Showing papers on "Urea published in 1997"
TL;DR: Blood urea N, body weight, yield of fat-corrected milk, dietary CP content, excess N intake, dry matter intake, and days in milk were positively related to milk ureaN, and parity, milk and fat yield, dietaryCP per unit of NEL content, and NEL intake were negatively related to Milk Urea N.
514 citations
TL;DR: In this article, the effects of thermal annealing on the hydrogen-bonding properties of a poly(urethane urea) copolymer were investigated using FTIR.
Abstract: FTIR was used to investigate the effects of thermal annealing on the hydrogen-bonding properties of a poly(urethane urea) copolymer. The copolymer was based on ethylene oxide-capped poly(propylene oxide) diol, 4,4‘-diphenylmethane diisocyanate (MDI), and 3,5-diethyltoluenediamine (DETDA). The result showed that thermal annealing caused the rise of the number of free urethane groups and the ordering of urea groups. The ordered urea hydrogen bonds were not destroyed below the melting point of the DETDA−MDI hard domain.
300 citations
TL;DR: Excess rumen degradable N in ewe diets elevates urea and ammonia in plasma and in utero, with an associated increase in embryo mortality, Nevertheless, metabolism appears to be up-regulated in some embryos and, among those that survive, fetal growth seems to be enhanced.
237 citations
TL;DR: Low surrounding pH reduces activity of Urease and synthesis of nascent urease, catalase, and presumably of most other proteins, suggesting that H pylori is not acidophilic although it tolerates short-term exposure to low pH.
Abstract: BACKGROUND: Helicobacter pylori produces large amounts of urease presumably to be prepared for the rare event of a sudden acid exposure. The hypothesis that H pylori is acid sensitive and protein production is inhibited by low pH was examined. METHODS: H pylori or its soluble enzymes were incubated buffered or unbuffered at a pH ranging from 2-7 in the presence of 5 mM urea for 30 minutes. After exposure, urease and catalase activities of whole cells, supernatants, and soluble enzyme preparations were measured at pH 6.8. Newly synthesised enzyme was quantified by immunoprecipitation of [35S]-methionine labelled protein. RESULTS: Exposure to buffer below pH 4 resulted in loss of intracellular urease activity. In soluble enzyme preparations and supernatant, no urease activity was measurable after incubation at pH or = 3. Exposure below pH 5 inhibited synthesis of total protein including nascent urease and catalase. At pH 6 or 7, urease represented 10% of total protein, catalase 1.5%. Exposure of H pylori to unbuffered HCl (pH > 2) resulted in an immediate neutralisation; urease and catalase activities and synthesis were unchanged. CONCLUSION: Low surrounding pH reduces activity of urease and synthesis of nascent urease, catalase, and presumably of most other proteins. This suggests that H pylori is not acidophilic although it tolerates short-term exposure to low pH.
221 citations
TL;DR: Regular measurement of milk urea N in bulk samples can be used to monitor N losses from rumen fermentation, however, the value does not give an indication of the efficiency with which the absorbed protein is utilized.
187 citations
Patent•
12 May 1997TL;DR: In this article, Urea is pyrolyzed in a chamber designed to facilitate gasification of the urea by pyrolysizing with conversion of urea to ammonia and isocyanic acid (HNCO) with water vapor and carbon dioxide.
Abstract: Urea is pyrolyzed in a chamber designed to facilitate gasification of the urea by pyrolysis with conversion of urea to ammonia and isocyanic acid (HNCO) with water vapor and carbon dioxide The product gases are introduced into exhaust gases from a lean-burn engine, preferably upstream of a turbocharger The exhaust gases are then contacted with an SCR catalyst
138 citations
TL;DR: A new systematic nomenclature and a new structural model for urea transporters are proposed, which would permit exciting new insights in the future into the mechanisms underlying acute and long-term regulation of urea transport.
Abstract: Physiological and molecular data demonstrate that urea transport in kidney and erythrocytes is regulated by specific urea transporter proteins. The urea transporter in the terminal inner medullary collecting duct permits very high rates of regulated transepithelial urea transport and results in the delivery of large amounts of urea into the deepest portions of the inner medulla, where it is needed to maintain a high interstitial osmolality for concentrating the urine maximally. The urea transporter in erythrocytes permits these cells to lose urea rapidly as they ascend through the ascending vasa recta, thereby preventing loss of urea from the medulla. Urea lost from the medulla would decrease concentrating ability by decreasing the efficiency of countercurrent exchange, as occurs in individuals who lack the Kidd antigen. The recent cloning of cDNAs for these two urea transporters has begun to yield new insights into the mechanisms underlying acute and long-term regulation of urea transport and should permit exciting new insights in the future. This review focuses on the physiological and biophysical evidence that established the concept of urea transporters, the subsequent cloning of cDNAs for urea transporters, and the recent integrative studies into the regulation of urea transport. We also propose a new systematic nomenclature and a new structural model for urea transporters.
135 citations
01 Jan 1997
TL;DR: The diagnostic and interpretive aspects of the various individual fractions of this pool of proteins are the focus of the chapter.
Abstract: Publisher Summary
The nitrogenous compounds of blood plasma encompass all those organic and inorganic nitrogen-containing compounds of blood. These include the organic macromolecular compounds such as the proteins and nucleic acids; the smaller molecular weight compounds such as glutathione, urea, and creatinine; and the inorganic compounds such as nitrate and ammonia. The non-protein nitrogen (NPN) compounds are those grouped together as the fraction of the nitrogen-containing compounds of plasma that are not removed by the common protein precipitating agents such as trichloracetic acid. The principal components of the NPN fraction are urea (50%) and amino acids (25%), which total about 35.7 mmol N/liter (50 mg N/dl) plasma in contrast to protein nitrogen, which totals more than 714 mmol N/liter (1 g N/dl) plasma (or 6.25 g protein/dl). This chapter deals primarily with the latter fraction, which is classed collectively as the plasma or serum proteins. The diagnostic and interpretive aspects of the various individual fractions of this pool of proteins are the focus of the chapter.
124 citations
TL;DR: It was concluded that glucocorticoids can downregulate function and expression of the vasopressin-regulated urea transporter in rat terminal IMCD.
Abstract: This study tested whether glucocorticoids regulate tubular urea transport. Urea permeability was measured in perfused inner medullary collecting duct (IMCD) subsegments from rats that underwent adrenalectomy, adrenalectomy plus replacement with a physiologic dose of glucocorticoid (dexamethasone), or sham operation. Compared with sham rats, basal urea permeability in terminal IMCD was significantly increased in adrenalectomized rats and reduced in dexamethasone-treated rats. Vasopressin significantly increased urea permeability in all three groups. In contrast, there was no difference in basal or vasopressin-stimulated urea permeability in initial IMCD between the three groups. Next, membrane and vesicle fraction proteins were isolated from inner medullary tip or base and Western analysis was performed by use of an antibody to the rat vasopressin-regulated urea transporter. Vasopressin-regulated urea transporter protein was significantly increased in both membrane and vesicle fractions from the inner medullary tip of adrenalectomized rats. There was no change in vasopressin-regulated urea transporter protein in the inner medullary base, and Northern analysis showed no change in urea transporter mRNA abundance in either inner medullary region. It was concluded that glucocorticoids can downregulate function and expression of the vasopressin-regulated urea transporter in rat terminal IMCD.
115 citations
Abstract: A new method of direct immobilization of urease on a hydrated silicon nitride surface with the use of glutaraldehyde is presented. The main parameters characterizing the developed urea biosensor based on pH-ion-selective field effect transistor (pH-ISFET) with directly immobilized urease are: (1) maximal analytical signal, 120–140 mV in 10 mM phosphate buffer solution; (2) linear range of ΔUgs=f(log Curea):pCurea(2–3.5) in 10 mM phosphate buffer; (3) response time, 80 s; and (4) lifetime of 35 days with a stable analytical signal. The biosensor was used for urea determination in blood serum and in hemodialysis fluid with satisfactory results.
111 citations
TL;DR: Low rates of body N loss during dormancy suggested losses of non-urea N as creatinine, and thorough microbial ureolysis and urea-N resorption in winter was indicated.
Abstract: Subadult bears were studied during their autumn hyperphagia (n = 3) and winter dormancy (n = 6) Urea kinetics were measured with 14C- and 15N-urea, protein turnover was estimated with 15N-glycine, and body composition was assessed with 3H-water Reduced amino acid degradation in winter was indicated by declines in plasma urea and aminotransferase activities, and lower urea production than in autumn (47 vs 275 mmol urea-N∙kg−075∙d−1) Only 75% of urea produced in hyperphagic bears was degraded and just 11% of the degraded N reutilized as amino-N Dormant bears reutilized 997% of urea produced, indicating thorough microbial ureolysis and urea-N resorption Low rates of body N loss during dormancy suggested losses of non-urea N as creatinine Protein turnover rates (152–215 g∙kg−075∙d−1) were similar between seasons and reflected the apparent maintenance of hepatic, intestinal, and muscular functions through dormancy Protein synthesis accounted for 32% of energy expended in dormancy, which was ma
TL;DR: The results stress the necessity of Ni for urease activation and thus for the growth of plants on urea-based media.
Abstract: The effect of Ni supply on growth, N metabolism and leaf urease activity of six plant species (rye, wheat, soybean, rape, zucchini and sunflower) grown on urea-based nutrient solutions was investigated. Activity of urease, which is activated by Ni, was hardly detectable in plants of all six species grown without supplementary Ni. As a consequence Ni-deprived plants accumulated considerable amounts of urea, showed a reduced dry matter production and reduced total N concentrations. The lack of urease activation in low-Ni plants made them metabolically N deficient, which is illustrated by the chlorotic appearance of these plants. The soluble amino acid N concentration was reduced by inadequate Ni supply. The amide concentrations (glutamine, asparagine) were considerably affected in all species. The same applied to the concentrations of the urea cycle intermediates arginine, ornithine, and citrulline. These results stress the necessity of Ni for urease activation and thus for the growth of plants on urea-based media.
TL;DR: Regression analysis indicated that the optimal dietary urea level was .5% of DM for ADG and G/F, which increased with intermediate concentrations of urea but decreased with the highest concentration.
Abstract: In Exp. 1, 88 yearling steers (332 kg) were fed dry-rolled corn finishing diets to evaluate effects of dietary urea level on performance and carcass characteristics. Diets contained 0, .5, 1.0, or 1.5% urea (DM basis), which supplied all supplemental N, and 10% chopped prairie hay. Gains (P = .10) and gain efficiency (G/F; P < .05) were increased by .5% urea, with little improvement by additional urea. Regression analysis estimated optimal dietary urea at .9% of DM for ADG and G/F. Fat thickness (P < .05) and yield grade (P < .10) increased linearly with dietary urea level. In Exp. 2, four ruminally and duodenally cannulated steers (557 kg) were fed the diets used in Exp. 1 to evaluate effects of dietary urea on site and extent of digestion. True ruminal OM and starch digestion were increased 25 and 37%, respectively, by .5% urea, but higher urea levels did not differ from .5%. Flows of total N and microbial N to the duodenum were not affected by urea level. In Exp. 3, 100 yearling steers (347 kg) were fed dry-rolled corn finishing diets that contained 10% alfalfa hay as the dietary roughage to evaluate effects of dietary urea level on performance and carcass characteristics. Urea levels were 0, .35, .70, 1.05, or 1.40% urea (DM basis), with no other supplemental N provided. Dry matter intake (P = .10), ADG (P < .05), and G/F (P < .05) increased with intermediate concentrations of urea but decreased with the highest concentration. Regression analysis indicated that the optimal dietary urea level was .5% of DM for ADG and G/F. Urea increased dietary energy utilization but not metabolizable protein supply.
TL;DR: Teleostean fish species of the family Batrachoididae (toadfishes and midshipmen) possess high titers of all enzymes of the ornithine-urea cycle in their livers, and one species in particular, the gulf toadfish, has been shown to rapidly switch from ammonia excretion to urea synthesis and excretion during a variety of stress conditions.
Abstract: Selected teleostean (bony) fish species of the family Batrachoididae (toadfishes and midshipmen) possess high titers of all enzymes of the ornithine-urea cycle in their livers. These species have proven valuable in understanding the short-term regulation of urea synthesis, urea permeability, and transport across epithelial tissues, and how urea synthesis and excretion have evolved among vertebrates. One species in particular, the gulf toadfish (Opsanus beta), has been shown to rapidly switch from ammonia excretion to urea synthesis and excretion during a variety of stress conditions (including confinement). The transition is accompanied by an upregulation of hepatic glutamine synthetase activity, and a switch to pulsatile urea excretion from the anterior end of the fish. In fact, a single day's excretion can be voided in a period of < 3 h. Hypotheses on the environmental significance of these patterns of urea synthesis and excretion are discussed.
TL;DR: In this article, the effects of irrigation, side-dressed application of urea, and urea partially substituted by ammonium sulphate on losses of NH3-N by volatilization in corn crop were evaluated.
Abstract: A field experiment was carried out on a dark-red latosol (Oxisol) of the Centro de Pesquisas Novartis-Seeds, in Uberlândia, State of Minas Gerais, Brazil. The objective of this study was to evaluate the effects of irrigation, side-dressed application of urea, and urea partially substituted by ammonium sulphate on losses of NH3-N by volatilization in corn crop. The fertilizers were applied at 25 and 36 days after planting. The treatments, arranged in randomized complete block design, were: (i) control, (ii) urea, with irrigation before the two applications, (iii) urea, with irrigation after the two applications, (iv) urea + ammonium sulphate (rate N:S = 2.1:1) at the first application, and only urea at the second application, with irrigation before the applications, and (v) with irrigation after applications. Nine samples of volatilized NH3-N were taken, using semi-open static collectors, which were installed after the first N application, at intervals of 4 to 5 days. With irrigation after N application the NH3-N gaseous losses were 40.6% for urea and 23.0% for urea with partial substitution by ammonium sulphate. With irrigation before N application the NH3-N gaseous losses were 42.8 and 38.6%, respectively. Even though the N losses did not show significant differences among the treatments, the partial substitution of urea by ammonium sulphate was positive when the irrigation was performed after the N application. This treatment also showed the largest stalk diameter, the greatest plant high and the highest leaf-N concentration. At harvest, only the fertilized treatments increased yield compared to the control. The relationship between NH3-N volatilized and corn yield established by an inverse linear regression showed that 19.3 kg-1 of grains were lost per every kilogram of volatilized nitrogen.
TL;DR: In this article, the changes in Stokes radius, hydrodynamic volume and partition coefficient that occur when lysozyme is refolded from urea in a size-exclusion column were quantified.
TL;DR: Results indicate that urea pulses are due to activation of an excretion mechanism that rapidly clears urea from the blood plasma, thereby lowering stores throughout the whole body.
Abstract: When subjected to a crowding/confinement protocol in the laboratory, toadfish become facultatively ureotelic, excreting approximately 90 % of their nitrogenous waste as urea-nitrogen (urea-N). The great majority of this excretion occurs via large, irregular pulses from the head region which occur on average once per day, with a duration of 3 h or less. Pulses measured chemically by the appearance of urea-N in the external water were identical to those measured by assaying [14C]urea appearance in the water from the blood plasma. Individual toadfish maintained plasma urea concentrations over widely differing ranges (6600s39 890 mmol-N l-1). However, independent of absolute levels, both [14C]urea and total urea were distributed at ratios close to unity between the blood plasma and the water compartments of liver and white muscle. At times of pulsatile excretion, plasma urea concentration fell sharply. These decreases, distributed throughout the tissues of the whole body, closely matched the sizes of the measured excretion pulses. Between pulses, plasma urea concentration increased steadily at a much slower rate; the rate of rise, when distributed throughout the tissues of the whole body, corresponded to the time-averaged excretion rate over the whole day. Infusion of a typical pulse amount of urea immediately after the end of a natural pulse event raised plasma urea concentration slightly above the pre-pulse level, but did not induce another pulse event. Plasma cortisol levels declined by approximately 60 % over the 4 h period prior to a natural pulse event and then rose quickly again once the pulse had occurred. These results indicate that urea pulses are due to activation of an excretion mechanism that rapidly clears urea from the blood plasma, thereby lowering stores throughout the whole body. Metabolic production of urea is continuous and is not responsible for pulsatile excretion. The pulse event is not triggered by a specific plasma urea threshold, but may involve the hypothalamosinterrenal axis.
TL;DR: It is suggested that in amphibians, solute concentration in the plasma and rate of excretion of urea are coordinated so that at a certain plasma concentration, urea is excreted at the same rate at which it is produced.
TL;DR: In this paper, cyclohexylphosphoric triamide (CHPT) and phenyl phosphorodiamidate (PPDA) were used to control the hydrolysis of urea in duplicate one-liter slurries of cattle and swine wastes.
TL;DR: Helicobacter pylori CPY3401 and an isogenic urease-negative mutant, HPT73, showed chemotactic responses to urea, flurofamide, and sodium bicarbonate, which may be crucial for its colonization and persistence in the stomach.
Abstract: Helicobacter pylori CPY3401 and an isogenic urease-negative mutant, HPT73, showed chemotactic responses to urea, flurofamide (a potent urease inhibitor), and sodium bicarbonate. Since urea and sodium bicarbonate are secreted through the gastric epithelial surface and hydrolysis of urea by urease on the bacterial surface is essential for colonization, the chemotactic response of H. pylori may be crucial for its colonization and persistence in the stomach.
TL;DR: In this article, the authors measured the thermodynamic functions that describe the complexation of a series of carboxylic acid guests and two related quaternary ammonium derivatives with β-cyclodextrin.
Abstract: The thermodynamic functions that describe the complexation of a series of four carboxylic acid guests and two related quaternary ammonium derivatives with β-cyclodextrin were measured using flow calorimetry at 298 K in aqueous media in the presence and in the absence of large concentrations of urea. The relative differences of the thermodynamic parameters of complexation revealed the existence of specific interactions between urea and the aromatic surfaces of some of the nonpolar guests. As expected, the relative changes in the complex stability constants upon addition of urea have been found to depend on the balance of opposing enthalpic and entropic contributions. The interpretation as well as the magnitude of the interaction between urea and aromatic surfaces are in line with previous experimental and computational studies. The experimental evidence presented in this work provides insight into the mechanism by which large amounts of urea denature globular proteins in aqueous media.
TL;DR: In this article, the possibility of using R124 and organic absorbents as working fluids in absorption heat pumps was investigated, and various classes of organic compounds, all commercially available, were tested as absorbents for possible combination with R124; the absorbents included DMAC (N′, N′-dimethylacetamide, C4H9NO), NMP (N-methyl-2-pyrrolidone, C5H 9NO), MCL (Nmethyl ϵ-caprolactam, C7H 13NO), DMEU (dimeth
Abstract: The possibility of using R124 (2-chloro-1,1,1,2,-tetrafluoroethane, CHClFCF3) and organic absorbents as working fluids in absorption heat pumps was investigated. Various classes of organic compounds, all commercially available, were tested as absorbents for possible combination with R124; the absorbents included DMAC (N′, N′-dimethylacetamide, C4H9NO), NMP (N-methyl-2-pyrrolidone, C5H9NO), MCL (N-methyl ϵ-caprolactam, C7H13NO), DMEU (dimethylethylene urea, C5H10N2O), and DMETEG (dimethylether tetraethyleneglycol, C10H22O5). To evaluate the performance of a candidate refrigerant-absorbent pair in a refrigeration or heat pump cycle, the thermophysical properties of the pure components and the mixture and the equilibrium and transport properties have to be determined, either from experimental data or by prediction methods. The thermal stability of the refrigerant-absorbent must also be tested. A method for the calculation of the concentration in the liquid and gas phases and the excess thermodynamic properties of the mixture as a function of the system temperature and pressure based on our experimental setup is described. On the basis of vapor-liquid equilibrium measurements, density and viscosity measurements and thermostability testing, enthalpy-concentration diagrams were constructed. The performance characteristics of the investigated working fluids in terms of the coefficient of performance (COP) and the circulation ratio (f) were calculated for a single-stage absorption cycle. In terms of overall performance (COP, f and stability) R124-DMAC was found to be the superior combination, followed by R124-NMP, R124-DMEU and R124-MCL (the three pairs for which stability problems were found at high temperatures), and finally by R124-DMETEG.
TL;DR: It is concluded that there seems to be little benefit of high protein intake on whole-body protein breakdown and muscle protein synthesis rates in these burn patients, although high-protein diets may enhance wound healing.
Abstract: The response of urea metabolic kinetics, the rate of whole-body protein breakdown, and muscle and skin protein synthesis rates to dietary protein intake (1.15 to 2.92 g/kg/d) was assessed in children with 20% to 40% total body surface area burn injury using a primed continuous infusion of 15 N 2 -urea and l- 13 C 6 -phenylalanine. Plasma urea concentration, production, and excretion rates increased with dietary protein intake without evidence of approaching maximum plateau values. There was no consistent evidence of urea recycling in these subjects (urea production=excretion) at any level of protein intake. The rate of appearance (Ra) of phenylalanine (an index of whole-body protein breakdown) and rate of muscle protein synthesis were independent of dietary protein, whereas there was a significant increase in skin protein synthesis with higher protein intake. We conclude that there seems to be little benefit of high protein intake on whole-body protein breakdown and muscle protein synthesis rates in these burn patients, although high-protein diets may enhance wound healing.
TL;DR: The restricted space allowance resulted in a substantial decrease in daily live-weight gain, and changes in adrenal response and behaviour, and was associated with fewer social interactions and incidence of head-resting behaviour.
Abstract: The objective was to determine the daily live-weight gain, behaviour, adrenal and immune responses of finishing beef heifers housed at two different space allowances. Heifers (no. = 32) with a mean live weight of466 (s.e. 3·6) kg were assigned to either 1·5 or 3·0 m2 average individual space allowance in four slatted-floor pens (two per treatment) for a period of 104 days. On days 5, 40, 68 and 96, heifers (no. = eight per treatment, four per pen) were challenged with 1·98 i.u. ACTH per kg M0·75, and serial blood samples were analysed for plasma cortisol concentrations. The other 16 heifers were immunized against keyhole limpet haemocyanin (KLH) on day 28, and blood samples collected on days 28, 42, 56, 70, 84 and 98 were analysed for anti-KLH immunoglobulin (Ig) concentrations. All heifers were blood sampled on days 0, 14, 56 and 98, and red and white blood cell numbers, packed cell volume (PCV) and plasma concentrations of creatine kinase (CK), non-esterified fatty acids (NEFA) and urea were determined. Behavioural observations were conducted on days 8, 43, 71 and 99 by scan sampling for 24 h (10-min intervals), and continuous 4-h observations were conducted on days 100 and 101.Heifers at 1·5 m2 space allowance had a lower daily live-weight gain compared with those at 3·0 m2 (0·60 v. 0·87 (s.e. 0·04) kg; P 0·05). Heifers at 1·5 m2 had lower plasma NEFA concentrations (P 0·05). The time spent lying down was lower for heifers at 1·5 m2 (10·0 v. 21·1 h/day; P < 0·05). Social interactions were fewer (P < 0·05), and incidence of head-resting behaviour was higher (P < 0·05) among heifers at 1·5 m2 compared with 3·0 m2 space allowance. In conclusion, the restricted space allowance resulted in a substantial decrease in daily live-weight gain, and changes in adrenal response and behaviour.
TL;DR: In this paper, a pulsed-amperometric detection with a polypyrrole-urease biosensor was described for reliable flow injection analysis of urea based on pulsedamperometry.
TL;DR: In this paper, a leaching column study was conducted to evaluate the leaching of urea, ammonium N (NH4•N), and NO3•N forms from selected urea-based controlled-release formulations (Meister, Osmocote, and Poly•S) and uncoated urea under eight cycles of intermittent leaching and dry conditions.
Abstract: Application of soluble forms of nitrogen (N) fertilizers to sandy soils may cause leaching of nitrate N (NO3‐N) resulting in contamination of groundwater. The leaching loss of N may be reduced to a certain extent by the use of controlled‐release N formulations. A leaching column study was conducted to evaluate the leaching of urea, ammonium N (NH4‐N), and NO3‐N forms from selected urea‐based controlled‐release formulations (Meister, Osmocote, and Poly‐S) and uncoated urea under eight cycles of intermittent leaching and dry conditions. Following leaching of 1,760 mL of water (equivalent to 40 cm rainfall) through the soil columns, the recovery of total N (sum of all forms) in the leachate accounted for 28, 12, 6, or 5% of the total N applied as urea, Poly‐S, Meister, and Osmocote, respectively. Loss of urea‐N from all fertilizer sources was pronounced during the initial leaching events (with the exception of Meister). Cumulative leaching of urea‐N was 10% for uncoated urea while <1.7% for the cont...
TL;DR: The pattern of amino acids available from the metabolic pool at zero protein intake is characterized by an imbalance, which can be complemented by exogenous dietary amino acids so that nitrogen excretion may even be smaller than the so-called „obligatory“ losses of intakes not exceeding requirement.
Abstract: Urea and plasma protein differ in natural15N abundance up to 10‰ The origin of this difference is the branched nitrogen metabolism in the liver. One main branch is the protein synthesis pathway, the other the urea synthesis pathway. By this branching15N of precursor amino acids is depleted in urea while it is enriched in protein. With the15N abundance of precursor amino acids, which may be taken from jejunum tissue, utilization of amino acids in liver metabolism can be calculated from isotope discrimination in either pathway. This was investigated by feeding different proteins to rats. When feeding high quality protein (whey protein) utilization of amino acids in liver metabolism at requirement intake was better than at zero protein intake (>85% vs. 70%). From this we conclude that the pattern of amino acids available from the metabolic pool at zero protein intake is characterized by an imbalance. This endogenous imbalance can be complemented by exogenous dietary amino acids so that nitrogen excretion may even be smaller than the so-called „obligatory“ losses of intakes not exceeding requirement. Thus, the quality of dietary protein is reflected not only by N balance. It also may be quantified by analysis of isotope discrimination in nitrogen metabolism of the liver. In addition, the quality of amino acid pattern available from the metabolic pool is indicated by this method.
TL;DR: The change of the enzyme activity coincided with that of the rate of ANS binding during denaturation by low concentration of denaturant, suggesting that the activation of AK by denaturants may be due to the increasing conformational flexibility at its active site.
TL;DR: In this paper, the best catalytic activity was shown by [Ru(CO)3I3]NBu4 catalyst and the effect of solvents, temperature, aniline and promoter concentration on the activity and selectivity of this catalyst was studied.
Abstract: Oxidative carbonylation of aniline to N,N′diphenyl urea was achieved at 100°C and atmospheric pressure conditions. The screening of several homogeneous transition metal complexes was carried out. The best catalytic activity was shown by [Ru(CO)3I3]NBu4 catalyst. The effect of solvents, temperature, aniline and promoter concentration etc. on the activity and selectivity of this catalyst was studied. The activation energy of the reaction is evaluated as 26.6 kcal/mol. A plausible mechanistic pathway for oxidative carbonylation of aniline to diphenyl urea has also been proposed.
TL;DR: It is suggested that urea may be an important source of nitrogen often found inside the tank of V. philippocoburgii, while urea and NH 4 + shifted this ratio in favour of cytokinins, thus apparently inhibiting root development in both species.
Abstract: The long-term effects of different nitrogen sources on the endogenous IAA and cytokinin levels in two bromeliad species were investigated. In nature, Vriesea philippocoburgii is a tank-forming epiphytic bromeliad which uses the tank water reservoir as a substitute for soil, whereas Tillandsia pohliana is a tankless atmospheric epiphytic species. A culture was established from seeds germinated in aseptic condictions, and the plantlets were grown for 6 months in a modified Knudson medium to which was added 8 mol m -3 of nitrogen in the form of NO 3 - NH4 + or urea. The hormonal contents of the bromeliad shoots were determined by means of high-performance liquid chromatography (HPLC), coupled to an enzyme-linked immunosorbent assay (ELISA) for indole-3-acetic acid (IAA), isopentenyladenine (iP), isopentenyladenosine ([9R]iP), zeatin (Z) and zeatin riboside ([9R]Z). Nitrogen supplied in the form of urea gave the highest values of fresh and dry weights for both species, and this was positively correlated to IAA levels. The cytokinin patterns showed that isopentenyladenosine was the predominant form for both species in all samples. However, urea induced the highest level of this riboside form and also the highest level of total cytokinins for V. philippocoburgii, while NH 4 + had the same effect on the atmospheric species. These results are discussed in terms of the different growth habits of these two species in nature. It is suggested that urea may be an important source of nitrogen often found inside the tank of V. philippocoburgii. NO 3 - treatment increased the IAA/Cks balance, mainly for V. philippocoburgii, while urea and NH 4 + shifted this ratio in favour of cytokinins, thus apparently inhibiting root development in both species.