No description available.

No description available.

No description available.

Flagellate protozoa from the order Trypanosomatida have developed a range of strategies to survive in their mammalian hosts. A consequence is that the glycolytic pathway has assumed an important role, especially in bloodstream-form Trypanosoma brucei, where it is essential as the sole producer of ATP. The seventh enzyme in the pathway, 2,3-bisphosphoglycerate-independent phosphoglycerate mutase (iPGAM) is particularly attractive as a drug target because it shares no common properties with the corresponding enzyme in humans. This enzyme catalyses the conversion of 3PGA to 2PGA, with the requirement for metal ions to assist the catalytic function. In this study, two important biochemical and structural aspects of the enzyme were investigated: i) The in vitro and in vivo requirements for biologically relevant metal ions to support the activity of iPGAM, and ii) The ability of trypanosomatid iPGAM to exist in multiple conformations and oligomeric states in solution. The maximum activity of iPGAM in vitro requires Co2+, but this cannot be the case in vivo where ICP-OES analyses confirmed that Co2+ was essentially undetectable in T. brucei cytosolic fractions. The activity of iPGAM in vivo is therefore one of the lowest among the glycolytic enzymes. By contrast, Mg2+ and Zn2+ were found to be the most abundant metals in both cytosolic fractions and in purified bacterially expressed iPGAM. Our newly-developed multimode-plate reader discontinuous assay further revealed that of the biologically relevant metals, only Mg2+ can support iPGAM activity, but at less than 50% of the level of Co2+. By contrast, Zn2+ strongly inhibits iPGAM. This assay which was developed with minimal metal interference on the coupling enzymes, also showed that in solution, the ratio of the concentrations of 3PGA:2PGA (substrate:product) at equilibrium is not 1:1 as observed in the crystal structure, but is in fact 12:1, which may be due to the tighter binding of 2PGA to the enzyme. A series of biophysical analyses, notably by SEC-MALS showed that iPGAM from Leishmania mexicana, another trypanosomatid protozoan parasite exists in different forms and oligomeric states in solution, either as the closed-form monomer, openiii form monomer, or closed/open-form dimer which can be successfully separated by ion-exchange chromatography. The open-form LmiPGAM is particularly relevant for drug development, as the catalytic site in the closed-form structure is poorly inaccessible. Both virtual and high-throughput screening approaches were used to identify novel potential inhibitors. Out of a collection of 11 compounds tested at 1 mM, two showed substantial inhibition with 49% and 14% remaining activity. Taken together, the findings from this study demonstrated the potential of iPGAM to be a key modulator in controlling glycolytic flux in trypanosomes, and thus further validated it as an important drug target.

The purpose of this study, therefore, was threefold in nature: (1) to determine the effects of x-irradiation on the influx and efflux of potassium in compound nerve fibers (2) to attempt to relate the radiation-induced changes in electrical activity with potassium flux and (3) to use the information obtained to gain insight into the possible cellular site (s) of radiation insult to compound nerves.

Nitrous oxide (N2O) is a potent greenhouse gas (GHG) which is released naturally into the atmosphere as a by-product of the microbial processes of nitrification and denitrification. Agricultural activities are believed to account for up to 80% of anthropogenic N2O emissions at a global scale; however, these estimates are prone to large uncertainties due to the large temporal and spatial variability associated with flux measurements. This thesis contains five studies which aimed to improve the ability to measure and predict N2O emissions from agricultural activities. A closed loop dynamic chamber was developed using a quantum cascade laser (QCL). This method provided high precision chamber measurements of N2O flux from soils with a detection limit below 4 μg N2O-N m-2 h-1. Using the dynamic chamber method allowed for a detailed investigation of uncertainties in individual measurements including contributions from regression fitting, temperature and pressure. The lack of negative fluxes measured that were outwith the detection limits of the methodology (0.3% of all measurements) highlighted that the uptake of N2O reported in some previous literature is likely to have been the result of detection limits of measurement methods applied. Spatial variability of N2O flux was investigated at the plot, field and farm scale. Fluxes were measured from a grassland field plot before and after a tillage event. These measurements highlighted the large spatially variability present in N2O fluxes from agricultural soils. Fluxes varied by up to three orders of magnitude over distances less than 5 metres after the tillage event. A field scale experiment carried out on grazed grassland investigated relationships between soil properties and N2O flux. This study found that N2O emissions correlated strongly with available nitrogen content in the soil and that animal waste was likely responsible for the spatial variability of N2O flux observed at the field scale. A farm scale inventory of N2O emissions was carried out investigating several large point sources of N2O and emissions from the wider field coverage. The inventory estimates that nitrogen fertiliser application is the single largest N2O source from the livestock farm accounting for 49% of annual emissions.

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

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

L'accroissement des performances énergétiques de systèmes industriels motorisés mettant en œuvre des machines électriques à courants alternatifs fait actuellement l'objet d'enjeux majeurs. Les travaux présentés dans ce mémoire s'inscrivent dans ce contexte et concernent la conception d'un outil (cellule) de diagnostic énergétique. Le verrou majeur à lever consiste à estimer le couple électromagnétique des machines AC, sans décapoter leurs boîtes à bornes ni mesurer leurs vitesses de rotation. La thèse a permis de développer des techniques non invasives, basées sur la mesure du courant de ligne et/ou du flux de dispersion dans l'environnement proche de la machine. Des analyses fines de la distribution du flux de dispersion autour de la carcasse ont été réalisées car le flux est atténué et déphasé sous l'influence des courants de Foucault. L'analyse a également permis de distinguer la contribution des conducteurs actifs de celle des têtes de bobines dans la génération du flux externe. Une image du flux d'entrefer a donc pu être mise en évidence, ainsi que la manière de la mesurer, conduisant à la définition de protocoles de détermination du couple. Ces derniers sont complétés par une méthode reposant sur la mesure ou l'estimation à partir du flux de dispersion du courant de phase. Les méthodes dégagées ont été appliquées à des machines asynchrones dont les puissances s'échelonnent de 3 à 200 kW. La conception de la cellule s'est étendue à son architecture et, notamment, à la transmission sans fil des informations collectées. La gestion de l'autonomie a été un critère prépondérant durant toute l'étude, conduisant d'une part à l'élaboration d'algorithmes légers donc peu énergivores pour la cellule et, d'autre part, à l'introduction du flux de dispersion comme source d'énergie alternative. / The energetic performance increase of industrial processes using AC electrical rotating machines is nowadays of great concern. The developments presented in this thesis are situated in this context and are about the design of an energy monitoring tool (cell). The main scientific barrier to lift is the estimation of the electromagnetic torque of AC machines without dismounting their terminal box or measuring their shaft speed. Non invasive methods have been developed; they are based on the measurement of the phase current and/or the external flux in the immediate vicinity of the machine. Analyses of the external flux distribution around the external housing were made : the magnetic flux is attenuated and phase shifted because of the eddy current effect. Then, the analysis has made it possible to distinguish the contribution of the wires placed in the slots from the effect of the end-windings in the external flux emission. The work explains how to determine an image of the external flux, as well as the way to measure it. That leads to the definition of protocols for determining the electromagnetic torque, which, for some of them use current measurements or its estimation from the external flux. The proposed methods have been applied to induction machines with rated powers between 3 to 200 kW. The cell structure is described, in particular the wireless transmission of the measured information. The autonomy of the cell is a factor taken into account troughout the study, leading to the development of little-intensive computing algorithms. It is also shown that the external flux can be used as an additional energy source.

The effect of environmental conditions upon the growth, production and development of river phytoplankton was investigated for the feeder rivers to the Humber Estuary. The study was part of the Land Ocean Interaction Study LOIS) and focused upon the Rivers Trent and Yorkshire Ouse. The influence of physical, chemical and biological factors upon phytoplankton development were measured through routine fieldwork and laboratory analyses. During fieldwork measurements were collected which complemented measurements collected by LOIS colleagues. Data collected in this study included phytoplankton species composition, density and biomass and is situ rates of growth and production. In situ rates of loss through grazing and respiration were also measured. Laboratory investigations concentrated upon the effects of Ught and temperature upon dominant phytoplankton species and were developed to complement fieldwork. The project focused around four main aims. These were basically to assess the size and composition of phytoplankton maxima in the Trent and Ouse, measure in situ rates of growth and production, estimate losses from grazing and to develop models, using the data collected to assess the effect of environmental conditions upon phytoplankton development and autochthonous carbon in the Humber Estuary. The results showed that phytoplankton dynamics in the Trent and Ouse were controlled primarily by discharge, light and temperature. During spring, when conditions were favourable for growth, rapid phytoplankton growth and maximum rates of production were observed. However, spring floods often interrupted die large phytoplankton populations which developed. Other factors such as grazing and sedimentation were also considered as potentially important in the loss of phytoplankton. The turbid nature of the rivers resulted in a fine balance between photosynflietic gain and respirational loss. This temporal change in environmental conditions resulted in a temporal waxing and waning of the phytoplankton. This in turn had an impact upon the seasonality of the flux of autochthonous carbon to the Humber Estuary. Laboratory investigations and development of a photosynthetic model confirmed the importance of light and temperature upon phytoplankton development in these rivers. In terms of phytoplankton growth and production and the flux of autochthonous carbon, the Trent and Ouse were found to be typical of many other European rivers. The study highlighted the importance of the Trent as a source of autochthonous carbon to the Humber Estuary.