Vitamin D is hydroxylated to form several active metabolites, of these, 1,25- dihydroxyvitamin D3 [1,25(OH)2D3] is the most studied stimulatory product. It is now accepted that 1,25(OH)2D3 mediates its rapid actions on the control of phosphate homeostasis through its membrane receptor 1,25D3-MARRS (membrane associated rapid response steroid binding) protein. Another metabolite, 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] has been reported to be inhibitory with respect to calcium and phosphate absorption in intestine. Previous work in this laboratory has indicated that 24,25(OH)2D3 inhibits phosphate uptake in isolated intestinal cells and perfused duodenal loops and in vivo. This thesis further tested the hypothesis that the actions of 24,25(OH)2D3 on phosphate homeostasis are physiologically important. Catalase has been identified as a binding protein for 24,25(OH)2D3. We determined the localization of catalase in the presence and absence of steroid, monitored catalase mRNA levels related to gene 24,25(OH)2D3 gene transcription regulation. We studied the effects of the two isomers of 24,25(OH)2D3 on localization of catalase in chicken enterocytes over a time course of 15 sec to 60 min. It was demonstrated that 24R,25(OH)2D3 is the effective metabolite for catalase redistribution in vitro. We also studied the effects of vitamin D on catalase and phosphate uptake in chicken intestinal cells. It was once again demonstrated that 24R,25(OH)2D3 is the effective metabolite for decreasing phosphate uptake and catalase gene expression. These combined results lead us to conclude that 24,25(OH)2D3 is an important hormone in phosphate homeostasis in chick intestinal epithelial cells.

In order to understand the mineralogical association and distribution of arsenic (As) in the Hawthorn Group in central Florida, I examined in detail the chemical and mineralogical composition of 361 samples that were collected from 16 cores. Geochemical analyses were performed by hydride generation - atomic fluorescence spectrometry (HG-AFS) and inductively coupled plasma optical emission spectrometry (ICP-OES). The identification of discrete minerals was aided by scanning electron microscopy (SEM) and chemical compositions were obtained by electron-probe microanalyses (EMPA). Arsenic concentrations for all Hawthorn samples vary from 0.1 to 69.0 ppm with a mean of 5.6 ppm. Average As concentrations for the individual units of the Hawthorn Group vary significantly from 9.0 ppm in the Peace River Formation to 3.0 ppm in the Tampa Member of the Arcadia Formation. This detailed mineralogical and geochemical study demonstrates that: (1) Arsenic in the Hawthorn Group varies from the formation to formation and is primarily concentrated in trace minerals, such as pyrite; (2) Concentrations of arsenic in pyrite crystals can vary drastically from a minimum of 0 ppm to a maximum of 8260 ppm; (3) Pyrite occurs in framboidal and euhedral forms and is unevenly distributed throughout the Hawthorn Group; (4) Hydrous ferric oxides can contain up to 540 ppm of arsenic; (5) Phosphate and organic material, and clays contain lower arsenic concentrations that pyrite and hydrous ferric oxides; and (6) Arsenic, sulfur, and iron have lognormal distribution throughout the Hawthorn Group. This study is important because phosphorous, arsenic and sulfur are chemically closely related, and thus they co-occur posing a potential problem for the phosphate industry. Information about the concentration, distribution and mineralogical association of naturally occurring arsenic is essential to forecast its behavior during anthropogenically induced physico-chemical changes in the aquifer. Recently, aquifer storage and recovery (ASR) facilities in west-central Florida reported arsenic concentrations in excess of 100 micro g/L (100 ppb) in recovered water. The ASR storage zone in this area is in the Suwannee Limestone, which directly underlies the Hawthorn sediments. It is crucial to the future of ASR in this area to understand the source, distribution, and cycling of arsenic in the overlying Hawthorn Group and the Florida Platform.

The Hillsborough River flows southwesterly through Pasco and Hillsborough counties in west central Florida. From its source at the Green Swamp to its mouth in Hillsborough Bay, the river is joined by many tributaries and man-made inputs. Spatial and temporal variations in the river's major ion and CO2 system chemistry were examined in a two-year study between 1999 and 2001. At thirteen sampling stations along approximately 54 miles of the river, water samples were collected in surroundings that ranged from pristine to urban. Samples were collected monthly for the first year and periodically thereafter. Concentrations of major ions were lowest in the river's headwaters, showed only minor spatial variations in mid-river, and sharply increased in tidally influenced waters below a dam on the lower river. A major tributary, Blackwater Creek, exerts a strong influence on the river's phosphate concentrations, and Crystal Springs, upstream of Blackwater Creek, exerts a strong influence on nitrate concentrations in the river. Downstream of Crystal springs, NO3- concentrations decreased steadily to levels that are more than an order of magnitude lower than levels in the upper river. Temporal ion concentration variations can be quite large. Low major ion concentrations were observed in the rainy season (June-September), while phosphate concentrations increased dramatically during extremely wet conditions. Seasonal variations were also observed in the river's CO2 system. Riverwater pH decreased during periods of high precipitation along with CaCO3 saturation state. CaCO3 supersaturation was observed during the exceptionally dry periods of the study, and undersaturation was observed during periods of high rainfall.Overall, the chemistry of the Hillsborough River is greatly influenced by temporal and spatial variations in the river's tributaries, groundwater sources, and anthropogenic inputs.

Under hösten 1994 startades en undersökningsserie av Stockholm Vatten AB där bl.a. syrgastäring och PO4-P-läckage av sediment analyserades från ett antal sjöar i Stockholms tillrinningsområde. Som ett led i undersökningsserien analyserades i denna rapport syrgastäringshastigheten och PO4-P-läckaget av homogeniserat sediment vid 13 provpunkter i Stockholms innerskärgård under våren 1995 med hjälp av en ny analysapparatur. Samtidigt undersöktes analysapparaturens reproducerbarhet, biomassa av bakterier samt potentiell aktivitet hos denitrifierande bakterier i sediment från respektive provpunkt. Resultaten tyder på att syrgastäringshastigheten beror på från vilken bottentyp sedimentet är hämtat samt den organiska halten hos sedimentet. Likaså verkar storleken på PO4-P-läckaget från sedimenten bero på från vilken bottentyp sedimentet är hämtat men även på de fysikaliska betingelserna som karaktäriserar provpunkten. Reproducerbarheten hos den nya analysapparaturen kan anses vara relativt god vid beräkning av både O2- och PO4-P-koncentrationen i vattenpelaren ovanför sedimentytan. Vid koncentrationer hos syrgasmättnaden, där bl.a. syrgastäringshastigheten har beräknats, är variationskoefficenten låg, dvs. för koncentrationer ≥50 %. På liknande sätt är variationskoefficienten låg vid PO4-P-koncentrationer över 100 µg/l. Biomassan av bakterier varierade mellan 0,48 och 2,66 mg/g TS med de lägsta halterna längst in i provtagningsområdet och de högsta längst ut i området. Den potentiella aktiviteten hos denitrifierande bakterier uppvisade ett oregelbundet resultatmönster i undersökningsområdet. / During autumn 1994 an investigation-sequence was started by Stockholm Vatten AB where oxygen demand and PO4-P-leakage were analysed of sediments from few lakes in the drainage area of Stockholm. As a contribution to the investigation-sequence the oxygen demand and the PO4-P-leakage of homogenised sediments at 13 locations in the archipelago of Stockholm were analysed during spring 1995 in this report, using a new method. Parallel to these analyses there was a test of the reproducibility of the analysis-device, determination of bacterial biomass and potential activity of denitrified bacteria in sediments from each sample location. The results indicate that the oxygen demand is dependent on type of the bottom the sample were taken and on the organic content of the sediments. The magnitude of the PO4-P-leakage seems also to be dependent on the type of the bottom as well as the physical conditions that characterise the location. The reproducibility of the new analysis-device seems to be relatively good for measurements of both O2- and PO4-P-concentrations in water above the sediments. The coefficient of variation was low at O2-saturation where the oxygen demand were measured, i.e. O2-saturation ≥50%. In the same manner, the coefficient of variation was low at PO4-P-concentrations above 100 µg/l. The bacterial biomass varied between 0,48 and 2,66 mg/g DS, with the lowest concentrations in the inner parts of the test-area and the highest concentrations in the outer. The result of the potential activity of denitrified bacteria showed an irregular pattern in the test-area.

Ce travail vise à étudier l’hydratation et les propriétés des ciments brushitiques à base de wollastonite dans la perspective d’une application au traitement et au conditionnement de déchets radioactifs de faible ou moyenne activité acides et/ou contaminés en strontium. Une étude des processus conduisant à la prise et au durcissement d’un ciment commercial est d’abord menée. L’influence de la composition de la solution de gâchage sur les réactions mises en jeu est ensuite précisée. Enfin, une première évaluation du potentiel de ce matériau pour la décontamination ou l’immobilisation d’effluents aqueux contaminés en strontium est réalisée.Les pâtes de ciment brushitique à base de wollastonite sont préparées à partir de wollastonite broyée et d’une solution d’acide phosphorique concentrée contenant des cations métalliques (Zn2+ et Al3+) ainsi que du borax. La wollastonite réagit selon un processus de dissolution/précipitation qui conduit à la formation de brushite, de silice amorphe et d’un aluminophosphate de calcium et de zinc amorphe dont la structure a été caractérisée par RMN-MAS du 31P et 27Al. La précipitation de brushite est précédée par la formation transitoire de phosphate monocalcique monohydraté. La simulation thermodynamique à l’aide d’un code de spéciation géochimique de la réaction de la wollastonite avec une solution d’acide phosphorique reproduit bien la séquence de précipitation des phases cristallines observée expérimentalement.Il apparaît que la concentration optimale de l’acide phosphorique dans la solution de gâchage est comprise entre 9 et 10 mol.L-1. Le bore retarde la prise du ciment tandis que le zinc l’accélère. L’ajout d’aluminium, qui permet la précipitation massive d’aluminophosphate de calcium amorphe, s’avère nécessaire pour obtenir un matériau avec de bonnes performances mécaniques. Une étude de surfaces de réponses par plan d’expériences, suivie d’une optimisation multicritères, a permis d’identifier un domaine de compositions de solutions de gâchage conduisant à un matériau possédant les propriétés recherchées (en terme de temps de prise, auto-échauffement et résistance mécanique) pour une matrice de conditionnement de déchets.Une étude cristallographique montre par ailleurs que la brushite peut incorporer au moins 30 % (mol/mol) de strontium en substitution du calcium dans sa structure. Des essais de piégeage du strontium par une pâte de ciment broyée, menés en suspension diluée, conduisent à une isotherme de sorption de type S, témoignant de l’existence de plusieurs mécanismes de rétention. Enfin, un essai de lixiviation sur un monolithe contenant du strontium révèle le bon confinement de ce dernier, avec un coefficient de rétention Rd plus de 100 fois supérieur à celui obtenu avec une pâte de ciment Portland. / This work aims at studying the hydration process and the properties of wollastonite-based brushite cements. These binders may indeed offer new prospects for the treatment or conditioning of low- or intermediate- level radioactive wastes characterized by a strong acidity and/or a contamination by strontium. First, a study of the hydration process is carried out with a commercial cement. Then, the influence of the mixing solution composition on the setting and hardening process is determined. Finally, a first assessment of the potential of this material for the decontamination and immobilization of strontium-containing aqueous effluents is performed.Wollastonite-based brushite cement pastes are prepared by mixing ground wollastonite and a phosphoric acid solution containing metallic cations (Al3+ and Zn2+) and borax. Wollastonite reacts through a dissolution/precipitation process, which leads to the formation of brushite, amorphous silica and amorphous zinc and calcium aluminophosphate whose structure has been investigated by 31P and 27Al MAS-NMR. The brushite precipitation is preceded by the transient formation of monophosphate calcium monohydrate. The thermodynamic simulation of the wollastonite reaction with a phosphoric acid solution, using a geochemical speciation code, fairly well reproduces the precipitation sequence of crystalline phases observed experimentally.It appears that the optimum phosphoric acid concentration in the mixing solution is comprised between 9 and 10 mol.L-1. Boron retards the cement setting whereas zinc accelerates it. The addition of aluminium, which leads to the massive precipitation of amorphous calcium aluminophosphate, is proved to be necessary to obtain a material with high mechanical strength. Thanks to response surface methodology and multi-criteria optimization, a composition domain of the mixing solution is pointed out, leading to a material with good properties (in terms of setting time, self-heating and mechanical strength) for waste conditioning.A crystallographic study also shows that brushite is able to incorporate at least 30 % (mol/mol) of strontium in substitution for calcium in its structure. Strontium retention tests by a ground cement paste in diluted suspension lead to a type S sorption isotherm, meaning that several retention mechanisms are involved. Finally, a leaching experiment performed on a cement monolith containing strontium shows that this species is well confined within the cement matrix, with a retention coefficient at least two orders of magnitude higher than that of a Portland cement paste.

5-Aminolevulinate synthase (ALAS) and 8-amino-7-oxononanoate synthase (AONS) are two of four homodimeric members of the alpha-oxoamine synthase family of pyridoxal 5'-phosphate (PLP)-dependent enzymes. The evolutionary relationships among α-oxoamine synthases representing a broad taxonomic and phylogenetic spectrum have been examined to help identify residues that may regulate substrate specificity. The structural plasticity of ALAS has been documented in studies of functional circularly permuted ALAS variants and the single polypeptide chain ALAS dimer (ALAS/ALAS) exhibiting a greater turnover number than wild-type ALAS. An examination of the contribution of each ALAS/ALAS active site to the enzymatic activity shows that each active site makes distinct contributions to the steady-state activity of the enzyme. Chimeric ALAS/AONS proteins exhibited an oligomeric structure with two sites having ALAS activity and two sites having AONS activity. Remarkably, the steady-state rates for both the ALAS and AONS activities were lower than that observed in the parent enzymes, while the reactivity of the ALAS sites in ALAS/AONS was similar to that of wild-type ALAS. We propose that the different contribution of each active site to the steady-state activity of ALAS/ALAS and the reduced steady-state activities of the ALAS/AONS chimera, compared to the parent enzymes, relate to different extents of conformational changes associated with product release due to the strain caused with the linking the two ALAS (or ALAS and AONS) subunits. Thus, the extensive plasticity seen in ALAS extends to another member of the α-oxoamine family, AONS. In the α-oxoamine synthase family a conserved histidine hydrogen bonds with the phenolic oxygen of PLP and may be significant for substrate-binding, PLP-positioning, and maintaining the pKa of the imine nitrogen. The replacement of this conserved histidine, H282, with alanine in murine erythroid ALAS has multiple effects on the spectral, binding, and kinetic properties of the enzyme and supports the conclusion that H282 plays multiple roles in the enzymology of ALAS. Altogether, these results imply that amino acid H282 coordinates the movement of the pyridine ring with the reorganization of the active-site hydrogen bond network and acts as a hydrogen bond donor to the phenolic oxygen to maintain the protonated Schiff base and enhance the electron sink function of the PLP cofactor.

A sequential extraction method was used to determine which dominant sedimentary mineral phase was involved in phosphorus retention in the sediments of Lake Rotorua and to verify the importance of iron phases in the role as a phosphorus sink. The observed influence of the experimental conditions upon the extent of phosphate adsorption to various iron phases shows a considerable quantity of phosphorus is present in the reducible phase and in the residual mineral phase. The phosphorus associated with iron(III) oxide phases was released into solution under reducing conditions when ferric iron oxide/oxyhydroxides, including amorphous and poorly crystalline Fe(III) phases, were solubilized. The residual primary and secondary mineral phases remained stable in the sediments until they were exposed to extremely acidic media analogous to strongly reducing conditions. Manganese is not involved in phosphorus retention to the same extent as iron. Aluminium phases present were released from surface complexes with relative ease and also from mineral structures under the prevailing conditions. The results show a strong agreement between aluminium and phosphorus suggesting it is associated with various aluminium phases to some extent. The sediments of Lake Rotorua are rich in organic-bound P which is released when organic material is oxidized under conditions analogous to anaerobic degradation. The degradation of refractory organic material represents a significant source of phosphorus for incorporation into diagenetic minerals forming in oxic and anoxic layers of the sediment. Heavy liquid separation of the sediments concentrated the small quantities of dense minerals into a separate fraction and the presence of iron sulfides could be verified. Three density fractions obtained by this method separated the diatoms (d less than 2.6 g cm-3), the silicates (d greater than 2.6 less than 3.7 g cm-3) and the heavy minerals (d greater than 3.7 g cm-3) present in the sediment sample. In the heavy mineral phase spherulitic framboidal pyrite and rhombohedrial siderite were observed by scanning electron microscopy (SEM). Energy dispersive x-ray fluorescence (XRF) analysis of the framboidal pyrite detected significant fluorescence's for sulphur and iron. The elemental analysis of siderite characterised it as an iron-rich, non-sulfidic particle with no phosphorus fluorescence. Particles were also observed that had a variable morphology to the framboidal pyrite minerals but similar ratio of Fe to S in the XRF spectrum. It is likely they are other stable forms of iron sulfides or pyrites in various stages of diagenetic dissolution. Digestion of the three density fractions shows the heavy mineral phase is significantly enriched in sulfur and in iron confirming the presence of sulfides. The sulfide-forming trace metals are concentrating in the heavy mineral phase but a progressive enrichment of trace metals down core is not found in the results. Many of the trace elements show maximum concentrations in the Tarawera tephra. There is a good agreement between iron and phosphorus in both treatments that implies iron phases are the predominant phosphorus fixers in the sediments of Lake Rotorua. However the identity of the phosphorus sink could not be confirmed by SEM or XRF analysis of the heavy minerals. The most likely explanations for the observed concentrations of iron and phosphorus and enrichment in the heavy mineral fraction are the persistence of the highly insoluble crystalline iron oxyhydroxides (goethite) in reducing sediments or the formation of the reduced iron mineral vivianite. Considering the density of vivianite it would have being taken into the heavy fraction by default which would account for the enrichment demonstrated by the solution analysis.

Temperate mixed carbonate-siliciclastic sediments and authigenic minerals are the current surficial deposits at shelf and slope depths (30-1015 m water depth) on the north Kaipara continental margin (NKCM) in northern New Zealand. This is the first detailed study of these NKCM deposits which are described and mapped from the analysis of 54 surficial sediment samples collected along seven shorenormal transects and from three short piston cores. Five surficial sediment facies are defined from the textural and compositional characteristics of this sediment involving relict, modern or mixed relict-modern components. Facies 1 (siliciclastic sand) forms a modern sand prism that extends out to outer shelf depths and contains three subfacies. Subfacies 1a (quartzofeldspathic sand) is an extensive North Island volcanic and basement rock derived sand deposit that occurs at less than 100-200 m water depth across the entire NKCM. Subfacies 1b (heavy mineral sand) occurs at less than 50 m water depth along only two transects and consists of predominantly local basaltic to basaltic andesite derived heavy mineral rich (gt30%) deposits. Subfacies 1c (mica rich sand) occurs at one sample site at 300 m water depth and contains 20-30% mica grains, probably sourced from South Island schists and granites. Facies 2 (glauconitic sand) comprises medium to fine sand with over 30% and up to 95% authigenic glauconite grains occurring in areas of low sedimentation on the outer shelf and upper slope (150-400 m water depth) in central NKCM. Facies 3 (mixed bryozoan-siliciclastic sand) consists of greater than 40% bryozoan skeletal material and occurs only in the northern half of the NKCM. Facies 4 (pelletal mud) occurs on the mid shelf (100-150 m water depth) in northern NKCM and comprises muddy sediment dominated by greater than c. 30% mixed carbonatesiliciclastic pellets. Facies 5 (foraminiferal mud and sand) contains at least 30% foraminifera tests and comprises two subfacies. Subfacies 5a consists of at least 50% mud sized sediment and occurs at gt400 m water depth in southern NKCM while subfacies 5b comprises gt70% sand sized sediment and occurs at mid to outer shelf and slope depths in the northern NKCM. vi A number of environmental controls affect the composition and distribution of NKCM sediments and these include: (1) variable sediment inputs to the NKCM dominated by inshore bedload sources from the south; (2) northerly directed nearshore littoral and combined storm-current sediment transport on the beach and shelf, respectively; (3) offshore suspended sediment bypassing allowing deposition of authigenic minerals and skeletal grains; (4) exchange between the beach and shelf producing similar compositions and grain sizes at less than 150 m water depth; and (5) the episodic rise of sea level since the Last Glaciation maximum approximately 20 000 years ago which has resulted in much sediment being left stranded at greater depths than would otherwise be anticipated. Sedimentation models developed from other wave-dominated shelves generally do not appear to apply to the NKCM sediments due to their overall relative coarseness and their mosaic textural characteristics. In particular, the NKCM sediments do not show the expected fining offshore trends of most wavedominated shelf models. Consequently, sandy sediments (both siliciclastic and authigenic) are most typical with mud becoming a dominant component in southern NKCM sediments only at greater than 400 m water depth, over 350 m deeper than most models suggest, a situation accentuated by the very low mud sediment supply to the NKCM from the bordering Northland landmass.

Une grande partie de cette thèse est dédiée à la chimie des isonitriles: ainsi plusieurs chapitres traitent des interactions entre isonitriles et dérivés d'acides, une part importante y a été consacrée à la valorisation des pyruvamides fluorés obtenus par addition d'isonitriles sur l'anhydride trifluoroacétique. Il nous a ainsi été possible de démontrer l'intérêt des hydrates de trifluoropyruvamides en tant qu'électrophiles vis à vis de cétones et de dérivés nitrés. Des tentatives de couplages pinacoliques de pyruvamides nous ont par la suite entraîné vers l'étude d'une réduction très originale d'aldéhydes aromatiques par le diméthylphosphite. Le mécanisme implique probablement un réarrangement de type Phospha-Brook avec formation directe de phosphates benzyliques. Quelques applications synthétiques de cette réaction ont été testées avant de revenir sur la chimie des isonitriles. Nous avons pu combiner une réaction de type Ugi avec une cyclisation de N-acyliminium dans une synthèse très courte de dicétopipérazines tricycliques.

Amino acid biosynthesis is an essential process in living organisms. Certain amino acids can be synthesized by some organisms but not by others. L-Lysine is one of the essential amino acids that bacteria can synthesize but humans cannot. This is somewhat inconvenient for humans as much of their L-lysine must come from their diet. However, the lack of the lysine biosynthetic pathway in humans makes the bacterial enzymes within the pathway attractive drug targets. Recently, a novel lysine biosynthetic pathway was discovered in plants, Chlamydiae and some archaea. It is called the diaminopimelate aminotransferase (DAP-AT) pathway. In this pathway, LL-DAP-AT plays a key role by directly converting L-tetrahydrodipicolinate to LL-DAP in a single step. This is a quite interesting characteristic of LL-DAP-AT as the above conversion takes three sequential enzymatic steps in the previously known lysine biosynthetic pathways. Due to its absence in humans, LL-DAP-AT would be an attractive target for the development of novel antibiotics. In order to understand the catalytic mechanism and substrate recognition of LL-DAP-AT, the structural characterization of LL-DAP-AT is of paramount importance. In this thesis, the overall architecture of LL-DAP-AT and its substrate recognition mechanism revealed by the crystal structures of LL-DAP-AT from Arabidopsis thaliana and Chlamydia trachomatis will be discussed. The crystal structure of the native LL-DAP-AT from A. thaliana (AtDAP-AT) presented in this thesis is the first structure of LL-DAP-AT to be determined. This structure revealed that LL-DAP-AT forms a functional homodimer and belongs to the type I fold family of PLP dependent aminotransferases. The subsequent determination of the substrate-bound AtDAP-AT structure showed how the two substrates, (LL-DAP and L-Glu) significantly different in size, are recognized by the same set of residues without significant conformational changes in the backbone structure. In addition, the LL-DAP-bound AtDAP-AT structure shows that the C-amino group of LL-DAP is recognized stereospecifically by the active site residues that are unique to the family of LL-DAP-AT enzymes. Lastly, the chlamydial LL-DAP-AT presented in this thesis shows a new open conformation for LL-DAP-AT. The implications of the conformational flexibility of CtDAP-AT on the differences in substrate specificities among LL-DAP-AT are discussed.