Rate Of Ammonia Release Research Articles

Amino Acid Transport and Metabolism in Relation to the Nitrogen Economy of a Legume Leaf

Net balances of amino acids were constructed for stages of development of a leaf of white lupin (Lupinus albus L.) using data on the N economy of the leaf, its exchanges of amino acids through xylem and phloem, and net changes in its soluble and protein-bound amino acids. Asparagine, aspartate, and gamma-aminobutyrate were delivered to the leaf in excess of amounts consumed in growth and/or phloem export. Glutamine was supplied in excess until full leaf expansion (20 days) but was later synthesized in large amounts in association with mobilization of N from the leaf. Net requirements for glutamate, threonine, serine, proline, glycine, alanine, valine, isoleucine, leucine, tyrosine, phenylalanine, histidine, lysine, and arginine were met mainly or entirely by synthesis within the leaf. Amides furnished the bulk of the N for amino acid synthesis, asparagine providing from 24 to 68%. In vitro activity of asparaginase (EC 3.5.1.1) exceeded that of asparagine:pyruvate aminotransferase (EC 2.6.1.14) during early leaf expansion, when in vivo estimates of asparagine metabolism were highest. Thereafter, aminotransferase activity greatly exceeded that of asparaginase. Rates of activity of one or both asparagine-utilizing enzymes exceeded estimated rates of asparagine catabolism throughout leaf development. In vitro activities of glutamine synthetase (EC 6.3.1.2) and glutamate synthase (EC 1.4.7.1) were consistently much higher than that of glutamate dehydrogenase (EC 1.4.1.3), and activities of the former two enzymes more than accounted for estimated rates of ammonia release in photorespiration and deamidation of asparagine.

Urease assay and ammonia release from leaf tissues

The rate of release of ammonia from leaf tissues of Glycine max and Triticum aestivum suspended in urea solutions was relatively low for initial periods of up to 40 min, due to retention of ammonia by the tissues. Urease, EC 3.5.1.5, could be assayed by the subsequent rate of ammonia release. The method was applied to leaves of 29 other species.

Regulation by Amino Acids of Photorespiratory Ammonia and Glycolate Release from Ankistrodesmus in the Presence of Methionine Sulfoximine

Methionine sulfoximine induced release of ammonia from illuminated cells of Ankistrodesmus braunii (Naegeli) Brunnth, in normal air, but less in air enriched to 3% CO(2). In normal air, methionine sulfoximine also induced glycolate release. Addition of either glutamate, glycine, or serine suppressed glycolate release, whereas glutamate and glycine at the same time stimulated ammonia release. The results indicate that inhibition of glutamine synthetase and thereby inhibition of photorespiratory nitrogen cycling restricts the sink capacity for glycolate in the photorespiratory carbon cycle. An external supply of glutamate, glycine, or serine seems to stimulate glyoxylate transamination and thus partly restores the sink capacity. Calculations of total glycolate formation rates in air from glycolate and ammonia release rates in the presence of methionine sulfoximine and glutamate revealed values of approximately 20 micromoles glycolate per milligram chlorophyll per hour on the average. Similar calculations led to an estimated rate of photorespiratory ammonia release in air, in the absence of methionine sulfoximine, of about 10 micromoles per milligram chlorophyll per hour on the average, a value comparable to the primary nitrogen assimilation rate of 8 micromoles per milligram chlorophyll per hour.

Urea-formaldehyde complexes and their hydrolysis by rumen ureasein vitro

Much attention has been given to the use of urea in ruminant feeds since the demonstration by Hartet al.(1939) that non-protein nitrogen (NPN) compounds could be a substitute for protein in ruminant rations. However, the high activity of urease in the rumen decreases the efficiency of urea utilization, because the rate of ammonia release from urea is much faster than the rate of its assimilation by rumen microbes for the synthesis of amino acids (Bloomfield, Garner & Muhrer, 1960). Moreover, if the concentration of ammonia exceeds a certain limit, it causes toxicity to the animals (Froslie, 1977). The efficiency of urea utilization can be increased if the rate of ammonia production is similar to the rate of its assimilation by rumen micro-organisms. This could be achieved either by decreasing the activity of the rumen urease or by modifications of urea in products which result in slow release of ammonia (Helmer & Bartley, 1971). Attempts have been made to increase the efficiency of urea utilization by complexing urea with carbohydrates (Danielset al.1971; Muhrer, Harris & Bloomfield, 1968; Shultz, Shultz & Chicco, 1972), sodium bentonite (Britton, Cooling & Klopfenstein, 1978) and carboxy resin (Huston, Scherton & Breuer, 1974). Formaldehyde is known to protect proteins from rumen degradation by its reaction with terminal amino groups (NH2), the e-amino groups of lysine and a number of other side-chain groups of proteins (Barry, 1976; Van Dooren, 1972). Urea contains two amino groups for undergoing chemical reaction with HCHO to give different complexes. Previous work in our laboratory has shown that urea could be complexed with HCHO (Lallet al.1980; Pal & Negi, 1977). However, in those studies excesses of urea and HCHO were not removed and this produced an artefact in the evaluation of the ureaformaldehyde complexes (UFCs). Moreover, whole rumen fluid was used forin vitroammonia formation from these complexes. No studies have been made so far in a well-defined system on the biochemical basis of the ammonia-releasing property of the UFCs. We report here the formation and isolation of UFCs, free from urea and HCHO and their hydrolysis with purified rumen urease (EC. 3·5.1.5). Evidence is adduced that UFCs are substrates for rumen urease and can act as slow ammonia-releasing compounds.

Effect of body size and water temperature on the release of dissolved organic carbON AND ammonia in the sand dollar, Mellita quinquiesperforata (Leske)

1. 1. Rate of dissolved organic carbon and ammonia release were measured monthly for 7 months in different size Melitta quinquiesperforata. 2. 2. Small animals release more carbon than large animals and ammonia release is variable with size. 3. 3. Greatest rate of ammonia release occurs in summer (5.5 μg/hr per g dy wt) and least in winter (0.03 μg/hr per g dry wt). 4. 4. Rate of carbon release is variable with the rate in August at 33°C being 36.2 μg/hr per g dry wt and in January at 15°C being 35. μ/hr per g dry wt for medium-size animals.

Timed ammonia release for steers.

Slow and rapid ruminal ammonia release rates were simulated by intermittent urea feeding with steers fed winter range grass. Four 360-kg, ruminally-cannulated steers were fed 208 g prairie hay (2.56% crude protein) hourly with the following daily dietary supplements: (1) Urea provided continuously (C) at a rate of 3.5 g/hr for 24 hr; (2) urea provided moderately (M) at a rate of 14.2 g/hr for 6 hr (3) urea offered rapidly (R) as 85 g in 1 hr, or (4) no supplemental urea (O). Ruminal ammonia remained stable with treatments C and O at 12.8 and 1.6 mg/dl, respectively. Treatments R and M peaked 1.5 and 6.5 hr after the start of urea feeding at 41.8 and 37.1 mg/dl, respectively. Nonammonia nitrogen concentrations in the rumen were increased by an average of 23% with urea supplementation. Dry matter digestibility was increased by 5% with addition of urea, regardless of the rate of urea administration. Daily nitrogen retentions were 12.4, 12.2, 11.4 and -7.1 g (P < .01) for C, M, R and O, respectively. Simulated slow ammonia release rates enhanced neither dry matter digestibility nor nitrogen retention. Metabolic use of ammonia in the rumen of steers fed forage was not improved by an attenuated release rate.

The role of zooplankton in the nitrogen dynamics of a shallow estuary

The rates of ammonia and urea release by selected species of copepods collected from the estuary at Beaufort, North Carolina, during September through April in 1973 and 1974 varied with species, sex, season, and feeding state. The rate of ammonia assimilation by phytoplankton was greatest in September and April, and there were no significant differences associated with tidal changes. Rates of ammonia assimilation by phytoplankton ranged from 1 to 101 mg N m −3 day −1 while ammonia release by Zooplankton ranged from 0.1 to 9.7 mg N m −3 day −1. The productivity of the phytoplankton in the estuary must depend largely upon regenerated nitrogen since the maximum rate of assimilation of ammonia by phytoplankton was often the same as total-nitrogen uptake estimated from primary productivity. The average rate of ammonia release by zooplankton was 8% of the average, ammonia assimilation by phytoplankton. I conclude that, while all sources of regenerated nitrogen are used and therefore of value in a system depending almost totally upon regeneration, Zooplankton are not the major source of regenerated nitrogen in this estuary.

NON-PROTEIN NITROGEN IN CORN SILAGE: A PARTIAL CHARACTERIZATION, ITS UTILIZATION IN THE RUMEN AND EFFECT UPON DIGESTIBILITY AND RETENTION OF NITROGEN IN LAMBS

Three trials were conducted. In trial 1, 30 samples of silage were collected from farms and analyzed. Non-protein nitrogen (NPN) contributed an average of 46.4% to the total N. Of the NPN-N, an average of 10.1% was ammonia-N, 30.4% was alpha amino-N, 1.2% was amide-N and 58.3% was not identified. Extensive variability was demonstrated among samples for all these values except ammonia-N. In trial 2, silage effluents, in which NPN-N was 95% or more of total N, were compared with urea and soybean meal as to ammonia release rates in the rumen after isonitrogenous infusions of each material. Ammonia levels after infusion of corn silage effluent were nearer to those after soybean meal infusion than those after urea infusion. In trial 3, frozen corn (low in NPN) was compared with ensiled corn in a digestion and balance trial using lambs. Nitrogen balance was not significantly different between corns but was improved by supplementing either of them with urea.

Nitrogen regeneration during the degradation of several amino acids by plankton communities collected near Halifax, Nova Scotia, Canada

Nitrogen regeneration accompanying the bacterial degradation of a variety of amino acids supplied at 10.0 μM to samples of coastal plankton communities collected near Halifax, Nova Scotia, Canada was examined. A lag period characterized by a low rate of amino acid uptake and ammonia release was typically followed by a dramatic increase in the rates of uptake and ammonia release. The duration of the lag period varied with the amino acid tested. The ratio of the final ammonia concentration to the nitrogen supplied as amino acid was taken as the regeneration ratio. This value varied from 0.58 to 0.86 for L-arginine and 0.38 to 1.17 for the other amino acids tested, with an average value of 0.74. The presence of inorganic fixed nitrogen at 10.0 μM had no effect on the degradation of L-arginine. Other organic compounds supplied at 10.0 μM decreased the lag period for L-arginine uptake and degradation. Glucose supplied at 50.0 μM decreased the nitrogen regeneration ratio, but did not further decrease the lag for L-arginine degradation. Carbon respiration ratios for L-arginine, L-glutamate, and L-lysine were 0.70, 0.68, and 0.65 when the nitrogen regeneration ratios were 0.86, 0.38, and 0.77, respectively.

Diurnal patterns of ammonia release in marine and terrestrial isopods

1. 1. An inverse exponential relationship between the rate of ammonia excretion and dry body weight has been established in a selected isopod, Cirolana harfordi. 2. 2. Similar diurnal patterns of rate of ammonia release have been demonstrated in eight species of isopods including members of the Oniscoidaea, Valvifera and Flabellifera. 3. 3. C. harfordi exposed to either normal light/dark photoperiodism, continuous light or continuous dark retain a characteristic pattern of ammonia release. 4. 4. Porcellio scaber and Idotea resecatawere found to release ammonia during the afternoon in discrete events, with comparable rates of release. No correlation was found between fecal production and ammonia release.

Metabolism of glutamine and glutamic acid by isolated perfused kidneys of normal and acidotic rats.

1. When isolated kidneys from fed rats were perfused with glutamine the rate of ammonia release at pH7.4 (110-360mumol/h per g dry wt.) was one to two times that of glutamine removal. Glucose formation from 5mm-glutamine was 16mumol/h per g. If kidneys were perfused with glutamine at pH7.1 (10-13mm-sodium bicarbonate) there was no increase in glutamine removal or in the formation of ammonia or glucose. 2. When isolated kidneys from fed rats were perfused with glutamate at pH7.4, glucose formation was 59mumol/h per g, glutamine formation was 182mumol/h per g and ammonia release was negligible. At pH7.1 glutamine synthesis was inhibited and formation of ammonia and glucose were increased. 3. In perfused kidneys from acidotic rats, which had received 1.5% (w/v) NH(4)Cl to drink for 7-10 days, gluconeogenesis from glutamine was enhanced (101mumol/h per g). Glutamine removal and ammonia formation were also increased, compared with the rates in perfused kidney from normal rats. The extra glutamine consumed was equivalent to the extra glucose formed. 4. When the kidney from the 7-10-day-acidotic rat was perfused with glutamate gluconeogenesis was increased (113mumol/h per g). Synthesis of glutamine was decreased, and ammonia release was approximately equal to the rate of glutamate removal. 5. The time-course of these metabolic alterations was investigated after the rapid induction of acidosis by infusion of 0.25m-HCl into the right side of the heart. The increase in gluconeogenesis from glutamine developed gradually over several hours. When kidneys from 6h-acidotic rats were perfused with glutamate, formation of glucose and glutamine were both rapid. 6. In acidotic rat kidneys perfused with glutamine, tissue concentrations of glutamate and glucose 6-phosphate were increased compared with those in control perfused kidneys from non-acidotic rats. 7. The results are discussed in terms of control of the renal metabolism of glutamine. In particular, it is suggested that in acidotic rats glucose formation is the major fate of the carbon of the extra glutamine utilized by the kidney, and that inhibition of glutamine synthetase could contribute to the increase in intracellular ammonia concentration in the kidney.