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Ammonium Level (ammonium + level)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

The dynamics of unattached benthic macroalgal accumulations in the Swan,Canning Estuary

HYDROLOGICAL PROCESSES, Issue 13 2001
Helen Astill
Abstract It has been suggested that macroalgal accumulations may impact on benthic nutrient cycling by promoting remineralization of sedimentary nutrients, otherwise inaccessible, and act as sinks/sources for dissolved nutrients in the water column. However, little consideration has been given to the time taken for these impacts to occur, and if accumulations persist long enough in a region for impacts to occur. In this study, accumulations were characterized seasonally, according to biomass, height relative to water depth, and organic content of the underlying sediment, from November 1996 to August 1997, in the Swan,Canning Estuary. Persistence of accumulations was measured from late summer to mid-winter in 1997, by tagging individual plants and recording the time tagged plants persisted at 10 sites. In summer 1998, physicochemical profiles of accumulations were measured over 24 h, at two locations: one with relatively low sediment organic content (SOCn) (1·5% LOI) and one with relatively high SOC (6% LOI). Accumulations rarely exceeded 25 cm in height, regardless of water column depth, and ranged between 100 and 500 g dwt m,2. Macroalgae persisted between one week, in relatively well-flushed regions, to one month in areas with poor flushing. Over the entire diurnal period, almost 100% of incident light was attenuated at the bottom of all accumulations. Dissolved oxygen levels at the bottom of accumulations were generally depressed, particularly at night, with hypoxia (1 mg l,1) recorded at the high SOC site at 03 : 00 h. No significant differences in FRP concentrations (approximately 30,60 µg l,1) were recorded between sites, or within accumulation profiles. Ammonium levels were greatly raised inside accumulations at the high SOC site by 03 : 00 h (10 and 300 µg l,1, inside and outside, respectively). The results show that, where SOC is high, conditions within accumulations are affected. Impacts occurred within 24 h; well within the period for which accumulations persist. These results also indicate that regulation of hydrological regimes in estuarine systems may result in increased persistence of macroalgal accumulations, and associated water quality problems. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Valproic Acid-Induced Hyperammonemic Encephalopathy with Triphasic Waves

EPILEPSIA, Issue 7 2000
Akira Kifune
Summary: Purpose: To examine a patient with valproic acid (VPA)-induced hyperammonemic encephalopathy accompanied by triphasic waves. Methods: A 61-year-old male patient with epilepsy experienced disturbance of consciousness after VPA dose was increased because of poor seizure control. The electroencephalogram (EEG) taken on admission revealed triphasic waves and high-amplitude ,-activity with frontal predominance. Although serum hepatic enzymes, such as AST and ALT, were normal, serum ammonium level was high at 96 ,g/dl (normal range, 3,47 ,g/dl). Serum amino acid analysis showed multiple minor abnormalities. Administration of VPA was discontinued immediately after admission, while other anticonvulsants were continued. Results: The patient's condition was improved on the fourth day of admission. An EEG, serum ammonium level, and amino acid profile were normal on the eighth day. Based on VPA administration, serum ammonium levels, and results of amino acid analysis, this patient had VPA-induced hyperammonemic encephalopathy. Conclusions: Our case indicates that caution is required if triphasic waves appear in VPA-induced hyperammonemic encephalopathy. [source]

Suillus bovinus glutamine synthetase gene organization, transcription and enzyme activities in the Scots pine mycorrhizosphere developed on forest humus

NEW PHYTOLOGIST, Issue 2 2004
Jarmo T. Juuti
Summary ,,Glutamine synthetase (GS) expression and activity is of central importance for cellular ammonium assimilation and recycling. Thus, a full characterization of this enzyme at the molecular level is of critical importance for a better understanding of nitrogen (N) assimilation in the mycorrhizal symbiosis. ,,Genomic and cDNA libraries of Suillus bovinus were constructed to isolate the GS gene, glnA, and corresponding cDNAs. The transcription initiation site was identified and transcription and enzyme activities were characterized in pure culture mycelium and mycorrhiza, and extramatrical mycelium samples harvested from Scots pine,Suillus bovinus microcosms grown on forest humus. ,,Pure culture mycelium, mycorrhiza and extramatrical mycelium all exhibited equivalent levels of GS transcription, translation and enzyme activities. However, levels of transcription and enzyme activity did not correlate as a large majority of detectable transcripts showed specific 5,-end truncation. ,,Our data suggest that GS is constitutively expressed and not directly affected by environmental conditions of the symbiotic N uptake. Any changes in the intracellular ammonium level are most likely handled by regulatory flexibility of GS at enzyme level. [source]

Ammonia Removal Using Hepatoma Cells in Mammalian Cell Cultures

BIOTECHNOLOGY PROGRESS, Issue 5 2000
Yeon Sook Choi
It was examined whether hepatocyte cell lines can be used for ammonia removal in mammalian cell cultures. It was found that there exists a critical ammonium concentration level for each hepatocyte cell to remove ammonia. Among the cells tested in this work, primary hepatocytes showed the strongest ammonia removal capability if ammonium concentration is higher than the critical level. However, primary hepatocytes lost the liver function gradually and finally died after 2,3 weeks. Because of this limitation, primary hepatocytes were not appropriate to be used for ammonia removal in long-term cultures. Hep G2 cells, which are immortal, also showed a strong ammonia removal activity. The ammonia removal activity of Hep G2 cells depended on the concentration of ammonium in the medium, as in the case of primary hepatocytes. However, urea could not be detected in the course of ammonia removal by Hep G2 cells. Instead of urea, Hep G2 cells secreted glutamine into the culture medium. The capacity for ammonia removal was higher in the absence than in the presence of glutamine. Thus we checked the activity of glutamine synthetase in the Hep G2 cells. The level of glutamine synthetase activity increased with the addition of ammonium chloride. This result accounts for the ammonium concentration dependency of Hep G2 cells in ammonia removal and glutamine synthesis. Furthermore Hep G2 cells could grow well in the absence of glutamine, which was necessarily required in mammalian cell cultures. These results prove that glutamine formation serves as the primary mechanism of detoxifying ammonia in hepatocyte cell lines as expected. In addition, it was demonstrated that ammonium level could be reduced 38% and that erythropoietin production increased 2-fold in the mixed culture of Hep G2 and recombinant CHO cells. [source]