This study used Vanadium (III) reduction- chemiluminescence method to measure the very low concentration of nitrite plus nitrate (N+N) in oligotrophic seawaters with a detection limit of 0.7nM. In addition, the high temperature catalytic oxidation (HTCO) ¡V chemiluminescence method was applied to determine the concentration of total dissolved nitrogen (TDN) with a detection limit of 0.5£gM based on a volume of 150£gL seawater. Both methods have high degree of precision and accuracy. Furthermore, the Magic method and persulfate oxidation method were conducted to measure the concentrations of soluble reactive phosphorus (SRP) and total dissolved phosphorus (TDP) with detection limits about 10 nM (original seawater) and 100 nM, respectively. All these analytical methods meet the ranges of parameters in most oligotrophic oceans. According to the hydrology data, the Kuroshio of east Taiwan may be classified into four types: 1. Kuroshio Waters affected by the East China Seawater (ECS-KW)¡F2. typical Kuroshio Waters (KW)¡F3. Kuroshio Waters affected by the South China Seawater (SCS- KW) and 4.Kuroshio waters affected by riverplume (plume- KW). In the euphotic zone, the concentrations of N+N, SRP, DON and DOP in the plume-KW are about 0.6 ~ 4 £gM, 0.03 ~ 0.4 £gM, 2 ~ 6 £gM, and 0.05 ~ 0.2 £gM, respectively, higher than those in other type waters. The plume-KW is apparently influenced by the input of freshwater. Besides, the nitrogen and phosphorus species in the SCS-KW and ECS-KW are higher than those in the KW. Positive correlations are significant between Ch1 a and DON and DOP, indicating that biological activity controls primarily on the distributions of DON and DOP in the euphotic zone. KW has oligotrophic characteristics, and in the euphotic zone, the concentrations of N+N and SRP are generally lower than those in other water types. The Chl a has positive correlations with DON and N+N, resulted likely from their same features of subsurface maxima. The ratio between N+N and SRP in the euphotic zone is about 0.02~0.15, and the value increases gradually in deep water, and eventually close the Redfield ratio. Judging from the distribution of the nitrate anomaly (2.5~ 1.5£gM), nitrogen fixation may prevail in the KW. The N+N and SRP values in the euphotic zone in the SCS-KW near the southeastern coast of Taiwan are about 0.02£gM higher in spring than in summer. DON and DOP are also about 1~2.5£gM and 0.02~0.2£gM higher, respectively, in spring than in summer. This feature may be caused from getting stratification torward the summer season in the SCS-KW.

A transverse heated filter atomizer (THFA) was applied to the direct determination of Cd and Pb in urine, and its analytical performances were investigated using a PerkinElmer SIMAA 6000 atomic absorption spectrometer. Seronorm certified human urine reference materials and six realistic samples collected locally were used for the method validation. The urines were diluted ten- or five-fold with 0.2% HNO3. Cd and Pb nitrate solutions were employed as standards. Recoveries of the elements from the urine samples were investigated with the analyte addition method. Compared to the transverse heated graphite atomizer (THGA) with a platform, the THFA provided a significant reduction of spectral background and chemical interferences from the urine matrix, without the use of chemical matrix modifiers, a 1.5–2 times increase of the determination sensitivity and, therefore, a reduction of limits of detection up to 0.018 and 0.2 mg L21 for Cd and Pb, respectively. The use of a THFA collector made from carbon fiber and a tungsten wire improved recoveries of lead and cadmium in urine (¢92%). A sampling temperature 150 uC enabled us to skip the drying period, thus a significantly reduced temperature program was obtained. The accuracies of the measurements of Cd and Pb in the Seronorm urine materials were in good agreement with the recommended values: 4.1 ¡ 0.1 mg L21 of Cd (recommended 5) and 92 ¡ 1 mg L21 of Pb (recommended 85). The lifetime of the THFA for Pb determination was longer than 700 firings, with the sensitivity loss not more than 25% after 500 firings.

Nitrate leaching from research and commercial potato rotations was evaluated using stainless steel zero tension lysimeters, tile drainage and soil samples. The effect of nutrient management versus conventional fertility on marketable potato yield was also investigated. Neither the lysimeters nor the tile lines were able to detect a significant treatment effect on the concentration of NO3--N in collected water samples. However, trends in the NO3--N concentration conformed to nutrient application. Soil samples detected similar trends in soil NO3--N at the research site. Nutrient management fertility had no significant effect on marketable potato yield or soil NO3--N at the commercial sites. A significant crop effect on soil NO3--N was detected. Fall soil samples indicated excess NO3--N in the soil following potato harvest suggesting an overuse of nitrogen fertilizer.

Organic nitrates such as glyceryl trinitrate (GTN) are commonly used to treat cardiovascular disease. They are prodrugs that require bioactivation for pharmacological activity. Currently, there are two proposed pathways of organic nitrate activation: a high-affinity pathway for high-potency nitrates (GTN and pentaerythrityl tetranitate) and a low-affinity pathway for low-potency nitrates (isosorbide dinitrate (ISDN) and isosorbide mononitrate). A major limitation in the utility of organic nitrates is the rapid onset of tolerance during chronic treatment. Inhibition of the enzymes responsible for bioactivation has been put forward as the major cause of tolerance, and aldehyde dehydrogenase 2 (ALDH2) has been proposed as the primary enzyme responsible for bioactivation in the high-affinity pathway. ALDH2 activity is decreased in GTN-tolerant tissues and it has been suggested that ALDH2 inactivation is the underlying cause of GTN tolerance. However, several aspects of this hypothesis are problematic. My objective was to develop an in vivo model of ISDN tolerance and to use this model to examine the effects of chronic ISDN treatment on ALDH2 activity and on organic nitrate-induced vasodilation. The hypothesis of my research is that the reduced potency of GTN caused by ISDN tolerance is mediated by a mechanism independent of ALDH2 inactivation. ISDN tolerance was induced in rats using an in vivo model in which animals were exposed to 0.8 mg/hr ISDN for 24-96 hr. ALDH2 activity was measured in liver mitochondrial fractions and tolerance was assessed in isolated aortic preparations. There was no inhibition of mitochondrial ALDH2 activity in ISDN-treated animals. However, chronic treatment with ISDN resulted in parallel rightward shifts of both the ISDN and GTN concentration-response curves, which increased with increased duration of exposure iii to ISDN. Concentration-response curves for acetylcholine (ACh), sodium nitroprusside (SNP), and diethylamine NONOate were unchanged in ISDN-treated animals. The model of chronic ISDN treatment results in cross tolerance to GTN but does not affect ALDH activity. The data presented in this study indicate no role for ALDH2 in the development of nitrate tolerance. / Thesis (Master, Pharmacology & Toxicology) -- Queen's University, 2011-05-30 12:06:05.785

No description available.

In this study, several aspects of nitrate assimilation and transport have been studied using the filamentous fungus Aspergillus nidulans, which has been shown to be safe laboratory organism as judged by it's pathogenicity towards insect larvae. In silico analysis of the A. nidulans genome sequence, identified two putative genes designated cnxL and cnxK that might be involved in molybdenum cofactor (a component of nitrate reductase) biosynthesis as well as two putative nitrate reductases encoding genes niaB and niaC. All four genes are hitherto unknown. Although many features of these proteins provided clues of functionality, biochemical and genetical approaches employed in this present study failed to elicit expression of any of these four genes. A NrtA protein structure model was developed based on residue homology with the E. coli GlpT a protein, the structure of which has been solved. The results of thiol cross-linking of three double cysteine mutants in four NrtA essential residues, R87, R368, N168 and N459, indicated that the molecular distance between R87 and R368 is ~ 0.4 Å, R368 and N168 ~ 6.2 Å, R87 and N459 is ~ 2.2 Å. Another important observation was the change in the confirmation of Tm 2 and Tm 8 in the presence of nitrate. This shift resulted in an increase of ~ 2 Å gap between the residues R87 and R368. Distances between amino acid residue pairs estimated using such molecular rulers contradicted the NrtA existing model. Cysteine-scanning mutagenesis studies were extended to the generation of a library of single cysteine mutants of NrtA residues spanning Tm 2 and Tm 8. The majority of single cysteine mutants possessed wild type NrtA protein expression levels but unfortunately most were found to be loss-of-function. Consequently, thiol chemistry of this crop of mutants was not perused. Attempts were also made to overexpress and crystallise the bacterial nitrate transporters but none of the transporter tested proved to be a successful candidate for crystallisation. In this regard, bacterial nitrate transporters, NarU (E. coli), Nar (Bacillus cereus), NarK1 and NarK2 (Pseudomonas aeruginosa) and NarK2 (Thermus thermophilus) fused with GFP were expressed in E. coli and used in crystallisation trials. Although this approach has proved successful for a number of membrane proteins, unfortunately was not helpful with regard to the purification of any of the above bacterial nitrate transporters to yield protein expression levels required for successful protein crystallography. Finally, the effects of potential nitrate transport inhibitors were studied on net nitrate transport by NrtA and NrtB proteins of A. nidulans. The results indicated that chlorate had more of an inhibitory effect on NrtA net nitrate transport than that by NrtB. Chlorite and sulphite equally affected net nitrate transport by either NrtA or NrtB proteins while caesium strongly inhibited the net nitrate transport by NrtB transporter.

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No description available.

Methane can be a potentially inexpensive, widely available electron donor for biological denitrification of wastewater, landfill leachate or drinking water, while no studies have clearly shown nitrate reduction to nitrogen gas. Recently anaerobic methane oxidation (AMO) coupled to partial denitrification (nitrite to nitrogen gas) was found by several studies. A microbial consortium, enriched from anoxic sediments, oxidized methane to carbon dioxide coupled to denitrification in the complete absence of oxygen, though the rates and pathways of AMO coupled to denitrification are still poorly understood. In this study, direct AMO coupled to denitrificaiton of nitrate was proved to be possible and its kinetic parameters were experimentally determined. Using a set of batch experiments designed to provide the best estimates of each parameter, these parameters were obtained: maximum specific growth rate (??max) = 0.121/day, maximum substrate consumption rate (qmax) = 1.63 mg COD/mg cells-day, true yield (Y) = 0.074 mg cells/mg COD, half maximum-rate substrate concentration (Ks) = 85 ??M CH4, and endogenous decay rate (b) = 0.03/day. This study firstly characterized kinetic parameters of anaerobic methanotrophic denitrifiers, which will substantially help understand anaerobic methane oxidation in natural systems and accelerate methane-utilizing denitrification in engineering systems.

A range of ion-selective electrodes (ISEs) for the determination of nitrate has been produced based upon rubbery membranes having covalently bound betaine salt sensor molecules. The best performing electrode contained N,N,N-triallyl leucine betaine (6.5 % m/m) covalently bound to polystyrene-block-polybutadiene-block-polystyrene (SBS) (43.5% m/m), with 2-nitrophenyIoctyl ether (2-NPOE) as solvent mediator (40 % m/m) and dicumyl peroxide (DCP) as free radical initiator (10% m/m). The Nemstian slope was -59.1 mV per decade over a linear range of 1 x 10'^-5 x 10"^ mol dm'^ nitrate, a limit of detection of 0.34 pmol dm'^ nitrate and a selectivity coefiBcient for nitrate against chloride ( ^ ° N 0 3 . , CI-) of 3.4 X IQ"^. The speed of response was less than 1 minute over the linear Nerastian range. The lifetime in the laboratory exceeded 5 months with no potentiometric drift over the linear Nemstian range. Temperafure dependency (0-25°C), pH range (2-12) and a selection of interfering anions (F', CI", B r , T, SCN, CIO4", HCO3", NO2", S04^ phthalate) were studied. A field evaluation by continuous immersion in both agricultural drainage weirs and a river were undertaken. The nitrate results obtained with the ISEs compared very favourably (R^=0.99) with those obtained with a segmented-flow instmment in a concentration range 0.47-16 ppm nitrate-N. The electrodes perfonned continuously for over 5 months in mnoff water from a field and over 2 months in river water. The ISEs did not require recalibration and no deterioration in performance or fouling of the membrane surface was observed. A preliminary investigation of a phosphate ionophore based upon a heterocyclic macrocycle was also undertaken. This work, based on previous literature, resulted in a dibasic phosphate electrode having a linear Nemstian range from 3 x lO"'' to 1 x 10"^ mol dm'^, a slope of -27 mV per activity decade and a Umit of detection of 1 x 10"^ mol dm"^ HP04^".