Showing papers on "Urea published in 1977"

Urea reduction of NOx in fuel rich combustion effluents

Abstract: Method of reducing NO x in fuel rich combustion effluents is provided comprising introducing urea at temperatures in excess of about 1900° F. in the presence of excess fuel, wherein said urea is introduced either as a solid or solution in amounts sufficient to reduce the NO x concentration.

Nitrogen Metabolism in Soybean Tissue Culture II. Urea Utilization and Urease Synthesis Require Ni2

Abstract: Potassium citrate (10 mM, pH 6) inhibits the growth of cultured (Glycine max L.) cells when urea is the sole nitrogen source. Ureadependent citrate toxicity is overcome by three separate additions to the growth medium: (a) NH(4)Cl (20 mM); (b) high levels of MgCl(2) (10 mM) or CaCl(2) (5-10 mM); (c) low levels of NiSO(4) (10(-2) mM). Additions of 10(-2) mM NiSO(4) not only overcome citrate growth inhibition but the resultant growth is usually better than urea-supported growth in basal medium (neither added citrate nor added nickel). In the absence of added citrate, exceedingly low levels of NiSO(4) (10(-4) mM) strongly stimulate urea-supported growth in suspension cultures.Citrate does not inhibit growth when arginine is sole nitrogen source. However, cells using arginine have no net urease synthesis in the presence of 10 mM potassium citrate. When 10(-2) mM NiSO(4) is added to this medium, urease specific activity is 10 times that observed in basal medium lacking both citrate and added nickel.Citrate is a chelator of divalent cations. That additional Mg(2+) or Ca(2+) alleviates urea-dependent citrate toxicity indicates that citrate is acting by chelation, probably of another trace divalent cation; this is probably Ni(2+) since at 10(-2) mM it overcomes citrate toxicity and at 10(-4) mM it stimulates urea-supported growth in the absence of citrate. That ammonia overcomes citrate toxicity indicates that the trace Ni(2+) is essential specifically for the conversion of urea to ammonia. Ni(2+) stimulation of urease levels in arginine-grown cells supports this contention.In basal medium, soybean cells grow slowly with urea nitrogen source presumably because the trace amounts of Ni(2+) present (

Urease of Klebsiella aerogenes: control of its synthesis by glutamine synthetase.

Abstract: Urease was purified 24-fold from extracts of Klebsiella aerogenes The enzyme has a molecular weight of 230,000 as determined by gel filtration, is highly substrate specific, and has a Km for urea of 07 mM A mutant strain lacking urease was isolated; it failed to grow with urea as the sole source of nitrogen but did grow on media containing other nitrogen sources such as ammonia, histidine, or arginine Urease was present at a high level when the cells were starved for nitrogen; its synthesis was repressed when the external ammonia concentration was high Formation of urease did not require induction by urea and was not subject to catabolite repression Its synthesis was controlled by glutamine synthetase Mutants lacking glutamine synthetase failed to produce urease, and mutants forming glutamine synthetase at a high constitutive level also formed urease constitutively Thus, the formation of urease is regulated like that of other enzymes of K aerogenes capable of supplying the cell with ammonia or glutamate

Plasma creatinine and urea: creatinine ratio in patients with raised plasma urea

Abstract: We examined the plasma urea and creatinine concentrations and the ratio between them according to diagnosis in 100 unselected and 31 selected adult hospital patients with a plasma urea concentration greater than or equal to 10 mmol/l (60mg/100ml). We also examined plasma urea and creatinine concentrations in 350 unselected consecutive patients, but found no useful relation between the two values. Congestive heart failure was the most common identifiable cause of a raised plasma urea concentration in the 100 unselected patients (36%). Among these 100 patinets the plasma creatinine concentration was a more useful discriminant between prerenal uraemia and intrinsic renal failure than was the urea:creatinine ratio or the plasma urea concentration. A plasma creatinine concentration greater than 250 mumol/1 (2-8 mg/100ml) indicated intrinsic renal failure with a 90% probability.

Conformational states of chromatin в bodies induced by urea

Abstract: Monomer chromatin nu bodies (nu1) from chicken erythrocyte nuclei were exposed to 0-10 M urea plus 0.2 mM EDTA (PH 7). Alterations in nu1 conformation were examined using hydrodynamic methods (i.e., S, eta, and (formula: see text)), thermal denaturation, circular dichroism, reactivity of histone thiol groups to N-ethyl maleimide, and electron microscopy. The two domains of a nu body (i.e., the DNA-rich shell and the protein-rich core) aeared to respond differently to the destabilizing effects of increasing urea; DNA conformation and stability exhibited noncooperative changes; the core protein structure revealed cooperative destabilization between 4 and 7 M urea. Companion studies on the conformation of the inner histone "heterotypic tetramer" also revealed cooperative destabilization with increasing urea concentration.

The protein-sparing effect of carbohydrate: 2.* The role of insulin

Abstract: 1. In five experiments with growing female pigs of 38-63 kg, insulin (2 mU/kg) per min) and glucose (9-17 mg/kg per min) were infused continuously for 3-7 d. In three further experiments, glucose (9 mg/kg per min) was infused alone for 5 d. 2. In response to the combined infusion, plasma insulin increased 2-7-fold, plasma glucose decreased, on average, by 50% and plasma urea concentration was reduced by 40%. Urinary excretion of urea and nitrogen decreased after the first day of infusion to values averaging 70% of control levels. 3. The infusion of glucose alone provoked only a small increase in plasma insulin. The reduction of urinary urea and of N excretion were approximately 25% of those observed with the combined infusions.

Inhibition of conditions arising from microbial production of ammonia

Abstract: Methods, compositions and products are described which inhibit the development of undesirable conditions arising as a result of microbial formation of ammonia from urea in excreted urine. Amino acid compounds are employed.

The origin and fate of salivary urea and ammonia in man.

Abstract: 1. Saliva obtained from the parotid duct of normal and uraemic subjects had an average urea concentration of 86% of the plasma concentration whereas in mixed saliva obtained from the mouth the urea concentration was only 31% of the plasma concentration. Ammonia concentrations were low or unmeasurable in parotid saliva but varied between 0·6 and 26 mmol/kg in oral saliva, showing a positive correlation with the plasma urea concentration. 2. The urea in samples of mixed oral saliva incubated at 37°C disappeared by 290 min. Ammonia steadily increased during incubation; within the first 100 min, the increase could be largely accounted for by bacterial hydrolysis of urea, but later non-urea sources became relatively more important. 3. These findings suggest that the ammonia in mixed oral saliva is derived by bacterial hydrolysis of urea within the mouth. However, the concentration of ammonia plus urea nitrogen in oral saliva was only 76% of the urea nitrogen concentration of parotid saliva, which suggests that some ammonia is lost from the mouth by buccal absorption or by volatilization. 4. To assess the role of non-ionic diffusion of ammonia through the buccal mucosa, we studied the effect of pH on the disappearance of ammonia from buffered solutions retained in the mouth. Ammonia concentrations fell more rapidly at pH 9 than at pH 7, as also did those of hydrazine, a non-volatile analogue of ammonia which is known to be absorbed through other mucosae by non-ionic diffusion. These findings suggest that salivary ammonia is reabsorbed passively through the oral mucosa in the un-ionized phase.

Proteolysis of αs1-casein by chymosin: influence of pH and urea

Abstract: The specificity of chymosin on αs1-casein was shown to be dependent on the reaction pH and on the state of aggregation of the substrate. In aqueous solution αs1-casein was optimally hydrolysed to αs1-I at pH 5·8; if the casein was solubilized in the isoelectric region by the use of 5 M-urea, optimum proteolysis occurred at pH 2·8. Hydrolysis of αs1-I to yield αs1-II, αs1-III and αs1-IV occurred at pH values > 5·8 in the presence or absence of urea. In the isoelectric region αs1-II, αs1-III and αs1-IV were not formed in the absence of urea where the substrate was aggregated: instead a peptide αs1-V was produced; at the same pH and using urea as a solubilizing agent αs1-II, αs1-III and αs1-IV were formed together with a further peptide αs1-VI.

Separative pathways for urea and water, and for chloride in chicken erythrocytes.

Abstract: 1. Urea and water permeabilities of chicken erythrocytes are considerably lower than those of mammalian red cells. 2. The permeabilities to urea, thiourea and to N-methylurea (about 10(-6) cm/sec at 25 degrees C) were independent of concentration within a very broad range, and we found no evidence of interaction between transport of analogue molecules. The activation energies were between 17 and 19 kcal/mole, and urea transport was not inhibited by phloretin, which inhibits urea transport in mammalian red cells. 3. The water permeability of chicken red cells (as measured by the diffusion of tritiated water) was 1-35 X 10(-3) cm/sec at 25 degrees C. The activation energy was 10 kcal/mole, and the water permeability was not affected by phloretin or parachloromercuribenzoate. 4. It is concluded that the urea and water permeabilities of the chicken erythrocyte membrane are similar to those of a non-porous bimolecular phospholipid membrane. 5. Like the red cells of other animal species the chicken red cell membrane contains an anion transport system, mediating a rapid exchange of chloride across the cell membranes. The pH dependence, temperature dependence, and sensitivity to inhibitors were similar to the properties of the anion transport system found in mammalian red cells. Our study shows, therefore, that the transport system offers a highly specific pathway to the exchange of anions, without presenting an inspecific leak to the permeation of water and urea.

Ammonium and urea uptake by some freshwater algae

Abstract: Nitrogen deficiency increases the initial saturated rate of ammonium and urea uptake by three green and three blue-green algae. The increase caused by N deficiency is greater in darkness than in th...

Effect of urea concentration on growth of Ureaplasma urealyticum (T-strain mycoplasma).

Abstract: The effect of urea on growth of Ureaplasma urealyticum type VIII was studied by cultivating the organisms in a dialysate broth, prepared from soy peptone and autoclaved yeast, supplemented with 5% dialyzed horse serum, 100 mM 2-(N-morpholino)ethane sulfonic acid buffer (pH 5.75), and defined amounts of urea. Without urea, growth did not occur. Total growth was directly related to urea concentration. The least amount of urea that supported growth was 0.032 mM, which resulted in 3 x 10(4) colony-forming units per ml. The maximum yield of organisms, 8.0 x 10(7) colony-forming units per ml, was observed at 32 mM urea. Growth was limited not only by urea concentration, but also by the buffer capacity of the medium. The maximum amount of 2-(N-morpholino)ethane sulfonic acid buffer that could be employed was 100 mM; at higher concentrations, growth was inhibited. The yield of U. urealyticum was small even in medium with 32 mM urea and 100 mM 2-(N-morpholino)ethane sulfonic acid buffer: 0.63 mg of protein per liter of culture containing 5 x 10(10) total colony-forming units. The molar growth yield was 20 mg of protein per mol of urea. The growth rate was also a function of urea concentration. Generation times ranged from 8 h at 0.032 mM urea to 1.6 h at 3.2 mM urea, where the substrate level was saturating. The K(s) value for growth was 2.0 x 10(-4) M urea. Thus, urea is a growth-limiting factor for U. urealyticum, but remarkably large amounts of this substrate are required.

Acid‐base induced alterations in glutamine metabolism and ureogenesis in perfused muscle and liver of the rat

Abstract: . The effects of altered acid-base balance on the production of urea and the metabolism of glutamine were investigated in the isolated perfused liver and hind-quarter of the rat. In the isolated perfused rat liver, lowering of perfusate pH without altering bicarbonate concentration significantly reduced urea production and increased net glutamine synthesis, although the converse did not obtain. In the isolated perfused rat hindquarter when perfusate pH and bicarbonate were simultaneously reduced glutamine synthesis was significantly increased. The combined hepatic and muscle increase in glutamine synthesis accounted for 89% of the decrease in hepatic urea synthesis under these experimental conditions. These changes in nitrogen metabolism are interpreted in terms of adaptations which offset the initial alterations in hydrogen ion homeostasis.

Movement of nitrate-N and transformations of urea-N under field conditions

Abstract: Summer and winter sodium nitrate treatments at 400 kg N/ha were given to ryegrass pasture on Horotiu sandy loam. The movement and adsorption of nitrate were studied under natural precipitation and ground water flow. Movement of nitrate to depths of 400 mm could be explained by miscible displacement when the soil was near field capacity, and movement was faster under unsaturated flow conditions. Adsorption measurements showed that the soil had an anion exhange capacity of 0.85 me./100 g in 0.025m CaCl2. These positively charged sites were able to retard nitrate movement below 400 mm. Simulated urine treatments were also made at 2-monthly intervals at rates of 200–400 kg N/ha as urea. The transformations in exchangeable nitrogen were studied. Hydrolysis of urea was complete in 2 days in summer and 3 days in winter. Nitrification was not appreciable until after 7 days in all seasons. At soil temperatures of 7.5–10°c nitrification continued to be slow and was not complete until 60 days, but at temper...

Effect of urea on the heat coagulation of the caseinate complex in skim-milk

Abstract: Additions of urea progressively increased the heat stability of milk outside of its coagulation time (CT)–pH minimum. In the region of the CT–pH minimum larger amounts of urea were required before an increase in heat stability occurred. The effect of urea was observed over the temperature range 125–140 °Cfornaturalmilk, milk which had been dialysed against synthetic sera, and milk to which a sulphydrylblocking agent had been added. Urea additions did not affect the activation energy of the heat coagulation reaction or the stability of milk to rennet or ethanol.

Fertilizer composition and method of making same

Abstract: A method for controlled reaction of urea with sulfuric acid to form a liquid nitrogen sulfate fertilizer composition consisting of urea sulfate and liquified urea, and which may include other nutrients.

Interactions between dietary carbohydrate and nitrogen and digestion in sheep

Abstract: Rumen fermentation, duodenal digesta flow and N balance were studied in three sheep fed diets which contained urea or fishmeal as nitrogen supplement and either barley straw, barley + corn starch or molassed wheat straw (60% molasses) as carbo-hydrate source.The molar composition of rumen volatile fatty acids (VFA) with straw diets was high in acetate (64–68%), with barley diets high in propionate (32–36%) and with molasses diets high in butyrate (28–34%). Rumen ammonia concentrations (RAC) were low and constant with fishmeal diets (< 10 mM) but varied with carbohydrate source with urea diets. RAC was very high (24 mM) after feeding molasses + urea.With barley and molasses diets 73–75% of digestible dry matter (DDM) was digested in the stomach, but only 54–59% with ground and pelleted straw diets. For all diets less N passed the duodenum than was eaten. The lowest daily duodenal N passage was with molasses + urea. Daily urinary N output was highest (P < 0·01) for this diet and nitrogen balance lowest.Daily intakes of amino acids differed widely between diets but differences in duodenal passage were not so great. Molasses + urea provided the lowest values for daily duodenal amino acid flow. The amino acid content of duodenal N (mM amino acid/16 g N) was relatively constant despite broad variation between diets. Digesta alanine and valine (mM/16 g N) were higher for barley than for straw diets (P < 0·05). Digesta methionine (mM/16 g N) was lower for fishmeal than for urea diets (P < 0·01).Very little sucrose reached the duodenum with any diet.It was concluded that the form of energy-yielding nutrient inuflenced duodenal N flow by affecting ammonia-N capture in the rumen, but that the amino acid content of duodenal N was little affected. The interaction between molasses and urea was not beneficial to efficient use of urea-N in this work when molasses was the major carbohydrate component of the diet.

Localization of enzymes in Ureaplasma urealyticum (T-strain mycoplasma).

Abstract: Ureaplasma urealyticum cells were lysed by osmotic shock or by digitonin. The membrane fraction contained four to ten times as much protein as the cytoplasmic fraction. These values are in large excess of those reported for classical mycoplasmas, suggesting that the Ureaplasma membrane fraction was heavily contaminated with proteins derived from the growth medium. The U. urealyticum urease activity was localized in the cytoplasmic fraction, whereas the adenosine triphosphatase activity was localized in the membrane fraction. Significant urease activity could be detected also in nonviable cells. Urea, at concentrations above 0.25 M, was mycoplasmastatic to Acholeplasma laidlawii, Mycoplasma hominis, and U. urealyticum, so that the Ureaplasma urease did not afford preferential protection against urea toxicity. The intracellular localization of the urease would be expected to release ammonia from urea in the cytoplasm. The ammonia will take up protons to become ammonium ions. It can be hypothesized that the intracellular NH4+ plays a role in proton elimination or acid-base balance, which might be coupled to an energy producing ion gradient and/or transport mechanisms.