Showing papers on "Urea published in 1988"

Short-term assay of soil urease activity using colorimetric determination of ammonium

Abstract: A rapid assay for soil urease in the absence of bacteriostatic agents has been developed. The method comprises incubation of soil with an aqueous or buffered urea solution, extraction of ammonium with 1 N KCl and 0.01 NHCl and colorimetric NH4 + determination by a modified indophenol reaction. The method is characterized by high sensitivity and stability of the coloured complex formed. Measurements obtained by this method showed that no change in urease activity occurred when field-moist samples of soils were stored at −20°C for as long as 5 months. Air-drying of field-moist soil samples may lead to an increase in urease activity.

Preparation of spherical, monosized Y2O3 precursor particles

Abstract: Spherical, monosized yttria precursor particles were obtained by homogeneous precipitation in aqueous solutions by reaction with the thermal decomposition products of urea. Increasing [Y 3+ above 0.05 M resulted in a deviation from spherical morphology and caused agglomeration of particles. Over the concentration range studied, excess urea did not affect particle morphology, but increased the yield. Increasing aging time appeared to increase particle size as well as to improve yield, as long as the urea was not depleted. The approximate chemical composition of the precipitate was YOHCO 3 . The YOHCO 3 particles formed were amorphous to X-rays, and underwent a two-stage thermal decomposition, first forming Y 2 O 2 CO 3 near 180°C, and then cubic Y 2 O 3 above 610°C. Generation of CO 3 2− appeared to be crucial to the formation of the solid phase. Heating the aqueous yttrium solution with trichloroacetic acid (CCl 3 COOH) instead of urea as the precipitating agent produced a solid phase, while heating the same solution with formamide (HCONH 2 ) substituted for urea formed no precipitate.

Dynamics of the protein metabolic response to burn injury

Abstract: The protein metabolic response to burn injury was assessed in 17 children aged 7.1 ± 1.1 years (mean ± SEM) and a mean burn size of 65 ± 7% total body surface area (TBSA) during the acute, flow, convalescent, and recovery phases. Stable isotopes of leucine, valine, lysine, and urea were infused in postabsorptive patients in order to measure protein kinetics. The absolute rate of protein breakdown was assessed from the plasma flux of the essential amino acids (EAA), and the rate of urea production (Ra urea) was used as an index of net protein catabolism. Compared to values obtained in recovered patients, the plasma fluxes of all three EAAs were significantly increased ( P P

Effect of Hyperinsulinemia on Urea Pool Size and Substrate Oxidation Rates

Abstract: Recently, indirect calorimetry has frequently been used together with hyperinsulinemic clamps. With few exceptions, however, no attention was paid in these studies to the possible effects of hyperinsulinemia on urea nitrogen ( N ) pool size and the consequences of such changes on the calculated rates of protein, lipid, and carbohydrate (CHO) oxidation. We have determined the effects of euglycemic-hyperinsulinemic clamps on urea N pool size, urinary N excretion, and rates of protein, lipid, and CHO oxidation (measured by indirect calorimetry) in six normal men. Insulin infusion (1 mU · kg −1 · min −1 ) increased peripheral venous insulin concentration from 7 ± 1.2 (mean ± SE) to 51 ±4 μU/ml. Glucose concentration was clamped at 84 ± 1.1 mg/dl. Between 0 (preclamp) and 360 min (end of clamp), blood urea N concentration decreased from 17.2 ± 1.1 to 11 ± 0.8 mg/dl ( P P P

The fate of labelled 15 N urea and ammonium nitrate applied to a winter wheat crop

Abstract: Labelled urea or ammonium nitrate was applied to winter wheat growing on a loamy soil in Northern France. Two applications of fertilizer were given: 50 kg N ha−1 at tillering (early March) and 110 kg N ha−1 at the beginning of stem elongation (mid-April). The kinetics of urea hydrolysis, nitrification of ammonium and the disappearance of inorganic nitrogen were followed at frequent intervals. Inorganic nitrogen soon disappeared, mainly immobilized by soil microflora and absorbed by the crop. Net immobilization of fertilizer N occured at a very similar rate for urea and ammonium nitrate. Maximum immobilization (16 kg N ha1) was found at harvest for the first dressing and at anthesis for the second dressing (23 kg N ha1). During the nitrification period, the labelled ammonium pool was immobilized two to three times faster than the labelled nitrate pool. No significant net15N remineralization was found during the growth cycle. The actual denitrification and volatilization losses were probably more important than indicated from calculations made by extrapolation of fluxes measured over short intervals. However microbial immobilization was the most important of the processes which compete with plant uptake for nitrogen.

Carbamyl Compound Reactions with Ethanol

Abstract: Possible precursors for ethyl carbamate formation in fermented foods and beverages were investigated. It appears that most N-carbamyl compounds will react with ethanol at acid pH levels to form ethyl carbamate. The Arrhenius plots for urea and citrulline were made. The formation is dependent on reactant concentration, temperature, and pH. Components reacted were urea, citrulline, N-carbamyl α-amino acids, N-carbamyl β-amino acid, allantoin, and carbamyl phosphate. A difference between white and red wines on the resulting ethyl carbamate from added urea was noted.

Formation of Ethyl Carbamate Precursors During Grape Juice (Chardonnay) Fermentation. I. Addition of Amino Acids, Urea, and Ammonia: Effects of Fortification on Intracellular and Extracellular Precursors

Abstract: Investigations into the possible precursors for ethyl carbamate with a Chardonnay juice with various additions and treatments indicate significant amounts of precursor can be accounted for by the breakdown of the arginine to form ornithine and urea. This is further substantiated by increases in ornithine, glutamic acid + asparagine, and proline. While it is recognized that citrulline and carbamyl phosphate are also possible reactants, these seemed not to be a significant consideration in these particular experiments. Approximately 40% to 50% of ethyl carbamate precursors could be accounted for by "estimates" of urea at the end of fermentation. In addition to the presence of arginine, it seems that an imbalance in the amino acids and ammonia composition of the juice is required for increased ethyl carbamate precursor formation. The fortification of juice during fermentation changes the amount of ethyl carbamate precursors. Alcohol additions cause a greater percent conversion in the early to middle stages of fermentation when fortification occurs in the presence of yeast than when the yeast is removed. At the latter stages, much less difference occurs. Saccharomyces bayanus (California champagne) produced significantly less ethyl carbamate precursors than did S. cerevisiae (Montrachet) in these experiments.

Ammonia and glutamine metabolism in human liver slices: new aspects on the pathogenesis of hyperammonaemia in chronic liver disease.

Abstract: Ammonia and glutamine metabolism was studied in slices from normal, fatty and cirrhotic human livers. The liver disease was evaluated by histological examination. With respect to ammonia removal, urea and glutamine synthesis in human liver represent low and high affinity systems with k0·5(NH4+) values of 3·6 and 0·11 mM, respectively. Compared with normal control livers, cirrhotic livers showed a decreased glutamine synthesis from NH4Cl by about 80%. The same was true for urea synthesis. Conversely, flux through hepatic glutaminase was increased in cirrhosis 4–6-fold. These changes in hepatic glutamine and ammonia metabolism were observed regardless of whether reference was made to liver wet weight, DNA or protein content. Acetazolamide inhibited urea synthesis in cirrhotic liver slices by about 50%, indicating that mitochondrial carbonic anhydrase is required for urea synthesis also in cirrhosis. There was a significant correlation between the in-vitro determined capacity for urea synthesis from NH4Cl and the in-vivo determined plasma bicarbonate concentration. The data suggest that (i) pathogenesis of hyperammonaemia in chronic liver disease involves the impairment of the perivenous ammonia scavenger cells capable of glutamine synthesis; (ii) the increased flux through glutaminase observed in cirrhosis increases the ammonia input into the urea cycle and acts as a compensatory mechanism for maintenance of a life-compatible urea cycle flux despite the decreased urea cycle enzyme activities; (iii) intramitochondrial bicarbonate provision for carbamoylphosphate synthetase by carbonic anhydrase may become rate-controlling also in liver cirrhosis; and (iv) hyperbicarbonataemia in chronic liver disease may, amongst other effects, be due to an impaired hepatic HCO3- removal by urea synthesis, in line with the concept of a role of the liver in systemic acid–base homeostasis.

The structure of urea—formaldehyde resins

Abstract: Fourier transform infrared (FTIR) spectroscopy has been used as a modern analytical tool to elucidate the structure of urea—formaldehyde (UF) resins. Several low molecular weight condensation products of urea and formaldehyde were synthesized and characterized. Structural differences were observed for prepolymers prepared in alkaline and acidic media. Plausible mechanistic routes are proposed to explain the prepolymer structural differences prepared in different experimental conditions. The structural elucidation of the UF resins is considerably increased and improved by using absorbance magnification to further enhance the observed signals.

Osmotic stability of red cells in renal circulation requires rapid urea transport.

Abstract: Urea transport by the human erythrocyte occurs via an asymmetric-facilitated diffusion system with high Michaelis constants and high maximal velocities; the equivalent permeability in the limit of zero urea concentration is approximately 10(-3) cm/s (J. Gen. Physiol. 81: 221-237, 239-253, 1983). A physiological role for this system is revealed by numerical integration of the appropriate equations that show that rapid urea transport is essential for red cell stability in passing through the renal medulla. The calculation compares two cells. Cell A transports urea with permeability characteristics of normal red cells; cell B has urea permeability similar to lipid bilayers. On entering the hypertonic medulla, both cells shrink, but only B swells on leaving the medulla. The osmotic stress for cell B is greater than for A. Cell B is close to hypertonic hemolysis in the medulla and to hypotonic hemolysis in the cortex. Cell B remains swollen for some time after its exit; the resulting decreased deformability presents a hazard if B reenters the microcirculation. Furthermore, cell B removes a significant fraction of the filtered load of urea and compromises the osmotic gradients in the medulla.

Effects of Dietary Nitrogen Source on Concentrations of Ammonia, Free Amino Acids and Fluorescaminereactive Peptides in the Sheep Rumen

Abstract: Four sheep were fed twice daily a diet of 67% ryegrass hay and 33% concentrate during three, 4-wk periods. The diet was supplemented with one of three N sources: urea, casein or ovalbumin. Urea was the only supplemental N source during Period 1. Sheep were fed either casein or ovalbumin during Period 2, followed by switching of the supplements during Period 3. Statistical comparisons were made only on data obtained during Periods 2 and 3. Ruminal concentrations of NH3, free amino acids and peptides were measured over an 8-h period after feeding. The peptide assay was based on the enhanced fhaorescence of peptides, relative to amino acids, obtained from reaction with fluorescamine at pH 6.2. Ammonia accumulated rapidly to high concentrations (maximum 38 mM at 1 h) after feeding Urea. Ammonia was intermediate with casein and greater (P < .05) than with ovalbumin. Free amino acids were greater (P < .05) with casein (maximum 1.4 mM at 1 h) than with oval- bumin. Free amino acids were intermediate with feeding of urea. Only transient accumulation of peptides occurred when casein was fed: ruminal peptides increased to 3.8 mM at 1 h, but declined to prefeeding levels (.2 mM) by 3 h. Peptides in ruminal fluid from sheep fed ovalbumin were lower (P < .01) and (similar to urea)did not change from prefeeding levels (.2 to .3 raM) throughout the sampling period. It was concluded that slowly degraded proteins, such as ovalbumin, will not give rise to significant peptide levels, whereas rapidly degraded proteins, such as casein, will yield substantial levels of peptides during ruminal protein degradation. (Key Words: Urea, Casein, Egg Albumin, Proteins, Rumen Metabolism, Ammonia, Free Amino Acids, Peptides, Fluorescence.)

Long-term ingestion of ammonium increases acetylglutamate and urea levels without affecting the amount of carbamoyl-phosphate synthase.

Abstract: Rats were fed the following diets: standard (20% protein), high-protein (80%), protein-free, standard plus ammonium and protein-free plus ammonium for six weeks. The standard plus ammonium diet was prepared to contain ammonia equivalent to that supplied by the high-protein diet. Addition of ammonium acetate 20% by mass) to the 20% protein or protein-free diets results in 2.3- and 10-fold increases of urea excretion respectively, without increase of carbamoyl-phosphate synthase. Supplementation of the standard diet with ammonium increases the mitochondrial content of acetylglutamate from 830 to 1590 pmol/mg protein, and of the protein-free diet from 130 to 1040 pmol/mg. However, ingestion of ammonium did not increase the activity of acetylglutamate synthase. Therefore the efflux of acetylglutamate from mitochondria was determined. After 30 min at 37°C liver mitochondria from rats on standard diet released 61% of the initial acetylglutamate while mitochondria from animals on standard plus ammonium diet released only 20%. These results indicate that ingestion of ammonium increases the content of acetylglutamate in rat liver by decreasing its efflux from mitochondria. This effect is similar to that produced in mice by a high protein diet [Morita et al. (1982) J. Biochem. (Tokyo) 91, 563-569]. However while the high-protein diet increases carbamoyl-phosphate synthase content, the ammonium diet does not.

Processes of nitrogen loss from fertilizers applied to flooded rice fields on a calcareous soil in north-central China

Abstract: Losses of nitrogen were investigated after applications of ammonium bicarbonate and urea to flooded rice at transplanting. Ammonia (NH3) volatilization was determined by direct micrometeorological methods, and total loss of fertilizer nitrogen (N) was measured by15N balance. All the loss appeared to be in gaseous forms, since there was no evidence of leaching and runoff was prevented. The difference between N loss and NH3 loss was thus assumed to be denitrification loss. Both NH3 volatilization and denitrification losses were large, being 39% and 33%, respectively, of the ammonium bicarbonate N, and 30% and 33%, respectively, of the urea N applied by farmers' methods. Ammonia fluxes from the field fertilized with ammonium bicarbonate were very high for two days, and then declined rapidly as the NH3 source in the floodwater diminished. Moderate fluxes from the field fertilized with urea continued over 6 days, but calculations showed that NH3 transfer from floodwater to atmosphere was retarded during the middle period of the experiment, particularly on day 2 when a thick algal scum appeared on the water surface. The results indicate that this algal mass obstructed the transport of NH3 across the water-air interface until the scum was dispersed by wind action. Nevertheless, the prolonged NH3 losses on the urea treatment were due primarily to high floodwater pH values promoted by the strong algal growth during the daylight hours. Nitrogen-15 balance studies showed that incorporation of fertilizer into drained soil substantially increased recoveries of fertilizer N in rice plants and soil compared with incorporation of fertilizer in the presence of standing floodwater. Ammonia loss measurements on these treatments when urea was applied suggested that the improvement in fertilizer N efficiency was due mainly to reductions in NH3 loss.

Preparation of Omega‐3 PUFA Concentrates from Fish Oils via Urea Complexation

Abstract: The effect of weight ratio of urea to fatty acids and the urea-fatty acid adduct crystallization temperature on the enrichment of eicosapentaenoic acid from marine oil fatty acids was studied. The optimum ratio of urea to fatty acids was found to be 3 : 1 for laboratory scale preparations and the optimum temperature for the formation of urea-fatty acid adduct was 1°C. At very low temperatures (−12, −18, −35°C) the recovery efficiency for EPA was reduced. Using these optimum values, enrichment of EPA and other n-3 polyunsaturated fatty acids via urea complexation was carried out on a pilot plant scale in a variety of North Atlantic and North Pacific fist oils and a seal oil. Irrespective of hte type of starting oil, all the oils gave a concentrate with 69–85% total n-3 PUFA with an overall yield of 17–20%. Menhaden is clearly an ideal oil for preparation of EPA concentrate, as the starting oil usually has a higher proportion of EPA to DHA than most of the other commercial fish oils.

Methods for the diagnosis of gastrointestinal disorders

Abstract: Methods for the diagnosis of gastrointestinal disorders in human or lower animal subjects comprising the steps of administering to said subject a safe and effective amount of urea and analyzing the breath of said subject for the presence of carbon dioxide or ammonia products of the hydrolysis of said urea, wherein the presence of said hydrolysis products is a positive indication of a gastrointestinal disorder in said subject. Preferably the administered urea contains isotope-labelled nitrogen or carbon.

Elimination of the adverse effects of urea fertilizer on seed germination, seedling growth, and early plant growth in soil

Abstract: The rapidly increasing importance of urea fertilizer in world agriculture has stimulated research to find methods of reducing the problems associated with the use of this fertilizer. One of these problems is that urea has adverse effects on seed germination, seedling growth, and early plant growth in soil. Because there is evidence that these adverse effects are caused largely, if not entirely, by ammonia produced through hydrolysis of urea fertilizer by soil urease, we explored the possibility that they could be reduced or eliminated by amending urea fertilizer with a small amount of a urease inhibitor. Studies with seeds of alfalfa (Medicago sativa L.), barley (Hordeum vulgare L.), oats (Avena sativa L.), rye (Secale cereale L.), sorghum [Sorghum bicolor (L.) Moench], and wheat (Triticum aestivum L.) showed that phenylphosphorodiamidate and N-(n-butyl)thiophosphoric triamide were the most effective of 10 urease inhibitors evaluated for reduction of the adverse effect of urea on seed germination. N-(n-butyl)-thiophosphoric triamide was superior to phenylphosphorodiamidate for reducing the adverse effects of urea solutions on seed germination and seedling growth in soil, and it completely eliminated the adverse effect of urea granules on early plant growth in soil. The data reported indicate that the adverse effects of urea fertilizer on seed germination, seedling growth, and early plant growth in soil could be eliminated or markedly reduced by amending the fertilizer with as little as 0.01% (wt/wt) of N-(n-butyl)thiophosphoric triamide.

Uptake of urea C and urea N by the coastal marine diatom Thalassiosira pseudonana

Abstract: Urea uptake rates of Thalassiusiru pseudonana (clone 3H) were determined using [14C]urea, [15N]urea, and by measuring disappearance of dissolved urea from the medium after adding 10 lg-atoms urea-N liter-‘. In nitrate-sufficient cultures, the average [14C]urea uptake rate was 60% of the urea disappearance rate. Nitrate uptake continued in the presence of urea at a reduced rate, and only 15% of the urea N taken up was retained by the phytoplankton. The increase in PON during incubation was roughly equal to the total NO, and urea N taken up. Average urea uptake rates measured by all methods in 24-h nitrate-starved cultures were in excellent agreement with the rate of increase in PON during a l-h incubation. Uptake rate of [14C]urea and disappearance rate of urea were constant and equal. In neither nitrate-sufficient nor nitrate-starved cultures were [15N]urea uptake rates constant, with maximal rates measured 5.-l 5 min after the addition of urea. Ammonium was released by T. pseudonana following uptake of urea and was then taken up. A model of urea uptake and assimilation by T. pseudonana that involves efflux of urea N as NH, and its rapid reabsorption is proposed. These results can explain previous observations and have implications for utilization and cycling of urea N by phytoplankton in nature.

Conducting polymer-coated enzyme microsensor for urea

Abstract: A microsensor for urea is described which is based on immobilised urease on the tip of a 10 µm diameter ammonia gas electrode made from a polypyrrole film coated on to a platinum wire. The sensor responds rapidly, reaching a steady state within 20–40 s when the concentration of urea in solution is changed from 0.0001 to 0.05 M. The enzymatic response is current limiting. Responses in a wide range of substrate concentrations were achieved (0.001–0.05 M). High storage and operational stability (more than 32 d) have been recorded for the urea microsensor.

Reactions of Ammonia and Urea Hydrolysis Products with Soil

Abstract: The objectives of our study were to compare the rise in soil pH following addition of urea and NH 4 OH to soil, and evaluate the importance of inorganic C reactions to any differences in the rise in pH caused by the two respective N sources. Titration curves with urea of NH 4 OH as a base were used to determine differences in the patterns of pH change. (...) The results demonstrate the importance of inorganic C from urea hydrolysis in providing resistance to a pH increase above pH 8.2 in concentrated fertilizer application zones.

Factors affecting N release of urea from reactive layer coated urea

Abstract: An experimental fertilizer called reactive layer coated urea (RLCU) has been developed by coating urea with a mixture of diisocyanate and polyol in the presence of a catalyst. The hard, durable layer that is formed on the granule conveys slow-release character to the product. A series of soil incubation tests were conducted under simulated upland conditions for periods up to 56 days to study the effect of factors such as temperature, pH, soil moisture, and organic C additions on N release. The N release rate from RLCU was shown to be increased with increasing temperature and decreasing coating thickness. It was unaffected by the addition of lime to raise the pH or organic carbon sources to increase microbial activity. Although a slight effect of soil moisture was noted, it was not pronounced. Urea release tended to be in two stages — a constant diffusive stage in which, it is postulated, urea was still dissolving within the granule and diffusing to the soil at a constant rate and a slower logarithmic stage where the rate of release decreased with time.

Fate of broadcast urea in a flooded soil when treated with N-(n-butyl) thiophosphoric triamide, a urease inhibitor

Abstract: The compound N-(n-butyl) thiophosphoric triamide (NBPT) was found to be a more effective ureas inhibitor than phenyl phosphorodiamidate (PPDA) in flooded soils when compared at concentrations of from 0.5 to 5% of the weight of urea. It allowed essentially no ammoniacal-N to acumulate in the floodwater when added at 0.5% of the weight of urea. The fate of urea was also determined in a flooded, unplanted soil with NBPT used as an inhibitor at a rate of 2% by weight of urea. At 41 days, fertilizer-N loss without the inhibitor was 73.4%, whereas with NBPT, 34.7% of the fertilizer was lost, presumably all by denitrification. With NBPT, urea hydrolysis was not inhibited below a 1 cm depth in the soil and most of the N (35.0%) accumulated as exchangeable NH4+-N. Except for 15.0% of the fertilized accumulated as organic-N on the soil surface layer, immobilized N accounted for only an additional 7.0% in the soil at 22 days. Although the N saved from NH3 volatilization loss obviously is eligible for denitrification losses, denitrification apparently was not enhanced to an appreciable extent by use of the inhibitor in that total losses were 15.7% at 22 days.