la estructura física del gluten por microscopía debarrido. Por último, se realizó una evaluación bioquímica de las proteínas de reserva delgrano y gluten.Los resultados de la evaluación agronómica Indicaron que el ambiente fue el factordeterminante en la variabilidad de los parámetros medidos, for otra parte, no sedetectaron diferencias claras entre las líneas isogénicas 1RS y 155, ya que, si bienexistieron valores medios significativamente mayores en n° de espigas/m2 y n° de granos/m2en los 1155, el peso de mil granos fue significativamente mayor en los 1RS. Estopudo influir en que se produjera un efecto compensatorio de tal forma que no existierondiferencias significativas en rendimiento de grano entre genotipos 155 y 1RS. Por otraparte, no se encontró una influencia clara de la fertilización nitrogenada en el rendimientoy sus componentes.En las características físicas del grano, aunque en algunos parámetros se encontrarondiferencias significativas entre los genotipos 1E5S y 1RS, las magnitudes fueron pequeñasy variaron significativamente entre los ambientes y tratamientos de fertilizaciónnitrogenada, por lo cual no se encontró una ventaja clara y apreciablemente grande de lapresencia del brazo 1RS en calidad física del grano de trigo duro.En las determinaciones físico-químicas y reológicas realizadas, sólo en Intensidad delcolor amarillo y cantidad de proteínas los 1RS mostraron valores mayores a los genotipos155. En otros, como cantidad e índice de gluten, volumen de sedimentación, propiedadesde mezclado, características alveográficas y textura de masas, los genotipos 1RSmostraron una calidad significativamente inferior en comparación a los genotiposnormales. Resultados similares se obtuvieron en la evaluación fíe la cocción delespaguetti. Además, los niveles de calidad mostrados por los genotipos 1RS fue tal queharía difícil su aprovechamiento en la elaboración de pastas y otros posibles productos.La calidad Inferior de las isolíneas 1RS también se puso de manifiesto en la estructurafísica del gluten, la cual se analizó en un microscopio electrónico de barrido, donde seobservó que el gluten del trigo 155 posee una estructura tridimensional apreciablementemás compacta, cerrada y continua que la estructura de los genotipos 1RS.La calidad inferior de los líneas Isogénlcas con translocación 1E5L/1RS (1RS) se explicó através de los resultados obtenidos en el análisis bioquímico de la proteínas de reserva. Enel fraccionamiento de las proteínas por SDS-PAGE y A-PAGE, mientras las líneasIsogénlcas normales (1BS) mostraron tener las subunldades de proteínas codificadas porel loci Glu-£>3/GI¡-&1, las líneas Isogénlcas 1RS en todo momento carecieron de éstas.Memas, por el fraccionamiento y cuantlflcaclón de las proteínas por RP-HPLC, seencontró que la fracción Glu LMW-6> marcó la principal diferencia cuantitativa entregenotipos 1B5 y 1RS. Como promedio de los valores medios de los ensayos, los genotipos1RS tuvieron 26% de las Glu LMW-& halladas en los genotipos 155.Así pues, con base a los resultados de este trabajo se puede concluir que la calidadinferior de los trigos duros con la translocación 1BL/1R5 fue principalmente determinadapor la carencia de las subunldades Glu LMW-B> codificadas por el locus Glu 03, las cualesrepresentaron un proporción Importante de las proteínas de reserva de los trigos durosnormales estudiados.

Yellow pigment (YP) concentration is an important quality trait in durum wheat (<i>Triticum turgidum</i> L. var <i>durum</i>) and is comprised primarily of carotenoids. The main objective of our study was to measure the accumulation of carotenoids during the grain fill period to improve our understanding of the physiological basis for differences among durum wheat cultivars. Thirteen cultivars and breeding genotypes with large variation in total YP concentration (<6 µg g-1 to >15 µg g-1) were studied. Spikes were sampled from replicated field plots in 2007 and 2008 near Saskatoon and Swift Current, Saskatchewan, Canada, at 14, 21, 28 and 35 days after heading (DAH). The remainder of each plot was combined at grain maturity for YP and carotenoid analysis. Carotenoids were extracted with 1:1 methanol:dichloromethane (0.1% BHT) and quantified with HPLC. <i>Trans</i> (E)-lutein was the predominant carotenoid at maturity and was detected at 14 DAH in all genotypes. The rate and duration of E-lutein accumulation was variable among genotypes expressing high, intermediate and low YP. The accumulation of all carotenoids was lowest in genotypes expressing low YP, and suggests rate limitations early in the carotenoid biosynthetic pathway. E-zeaxanthin concentrations were highest in mature grain, but no significant differences were detected among genotypes. However, the ratio of E-zeaxanthin to E-lutein was inversely correlated with total YP, suggesting that the â,å branch of lycopene cyclization is favoured over the â,â branch in high-YP genotypes. These results provide insights to the regulation of the carotenoid biosynthetic pathway during grain fill stage in durum wheat and will facilitate breeding for higher carotenoid concentration.

The thesis explores the canine oral cavity, namely, the teeth and the most common dental diseases. Dental injury and disease in dogs is a topic of growing interest in veterinary science. The theoretical section discusses the anatomy of the head, oral cavity and teeth. It presents general knowledge of veterinary dentistry and a list of the most common oral cavity diseases. The practical section explores the suitability and the effectiveness of two prevention methods against the build-up of dental plaque, respectively, against the spread of periodontitis. Diseases affecting the periodontium are increasingly common in dogs; they are deemed to be the most frequent diseases affecting small animals above five years of age. There are two most common periodontal diseases. The first, gingivitis, is a reversible inflammation of the gum. The second, periodontitis, is essentially irreversible without specialized treatment and often leads to loss of teeth. The major criterion for maintaining a healthy oral cavity is prevention. Therefore, two methods of home-based prevention are compared in the practical part of the thesis. First, all patients underwent a full-scale dental treatment in a veterinary centre, that is, a comprehensive ultrasonic cleaning and polishing with dental cleaning paste. Then, ascophyllum nodosum, a seaweed also known as Norwegian kelp, was mixed within the daily food ration of half of the patients. In this way, the teeth were being cleaned passively. The second half of the patients had their teeth cleaned with Orozyme, an enzyme-formula oral hygiene gel for dogs, and this way an active teeth cleaning method was explored. Six weeks after the initial dental treatment, a dental plaque identification test was carried out in a veterinary centre. Statistical analysis of the resulting data did not signal substantial differences between the treatment with Norwegian kelp and that of using the oral gel. A combination of the two techniques is, therefore, recommended as the best prevention strategy against plaque build-up.

Made available in DSpace on 2014-06-11T19:29:06Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-12-14Bitstream added on 2014-06-13T20:18:53Z : No. of bitstreams: 1 ceccato_da_me_sjrp.pdf: 1326355 bytes, checksum: e0343f52f9da425a55eecbf071f7b4ec (MD5) / O objetivo deste trabalho foi a investigação da potencialidade de sistemas luminescentes de matrizes à base de silicatos contendo Ba 2+ dopados com Eu 3+ , de serem aplicados na elaboração de eletrodos de pasta de carbono modificados (EPCM) para atuarem como sensores eletroquímicos. Para obtenção do material modificador do eletrodo foi desenvolvida uma rota de síntese sol-gel a qual tem como precursor o acetato de bário, Ba(CH3COO)2, o tetraetoxissilano, TEOS, como alcóxido para formação da cadeia polimérica e o ácido acético, CH3COOH, como solvente para dissolução do sal de bário, além de servir como catalisador da reação. Após a obtenção do material na sua forma gel e xerogel (aquecida a 100°C) essas formas foram caracterizadas por análise térmica, difração de raios X, espectroscopia no infravermelho e espectroscopia de luminescência. A partir dos resultados, verificou-se que quando o gel produzido é aquecido a 450°C e a 1100°C as fases formadas são o carbonato e silicato de bário, respectivamente. O material na sua fase silicato, aquecido a 1100°C, apresentou melhores propriedades luminescentes quando comparado ao material xerogel, sendo possível detectar na fase silicato um maior número de transições eletrônicas do európio. Conhecendo a estrutura do material em diferentes temperaturas ele foi utilizado para a elaboração de EPCMs, preparados a base de grafite e óleo mineral como aglutinante, no qual uma porcentagem do material modificador desenvolvido foi adicionada. Os modificadores testados foram os materiais na fase xerogel contendo 0,5, 1, 5 e 10% em mol de európio, além dos materiais calcinados a 450°C dopado com 1% de európio. Aquele que apresentou melhor resposta eletroquímica foi o xerogel da amostra dopada a 1% de európio e, a partir desse... / The aim of this study was to investigate the potential of luminescent systems, based on silicate matrices containing Ba 2+ and doped with Eu 3+ to be applied in the preparation of carbon paste electrode modified (CPEM) to act as electrochemical sensors. To obtain the modifier material of the electrode a sol-gel synthetic route was developed whereas it uses barium acetate, Ba(CH3COO)2 as precursor, tetraethoxysilane, TEOS as alkoxide to form the polymer chain and acetic acid, CH3COOH, as a solvent for dissolving the barium salt, as well as to act as a catalyst for the reaction. After obtaining the material in its gel and xerogel forms (heated to 100 ° C), they were characterized by thermal analysis, X-ray diffraction, infrared spectroscopy and luminescence spectroscopy. From the results, it was found that when the gel is heated to 450 ° C and 1100 ° C it is formed barium carbonate and silicate phases, respectively. The material in its silicate phase, heated to 1100 ° C, showed better luminescent properties when compared to the xerogel material and, exhibits a larger number of electronic transitions of europium. Knowing the structure of this material at different temperatures, it was used to prepare CPEMs, based on graphite and mineral oil as a binder, where a percentage of the modifier material developed was added. The modifiers were tested in phase xerogel materials containing 0.5, 1, 5 and 10% of europium, besides, the material calcined at 450 ° C doped with 1% of europium. The one that showed the best electrochemical response was the xerogel sample doped at 1% europium and from this modifier, different tests were carried out by using cyclic voltammetry to establish the best conditions, such as europium concentration and calcination temperature of the material modifier. Parameters such as pH and electrolyte... (Complete abstract click electronic access below)

Made available in DSpace on 2014-06-12T15:50:21Z (GMT). No. of bitstreams: 2 arquivo2709_1.pdf: 8987943 bytes, checksum: 1681d97cc5bb9ba5480a3f16109328b0 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2010 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / As argamassas e os concretos modificados por polímeros são comumente aplicados como materiais de reparo na construção civil. Porém, nem sempre as condições de desempenho desejadas são alcançadas. As propriedades físicas, mecânicas e de durabilidade destes materiais têm sido amplamente estudadas pela comunidade científica. As modificações microestruturais induzidas pelos polímeros nas pastas e sua relação com as propriedades macroestruturais, no entanto, ainda carecem de maior atenção por parte desta comunidade. Neste trabalho a influência das adições poliméricas na microestrutura, na morfologia e no desenvolvimento das principais fases cimentícias hidratadas, principalmente relativas as fase C-S-H e aluminatos, em diferentes idades (1, 3 e 28 dias) e condições de cura (úmida e mista), foi analisada sob ponto de vista microestrutural. Também se procurou correlacionar as características microestruturais das pastas com as propriedades mecânicas. As pastas estudadas foram classificadas por: pasta de referência (REF), pastas modificadas por uma emulsão a base de um polímero acrílico (PE) (pasta E) e pastas modificadas por uma emulsão a base de um copolímero acrílico-estireno (PAe) (pasta A). Os teores de polímeros de 5%, 15% e 25%, adicionados em relação à massa do cimento, foram utilizados nas pastas modificadas. A relação a/c adotada foi 0,35. O método utilizado para avaliação das pastas no estado fresco foi à análise dos tempos de pega. No estado endurecido várias análises microestruturais como: termogravimetria e derivada da termogravimétrica (TGA/DTG), espectroscopia de infravermelho por transformada de Fourier (FTIR), difratometria de raios-X (DRX), microscopia eletrônica de varredura (MEV) e espectroscopia de ressonância magnética nuclear no estado sólido de 29Si e 27Al (RMN) foram realizadas. Para análise macroestrutural foram adotados os ensaios de resistência à compressão, resistência à tração por compressão diametral e absorção de água por capilaridade. A análise dos resultados mostrou que ambos os polímeros influenciaram a cinética de hidratação do cimento, a microestrutura das pastas e as características de cristalinidade das fases hidratadas. Sendo esta influência mais perceptível quando teores de 15% e 25% dos polímeros (PAe e PE) foram adicionados às pastas. Os resultados mecânicos e de durabilidade estudados comprovaram que o pior desempenho das pastas produzidas com o polímero PAe (pastas A) foi decorrente do menor amadurecimento destas pastas, modificação da estrutura da fase C-S-H e provavelmente devido a maior porosidade e interconexão dos poros. Em ambas as pastas, o retardo dos produtos hidratados foi facilitado pelo envolvimento das partículas poliméricas e/ou filmes ao redor dos grãos anidros que dificultaram a dissolução dos mesmos e precipitação dos hidratos cimentícios. A interação química entre o compósito não foi tão evidente nas pastas estudadas, sendo, portanto, a interação física a principal causa dos retardos apresentados. A formação de produtos cristalinos menores e sem orientação preferencial observados na pasta E, juntamente à melhor qualidade e estabilidade do filme polimérico do polímero acrílico, no meio alcalino da pasta cimentícia, também contribuiu para o melhor desempenho quanto à resistência à tração e compressão destas pastas em relação às pastas A. Por RMN foi possível constatar menores quantidades da fase C-S-H e de sítios Q1 e maiores quantidades de sítios Q2 das pastas modificadas, bem como diferenças no comprimento médio das cadeias de silicato. Estes fatores podem ter contribuído para a maior resistência a compressão da pasta REF, no mínimo 55% superior à resistência das pastas modificadas, conforme o tipo e a relação p/c adotada. Nas pastas A e E (15% e 25%) foram observadas grandes quantidades de fases carbonáticas do tipo carboaluminato, principalmente aos 28 dias. A condição de cura influenciou de maneira diferenciada para a formação das fases hidratadas CH, C-S-H e fases carbonática. Quanto a influência da cura nas propriedades mecânicas estudadas, a constatação mais evidente foi observada na pasta REF que apresentou o melhor desempenho quando submetida à condição de cura úmida

Thesis: M.S., Massachusetts Institute of Technology, Department of Nutrition and Food Science, 1979 / Bibliography: leaves 95-99. / by Herman Hiu-Lam Sze. / M.S. / M.S. Massachusetts Institute of Technology, Department of Nutrition and Food Science

Durum wheat (Triticum durum Desf.) is produced primarily in the Northern Great Plains and the Pacific Southwest of the United States. Current germplasm is predominantly of the spring growth habit. The objective of this study was to determine the feasibility of winter durum production in Virginia based upon both yield and quality parameters. Adaptation and yield potential of available winter durum lines were assessed from 1993-1998, in three physiographic regions in Virginia. The highest average durum yields were produced in the northern piedmont plateau at the Orange County location. Winter durum yields generally averaged 1600-2800 kg/ha less than soft red winter wheat, traditionally grown in the state. The price premium for high quality durum can compensate for this difference in yield. Based on average durum yields, and assuming the grain meets U.S. No. 2 Hard Amber Durum standards, durum production in Virginia would have been more profitable than soft red winter wheat production in 1994 and 1997. Physical and chemical quality analyses of the top 19 performing durum lines were performed to determine grain marketability, suitability for pasta, and potential consumer acceptance of the end product. Protein content and gluten strength of the Virginia grown durum were acceptable. Color, firmness, and cooking loss of pasta produced from Virginia grown durum were comparable to pasta produced from commercial semolina. Requirements for U.S. No. 2 Amber Durum were met by 21% of the lines in both 1996 and 1997. Overall, the wet, humid Virginia climate was the greatest hindrance to durum production and quality. The field trials and quality analyses showed that high quality durum production in Virginia is possible, but not consistent over all years. / Master of Science

El objetivo general de la presente tesis fue el diseño y la construcción de un biosensor amperométrico para determinar glucosa en jugos de fruta (utilizando el de manzana como modelo) que sea económico, de fácil construcción y que tenga respuesta rápida. Con tal fin se construyó un electrodo de pasta de carbono que consistió en un cilindro de teflón con un contacto eléctrico de acero inoxidable. Los materiales de la pasta de carbono fueron una mezcla de polvo fino de grafito y parafina, a los cuales se agregó la enzima glucosa oxidasa (GOx) y el ferroceno, como mediador. Se estudiaron diferentes condiciones de operación del biosensor tales como el pH del medio de reacción, el potencial aplicado y la carga de enzima en la pasta de carbono, siendo las condiciones óptimas seleccionadas: medio de reacción (buffer de fosfatos pH 7), potencial de trabajo (0.16 V) y carga enzimática (10%). Se determinó la actividad enzimática de la enzima tanto libre como luego del proceso de inmovilización, y se estudió la cinética de la enzima en el electrodo, la cual se corresponde con la cinética típica de Michaelis-Menten, siendo los valores de los parámetros cinéticos k’m= 0.0195 M e imax= 35.5 μA. A continuación se construyó la curva de calibración cuyo intervalo lineal de concentraciones de glucosa fue de 0.1 mM a 4.48 mM, con una sensibilidad de 0.61 μA/mM y un valor del límite de detección de 0.05 mM, valores completamente aceptables para el biosensor en cuestión. También se evaluaron características del sensor como su tiempo de respuesta, que fue menor a 12 segundos en todos los casos y la repetibilidad y la precisión intermedia dando en ambos casos muy buenos resultados. Posteriormente se evaluó la estabilidad del sensor bajo diferentes condiciones de almacenamiento con y sin inmersión en la solución buffer y tanto bajo refrigeración como a temperatura ambiente. Todos los resultados fueron altamente satisfactorios y concuerdan con los esperados para el biosensor y más aún teniendo en cuenta la simpleza respecto de los materiales empleados y a la construcción del mismo. Otro estudio fue la evaluación de las interferencias debidas a sustancias electroquímicamente activas en el jugo de fruta, en este caso de manzana, que puedan afectar a la señal de la glucosa. Como posibles interferentes se estudiaron: ácido ascórbico, sacarosa, fructosa, almidón, ácido málico y ácido cítrico. Sólo el ácido ascórbico fue una sustancia interferente, debiendo eliminarse este compuesto del jugo como paso previo a la determinación de glucosa con el biosensor. Se estudiaron dos técnicas de eliminación: eliminación enzimática del ácido ascórbico y eliminación por oxidación directa con oxígeno del aire ambiente. Ambas técnicas dieron excelentes resultados en la eliminación de este compuesto. Finalmente se procedió a la determinación de glucosa en muestras reales, para lo cual se emplearon dos jugos de manzana: uno comercial y uno concentrado obtenido directamente de fábrica. Para validar los resultados obtenidos con el biosensor se utilizó un glucómetro digital. En todos los casos los errores en las determinaciones respecto a los valores obtenidos con el glucómetro fueron menores al 4%, lo que indica el muy buen desempeño del biosensor. / The main objective of the present Thesis was the design and construction of an amperometric biosensor to determine glucose in fruit juices (using apple juice as a model), considering this type of bio-electrodes are relatively cheap, simple to develop, set up and run and characterized by a fast response. The used carbon paste electrode consisted in a Teflon cylinder with stainless steel electric contact. Carbon paste was a mixture of graphite in fine powder and liquid paraffin, to which the enzyme glucose oxidase (GOx) and ferrocene as mediator was added. Several operation conditions were studied such as reaction medium pH, working potential and enzymatic load in the carbon paste, being the optimal conditions selected phosphate buffer (pH 7) as reaction medium, a working potential of 0.16 V, and 10% enzymatic load. Enzymatic activity of both free enzyme and enzyme after the immobilization process was determined. Furthermore the kinetic of the enzyme in the electrode was studied, and the result shows that it follows a typical Michaelis-Menten kinetic, with k’m= 0.0195 M and imax= 35.5 μA. The calibration curve shown that the linear range of glucose concentration was in the range 0.1 mM to 4.48 mM, with a sensitivity of 0.61 μA/mM and a detection limit of 0.05 mM. These values are completely acceptable for this kind of biosensor. Sensor characteristics, including response time (<12 sec. in all cases), intermediate precision and repeatability were evaluated. Stability of the sensor under different storage conditions was also evaluated. Results were highly satisfactory and consistent, considering used materials and simplicity of construction. Interferences from electrochemically-active substances in apple juice, which may affect glucose signal, were carefully considered. The possible studied interfering substances were: ascorbic acid, sucrose, fructose, starch, malic acid and citric acid. Only the ascorbic acid was observed to be an interfering substance, which must be removed from juice previously to the determination of glucose with the biosensor. Two removal techniques for ascorbic acid were assayed: enzymatic removal and elimination by direct oxidation with air. Both techniques showed to be appropriate for ascorbic acid elimination. Finally, the determination of glucose in real samples was carried out, using two apple juices samples, a ready to drink commercial one, and a concentrated juice directly obtained from a factory. To validate the results obtained with the biosensor a digital glucometer was used. In all cases the errors in the determinations were lower than 4%, demonstrating the very good performance of the biosensor.

Les réactions de phosphorylation / déphosphorylation chez les bactéries régulent plusieurs fonctions cellulaires telles que croissance, différenciation, pathogénie, résistance aux antibiotiques, réponse au stress, formation des biofilms ainsi que plusieurs processus impliqués dans le métabolisme secondaire. Cependant, les signaux qui déclenchent la cascade de signalisation par phosphorylation/déphosphorylation intracellulaire restent encore peu connus. Staphylococcus aureus est une bactérie à Gram-positif pathogène pour l‟homme. Elle est l‟une des principales causes des infections nosocomiales et ce pathogène opportuniste est capable de provoquer de multiples infections allant du furoncle à la septicémie. Nos études se sont basées sur la caractérisation aux niveaux structural et fonctionnel de deux protéines de cette bactérie : une sérine/thréonine kinase nommée Stk1 ainsi que l‟un de ses substrats, la triose phosphate isomérase. Stk1 a déjà été identifiée comme responsable de la phosphorylation de plusieurs enzymes impliquées dans le métabolisme central de la bactérie ainsi que dans les phénomènes de virulence et de résistance à l‟antibiotique phosphomycine. Cependant, à ce jour, aucune caractérisation structurale n‟a été conduite sur cette kinase. Nous avons ainsi mené une étude cristallographique de plusieurs domaines de cette protéine et nous présentons, plus particulièrement, la structure de trois domaines extracellulaires dits « PASTA », ainsi qu‟un modèle tridimensionnel de la protéine entière. Les domaines PASTA sont spécifiques des Ser/Thr kinases et des Penicillin-Binding Proteins et sont impliqués dans la synthèse du peptidoglycane. Par conséquent, la connaissance de la structure de ces domaines chez Stk1 pourrait servir de base à la conception rationnelle de nouveaux inhibiteurs à visée thérapeutique. Enfin, nous avons démontré que l‟activité de l‟un des substrats de Stk1, la triose phosphate isomérase, était régulée par phosphorylation / déphosphorylation, et nous avons décrit le mécanisme qui contrôle son activation/inactivation réversible. / The phosphorylation /dephosphorylation reactions in bacteria regulate various cellular functions such as growth, differentiation, pathogenicity, antibiotic resistance, stress response, biofilm formation as well as several processes involved in secondary metabolism. However, detailed understanding of their complete signaling pathways induced by phosphorylation/dephosphorylation is still unclear. Staphylococcus aureus is a Gram-positive bacterium and a human pathogen. It is one of the primary causes of nosocomial infections and this opportunist pathogen is able to cause multiple infections ranging from furuncle to septicemia. This study is focused on the structural and functional characterizations of two proteins from this bacterium: the serine/threonine kinase Stk1 and one of its substrates, the triose phosphate isomerase. Stk1 has been previously identified as responsible for the phosphorylation of several enzymes involved in the central metabolism of this bacterium as well as virulence and resistance to the antibiotic phosphomycin. However, no structural characterization has been done to date. We have performed a crystallographic study of several domains of this protein. We now present the structure of three extracellular domains designated “PASTA” in addition to the 3D molecular model of the entire protein. PASTA domains are specific to bacterial Ser/Thr kinases and to Penicillin-Binding Proteins which are involved in the peptidoglycan synthesis. Thus, the structural knowledge of PASTA domains from Stk1 could be of particular interest in the rational drug-design of new inhibitors with therapeutic aims. Finally, we have demonstrated that triose phosphate isomerase activity is regulated by phosphorylation/dephosphorylation and we have described the reversible activation/inactivation mechanism.

Call number: LD2668 .T4 1984 J32 / Master of Science