Showing papers on "Urea published in 1976"
TL;DR: Effects of amino acids upon microbial growth, optimum ratio of nonprotein to amino acid nitrogen for microbialgrowth, and incorporation of amino acid into microbial cells were determined with washed cell suspension in vitro as were rumen microbial cells.
180 citations
Patent•
03 Mar 1976TL;DR: In this article, a method for reducing NO x in combustion effluents comprising introducing urea at elevated temperatures in the presence of oxygen, either as a solid or solution in amounts sufficient to reduce the NO x concentration was presented.
Abstract: Method for reducing NO x in combustion effluents comprising introducing urea at elevated temperatures in the presence of oxygen, either as a solid or solution in amounts sufficient to reduce the NO x concentration. Conveniently, the urea may be introduced as a solid powder or as a solution in a hydroxylic solvent, at temperatures in excess of 1300° F. and in the presence of at least 0.1 volume percent oxygen. This invention was made under contract with or supported by the Electric Power Research Institute.
153 citations
TL;DR: Rates of flux through, and transfer of N between these and other nitrogenous pools in the body were calculated by solving this model and the information derived has been applied to whole-animal models with a view to subsequently using these models in computer simulation studies.
Abstract: 1. A study of ammonia and urea metabolism in sheep was made using isotope dilution techniques with (15NH4)2SO4,[15N]urea and [14C]urea in order to determine quantitatively the movements of urea-N and NH3-N throughout the body of normal, feeding sheep. 2. Single injections of 15N-labelled compounds were made into the rumen fluid NH3, caecal fluid NH3 and the blood urea pools, in order to estimate the rates of flux through, and the transfer of N between, these and other nitrogenous pools in the body. 51CrEDTA was injected into the rumen and caecum with (15NH4)2SO4 to allow estimation of fluid volumes and to provide an indication of mixing, and of times of transit of isotopes between different sampling sites in the digestive tract. 3. The sheep ate approximately 22 g lucerne chaff/h and the mean dietary N intake was 16-3 g/d. 4. The rate of flux of NH3 through the rumen NH3 pool was 15-0 g/d (i.e. 90% of the dietary N ingested; however, this amount also included N from plasma urea (1-1 g/d) and other endogenous sources including NH3 derived from caecal NH3 (0-4 g/d). 5. Only 40% of the N in isolated rumen bacteria was derived from NH3, indicating that a considerable proportion of their N requirements were obtained from compounds other than NH3 (e.g. peptides and amino acids). 6. There was evidence of recycling of N between nitrogenous pools in the rumen, probably through rumen NH3 leads to microbial N leads to NH3. 7. It was estimated that 5-3 g blood urea-N/d entered the digestive tract; 20% of this urea was degraded in the rumen, 25% in the caecum and the remainder was apparently degraded elsewhere; there was evidence of urea degradation in the large intestine posterior to the caecum and it is suggested that urea degradation and absorption of the resultant NH3 may occur in the ileum. 8. Of the 4-8 g N/d entering the caecal NH3 pool, 4-2 g N/d left and did not return and the difference (0-6 g N/d) was recycled, possibly through caecal NH3 leads to microbial N leads to NH3. 9. A large proportion of the NH3 entering the caecal NH3 pool (70% or 3-2 g N/d) was apparently derived from degradation of nitrogenous products, other than urea, including rumen microbial N (1-0 g N/d) passing undigested from the small intestine. 10. Less than half the NH3-N of caecal origin entering the rumen passed through the blood urea pool; the remainder was apparently transported as other nitrogenous compounds in the blood or body fluids. 11. The results of the three experiments were combined in a general three-pool, open-compartment model which formally recognizes an unlimited number of other unspecified, interconnected pools together comprising the whole-animal system. Rates of flux through, and transfer of N between these and other nitrogenous pools in the body were calculated by solving this model and the information derived has been applied to whole-animal models with a view to subsequently using these models in computer simulation studies.
134 citations
TL;DR: Small amounts of amino acids to a diet containing urea as the sole nitrogen source improved considerably rumen microbial protein yields and rates of microbial growth, volatile fatty acid production, and effects of amino acid additions upon microbial nitrogen yields were highest right after feeding and decreased with time after feeding.
116 citations
TL;DR: Changes in serum urea, alpha-amino nitrogen and free tyrosine determined before and after physical exercise of different duration strongly suggest an increased breakdown of nitrogen-containing compounds during prolonged exercise.
Abstract: In eight groups of healthy male athlets, aged 19-44 years, serum urea, alpha-amino nitrogen and free tyrosine were determined before and after physical exercise of different duration. Exercise was competitional running, skiing, march or bicycle ergometer work, its duration between 15 and 765 min. The results were compared with previous data from this laboratory and those of other authors. After about 60-70 min of exertion, there is a significant fall in serum amino nitrogen and a rise in urea and free tyrosine; the magnitude of these changes correlated well to the duration of exercise. Likewise, there is a significant correlation between increase in serum urea and decrease in amino nitrogen. The observed changes strongly suggest an increased breakdown of nitrogen-containing compounds during prolonged exercise.
113 citations
TL;DR: The rate at which isolated rat liver mitochondria synthesized citrulline with NH4C1 as nitrogen source was markedly dependent on the protein content of the diet, consistent with the postulate that when NH4Cl plus ornithine are present in an excess, the rate of urea synthesis is regulated at the level of carbamoyl phosphate synthase activity.
Abstract: The rate at which isolated rat liver mitochondria synthesized citrulline with NH4C1 as nitrogen source was markedly dependent on the protein content of the diet. 2. Citrulline synthesis was not rate-limited by substrate concentration, substrate transport or ornithine transcarbamoylase activity under the conditions used. 3. The intramitochondrial content of an activator of carbamoyl phosphate synthase, assumed to be N-acetyl-glutamate, varied markedly with dietary protein content. The variation in the concentration of this activator was sufficient to account for the observed variation in the rates of citrulline synthesis if this synthesis were rate-limited by the activity of carbamoyl phosphate synthase. 4. The rates of urea formation from NH4Cl as nitrogen source in isolated liver cells showed variations in response to diet that closely paralleled the variations in the rates of citrulline synthesis observed in isolated mitochondria. 5. These results are consistent with the postulate that when NH4Cl plus ornithine are present in an excess, the rate of urea synthesis is regulated at the level of carbamoyl phosphate synthase activity.
102 citations
TL;DR: Conformational changes of apo A-1, the principal apoprotein of human plasma high density lipoprotein, have been studied by differential scanning calorimetry and ultraviolet difference spectroscopy as a function of temperature, pH, concentration of apop protein, and urea concentration.
97 citations
TL;DR: The proteolytic activity of rat liver chromatin in salt and urea was found to be independent of the methods of chromatin preparation and may be useful to researchers interested in purifying various chromosomal proteins or to those researchers doing reconstitution studies with labile chromatins.
Abstract: A chromatin-bound protease, active in 2 M NaCl-5 M urea or 5 M urea alone, was demonstrated in rat liver, kidney, testes, brain, rabbit bone marrow, chicken reticulocyte, and Ehrlich ascites chromatin. Chicken erythrocyte chromatin did not possess any detectable proteolytic activity in salt and urea. The proteolytic activity of rat liver chromatin in salt and urea was found to be independent of the methods of chromatin preparation. The protease can be inhibited by the serine specific reagents phenylmethanesulfonyl fluoride and diisopropyl fluorophosphate and the alkylating reagent, carbobenzoxyphenylalanine chloromethyl ketone, in the presence of organic solvents at 1 mM concentration. The inhibitions of chromatin-bound protease in rat liver by these compounds are irreversible. On the other hand, carbobenzoxyphenylalanine and p-nitrophenyl acetate were shown to be reversible inhibitors of rat liver chromatin-bound protease. The application of these inhibitors during the dissociation of chromatin by salt and urea may be useful to researchers interested in purifying various chromosomal proteins or to those researchers doing reconstitution studies with labile chromatins.
95 citations
TL;DR: The densities and heat capacities per unit volume of the symmetrical tetraalkylammonium bromides (R4NBr) were measured in H2O, D2O and 3 m aqueous urea from 0.01 to 1 mol kg−1 and from 5 to 55 °C.
Abstract: The densities and heat capacities per unit volume of the symmetrical tetraalkylammonium bromides (R4NBr) were measured in H2O, D2O, and 3 m aqueous urea from 0.01 to 1 mol kg−1 and from 5 to 55 °C ...
86 citations
TL;DR: In this article, the basic subunits of the 11S globulin molecule were found to be present in equimolar amounts in the SDS gel and the molecular weight consideration, and disulfide bonds appeared to participate in the binding between the acidic and basic subunit in the molar ratio of 1: 1 with the following combi...
Abstract: The acidic and the basic subunits were shown to be present in equimolar amounts in the 11S globulin molecule by the densitometric scanning of the SDS gel and the molecular weight consideration. The four acidic subunits (A1, A2, A3 and A4) were found to be present in the approximate molar ratio of 1:1:2:2. Four basic subunits separated and designated as B1, B2, B3 and B4 based on the relative mobilities in the acidic gel in 7 m urea were found to be present in the approximate molar ratio of 1:1:2:2. The four basic subunits were fractionated in approximately same amounts into three different peaks, peak I (B1 and B2), peak II (B3) and peak III (B4) by CM-Sephadex C–50 column chromatography in the presence of 6 m urea. Three kinds of intermediary subunits of 11S globulin were fractionated with DEAE-Sephadex A–50 in the absence of reducing agents in 6 m urea, and disulfide bonds appeared to participate in the binding between the acidic and the basic subunits in the molar ratio of 1: 1 with the following combi...
79 citations
TL;DR: Maximum net microbial production can be obtained when the diet supplies an amount of fermentable N equal to the microbial N output as digestible OM content increases from 400 to 800 g/kg DM.
Abstract: 1. Plasma urea entry rate, urinary area excretion and, by difference, urea recycling in the body, together with the flow of non-ammonia N through the abomasum and digestion of dry matter (DM) before the abomasum were determined in both wethers and lambs receiving cereal-starch diets supplemented with urea to give 60-120 g crude protein (N X 6-25)/kg DM. 2. Lambs excreted less urea in urine than wethers given the same diet. 3. Relationships between plasma urea entry rate or urine urea excretion rate and plasma urea concentration were different for lambs compared to wethers suggesting greater conservation of body N by renal control in lambs. 4. Recycling of urea was not related to plasma urea concentration in wethers but was related exponentially in lambs, suggesting recycling is controlled rather than the result of simple diffusion from the blood to the gastro-intestinal tract. 5. Abomasal non-ammonia-N flow was similar for wethers and lambs and increased linearly with urea supplementation. 6. DM digestion prior to the abomasum was not significantly altered, although there was a tendency for decreased digestion of the basal diet given to lambs. 7. Maximum microbial N flow to the abomasum was estimated as 30 g N/kg organic matter (OM) fermented in the rumen. 8. This work and the literature reviewed suggested maximum net microbial production can be obtained when the diet supplies an amount of fermentable N equal to the microbial N output. It is calculated the diet should supply approximately 26 g fermentable N/kg digestible OM or 1-8 g fermentable N/MJ metabolizable energy. This corresponds to a fermentable crude protein supply varying from 65 to 130 g/kg DM as digestible OM content increases from 400 to 800 g/kg DM.
TL;DR: Rumen microbial dry matter, nitrogen, ribonucleic acid, deoxyribonucleous acid, glucose disappearance, and production of volatile fatty acids were considerably higher in medium containing urea plus amino acids as compared with urea only.
TL;DR: The data suggest that urea is actively secreted by the straight segments of both the superficial and juxtamedullary proximal tubules of rabbit proximal Tubules, which may contribute significantly to the high urea concentration found at the bend of Henle's loop by micropuncture.
Abstract: Studies utilizing in vitro microperfusion were designed to examine whether urea is actively or passively transported across superficial and juxtamedullary straight segments of rabbit proximal tubules. With perfusate and bath solutions containing 1 mM urea and electrolytes similar to normal plasma, the efflux (lumen-to-bath) isotopic permeability (X 10(-5) cm s-1) of superficial segments was 1.37 +/- 0.16 and of juxtamedullary segments was 2.14 +/- 0.20. In the same tubules, the influx (bath-to-lumen) isotopic permeability was 3.70 +/- 0.35 in superficial segments and 4.75 +/- 0.37 in juxtamedullary segments. Despite net water movement in the opposite direction (0.5 nl mm-1 min-1), the influx rate was significantly higher than the efflux rate of urea in both groups. With a low perfusion rate (2 nl/min) and equivalent specific activities of [14C]urea in bath and perfusate, the collected-to-perfused ratio of [14C]urea, corrected for volume marker change, was 1.07 +/- 0.01 in superficial and 1.09 +/- 0.01 in juxtamedullary nephrons, thus indicating net secretion in both segments. In separate studies urea influx was inhibited by hypothermia (decrease from 37 degrees to 28 degrees C), by phloretin (0.1 mM in bath), by cyanide (1 mM), but not by probenecid (0.2 mM). In each case the inhibition was highly significant and reversible. These data suggest that urea is actively secreted by the straight segments of both the superficial and juxtamedullary proximal tubules. These segments may, therefore, contribute significantly to the high urea concentration found at the bend of Henle's loop by micropuncture.
TL;DR: The restrictive conditions of urea assimilation were examined as possible bases for selection schemes to recover urease-overproducing mutants and it appears likely that methylammonia inhibits urea utilization in cultured soybean cells primarily due to its "repressive" effect on urea synthesis.
Abstract: Cultured soybean (Glycine max, Kanrich variety) cells grow with 25 mm urea as the sole nitrogen source but at a slower rate than with the Murashige and Skoog (MS) (Physiol. Plant. 15: 473-497, 1962) nitrogen source of 18.8 mm KNO(3) and 20.6 mm NH(4)NO(3). Growth with urea is restricted by 18.8 mm NO(3) (-), 50 mm methylammonia, 10 mm citrate or 100 mum hydroxyurea, substances which are much less restrictive or nonrestrictive in the presence of ammonia nitrogen source. The restrictive conditions of urea assimilation were examined as possible bases for selection schemes to recover urease-overproducing mutants. Since urease has higher methionine levels than the soybean seed proteins among which it is found, such selections may be a model for improving seed protein quality by plant cell culture techniques.Callus will not grow with 1 mm urea plus 18.8 mm KNO(3). Urease levels decrease 80% within two divisions after transfer from MS nitrogen source to 1 mm urea plus 18.8 mm KNO(3). Hydroxyurea is a potent inhibitor of soybean urease and this appears to be the basis for its inhibition of urea utilization by callus cells.Stationary phase suspension cultures grown with MS nitrogen source exhibit trace or zero urease levels. Soon after transfer to fresh medium (24 hours after escape from lag), urease levels increase in the presence of both MS or urea nitrogen source. However, the increase is 10 to 20 times greater in the presence of urea. NH(4)Cl (50 mm) lowers urease induction by 50% whereas 50 mm methylammonium chloride results in more drastic reductions in urea-stimulated urease levels. Citrate (10 mm) completely blocks urease synthesis in the presence of urea.Ammonia and methylammonia do not inhibit soybean urease nor do they appreciably inhibit urea uptake by suspension cultures. It appears likely that methylammonia inhibits urea utilization in cultured soybean cells primarily due to its "repressive" effect on urease synthesis.Citrate does not inhibit urease activity in vitro and exhibits only a partial inhibition (0-50% in several experiments) of urea uptake. It appears likely that the citrate elimination of urease production by cultured soybean cells is due to its chelation of trace Ni(2+) in the growth medium. Dixon et al. (J. Am. Chem. Soc. 97: 4131-4133, 1975) have reported that jack bean (Canavalia ensiformis) urease contains nickel at the active site.
TL;DR: In this article, a procedure is described that allows assay of soil urease activity using a phosphate buffer (pH 8.8) and a urea substrate concentration of 0.007 M. The method is precise, and compares favourably with other procedures.
Abstract: A procedure is described that allows assay of soil urease activity. The method uses a phosphate buffer (pH 8.8) and a urea substrate concentration of 0.007 M. Incubation for 4 h at 37°C is recommended and urease activity is estimated by determining the amount of ammonium produced by urea hydrolysis in soil. The method is precise, and compares favourably with other procedures. re]19750710
TL;DR: The data suggest that inhibition of protein synthesis provides an increased availability of intra-cellular amino acids and that many of these are rapidly degraded, yielding urea and glucose, supported by the fact that intracellular alanine levels were significantly increased following cycloheximide treatment.
TL;DR: Bacterial generation of organic solute in faeces which have left the body is sufficiently rapid to cast serious doubts on the validity of faecal centrifugation, or other time-consuming techniques involving lengthy handling of faes, as methods of obtaining extracellular faecic fluid for measurements of organic constituents or ammonia.
Abstract: 1. A 25% faecal suspension in sodium chloride solution, incubated anaerobically at 37 degrees C for 48 h, showed excellent survival of all the main groups of faecal bacteria. 2. All faecal incubation systems studied generated large amounts of ammonia, particularly those in which bacterial counts fell during incubation. As normal faeces contain negligible amounts of urea this ammonia must have been generated from sources other than urea. 3. Ammonia was also generated by faeces delivered by sodium chloride enema, and by ileostomy fluid, indicating that the phenomenon is not confined to distal colonic contents. 4. Ammonia generation by incubated faeces was inhibited by prior autoclaving of the sample, but not by sterilization with gamma-irradiation. 5. Generation of ammonia by incubated stool was accompanied by release of large amounts of organic anion and a fall in pH. 6. These observations are interpreted as evidence that ammonia generated within the colon in situ is not derived exclusively from urea, but also from bacterial deamination of amino acids, peptides and proteins. Simultaneously bacterial activity generates large amounts of organacid. The presence of living bacteria is not essential for ammonia generation, provided that bacterial enzymes are present. 7. Bacterial generation of organic solute in faeces which have left the body is sufficiently rapid to cast serious doubts on the validity of faecal centrifugation, or other time-consuming techniques involving lengthy handling of faeces, as methods of obtaining extracellular faecal fluid for measurements of organic constituents or ammonia.
TL;DR: The conversion of urea to ammonia is quantitative for sample concentrations of less than 0.03 M and the response is independent of variations in the flow rate, enzyme activity or temperature of the reactor.
TL;DR: Comparison of ethanolic cell extracts with extracts from plant organs shows that although these compounds are present in parts of the plant they are not the major phenolics, indicating an antagonism between tannin synthesis and nitrogen metabolism.
Abstract: Phenolic metabolism is influenced by the levels of sucrose, nitrogen and 2,4 dichlorophenoxyacetic acid (2,4-D) in the growth medium. Chromatographic evidence suggests that the principle products are polymers of leucocyanin, (-) epicatechin and (+) catechin, constituting condensed tannins. Comparison of ethanolic cell extracts with extracts from plant organs shows that although these compounds are present in parts of the plant they are not the major phenolics. Cells maintained in a modified Heller's medium containing 9.0×10−7 M 2,4-D produce increased levels of tannins from mid passage (day 12) onwards. The presence of 2,4-D at 9.0×10−6 M supresses this response and increased initial sucrose levels cause the amount of tannins to be greater. At the period when tannin levels increase the standard medium is exhaused of its nitrogen sources, urea and nitrate. Increased initial nitrogen levels delay the beginning of increased tannin production and the addition of urea or 2,4-D to cultures already containing high levels of tannins causes the tannin content per gram fresh weight and per culture to decline. These results indicate an antagonism between tannin synthesis and nitrogen metabolism. The activity of phenylalanine ammonia-lyase EC 4.1.1.5. (PAL) estimated by a spectrophotometric method in acetone powders derived from Acer cells increases three to four fold at the onset of increased tannin synthesis and then declines sharply. The phase of high PAL activity correlates with the exhausion of the medium nitrogen sources.
TL;DR: It was concluded that intermediates provided by both ornithine and lactate are limiting for urea production from ammonia in isolated liver cells, and it was suggested that the stimulatory effect of lactate lies in increased availability of cytosolic aspartate for condensation with citrulline.
Abstract: 1. In hepatocytes isolated from 24 h-starved rats, urea production from ammonia was stimulated by addition of lactate, in both the presence and the absence of ornithine. The relationship of lactate concentration to the rate of urea synthesis was hyperbolic. 2. Other glucose precursors also stimulated urea production to varying degrees, but none more than lactate. Added oleate and butyrate did not stimulate urea synthesis. 3. Citrulline accumulation was largely dependent on ornithine concentration. As ornithine was increased from 0 to 40 mM, the rate of citrulline accumulation increased hyperbolically, and was half-maximal when ornithine was 8-12 mM. 4. The rate of citrulline accumulation was independent of the presence of lactate, but with pyruvate the rate increased. 5. The rate of urea production continued to increase as ornithine was varied from 0 to 40 mM. 6. It was concluded that intermediates provided by both ornithine and lactate are limiting for urea production from ammonia in isolated liver cells. It was suggested that the stimulatory effect of lactate lies in increased availability of cytosolic aspartate for condensation with citrulline.
TL;DR: In this paper, a study was designed to evaluate these methods of reducing N losses by measuring yield and recovery of applied N by potato (Solanum tuberosum L) tubers and corn (Zea mays L) grain Supplemental N treatments applied each year for 3 years were as follows: urea in a single or split application, SCU impregnated with a wax coating, and SCU with only a sulfur coating.
Abstract: Excessive rates of soluble N fertilizers are sometimes used on irrigated sands in Central Wisconsin to compensate for loss of some of the applied N by leaching Use of a slow-release form of N or several small applications of a soluble N fertilizer may eliminate some leaching and subsequent loss of NO₃-N This study was designed to evaluate these methods of reducing N losses by measuring yield and recovery of applied N by potato (Solanum tuberosum L) tubers and corn (Zea mays L) grain Supplemental N treatments applied each year for 3 years were as follows: 1) urea in a single or split application, 2) SCU impregnated with a wax coating, and 3) SCU with only a sulfur coating Recovery of applied N by tubers from a single urea application was extremely low in 1972 due to severe leaching induced by abnormally high precipitation Slow-release SCU carriers produced higher yields and N recovery that year because their slow dissolution reduced leaching losses of N However tuber yields and recovery of N from urea treatments were greater than from SCU treatments in 1973 and 1974 because of reduced leaching those years In addition, the supplemental N (urea or SCU) for all potato treatments was protected from leaching in 1973 and 1974 by placement of the N into a relatively dry zone of the potato hill Corn yields and grain N recovery were similar among carriers of N in 1972 and higher from urea than SCU in 1973 and 1974 The greater recovery of N from urea by corn grain as compared to potato tubers in 1972 apparently was due to the deeper rooting of corn Furthermore the potatoes received twice as much water by irrigation as compared to the corn Oat (Avena sativa L) forage yields from both trials in 1975 indicated there was greater residual N in SCU plots than urea plots due to incomplete release of urea-N from SCU Adequate dissolution of SCU-N within a single growing season occurred only under severe N-leaching conditions
TL;DR: In this article, the effect of three organophosphorus insecticides on soil urease was examined, and it was suggested that the application of insecticides to control soil-borne insect pests may be a factor in determining the efficiency of urea fertilizer mineralization.
Abstract: The effect of three organophosphorus insecticides on soil urease was examined. Inhibition of urea hydrolysis, some 60 days after application of 1000 parts/106 of insecticide to a sandy clay loam, approached 40% (accothion) and exceeded 50% in the case of malathion and thimet. Similar inhibitory effects were recorded using a silt loam soil with which 200 parts/106 application also produced inhibition ranging from 14% (accothion) to 23% (thimet) after 10 days. With lower concentrations of insecticide (50 parts/106) inhibition, though again significant, was of a more ephemeral nature. All three insecticides, at a concentration of 1000 parts/10+6, prevented almost any hydrolysis of urea by jack bean urease. Ureolytic microorganisms, isolated from the soils under investigation, were inhibited by the organophosphates to a greater or lesser extent but the development of tolerance was common. It is suggested that the application of insecticides to control soil-borne insect pests may be a factor in determining the efficiency of urea fertilizer mineralization.
TL;DR: A recirculating ion exchange system was designed in which a cation exchange resin (Amberlite IRC 50) was used to control the pH of solutions in which soybeans were grown as discussed by the authors.
Abstract: Growth and nodulation response of soybean (Glycine max (L.) Merr.) to various single nitrogen sources in solution culture is confounded by unequal shifts in solution pH. A recirculating ion exchange system was designed in which a cation exchange resin (Amberlite IRC 50) was used to control the pH of solutions in which soybeans were grown. Nutrient solution pH levels were established at range extremes of 9.0 to 3.7 with 100% Ca2+ or H+ forms of resin, respectively. Intermediate pH levels were established by varying the ratio of Ca2+ to H+ forms of resin. The system is capable of maintaining pH within 0.5 to 0.9 units of the initial pH over a two-week growth period of soybeans with either nitrate- or urea-N sources. In the absence of the resin column, pH of the urea nutrient solution rapidly declined to less than pH 4 which resulted in depressed plant nodule development. The optimum pH range for nodule mass and N2 fixation (measured by acetylene reduction) was between 5.2 and 7.0 with urea nutrition. Both nitrate- and ammonium-N sources were inhibitory to acetylene reduction in comparison with urea which allowed extensive nodule development and activity.
TL;DR: Evidence is brought to evidence that the relative contribution of water abstraction and solute addition to the concentrating process along the thin descending limb can vary in a given species as a function of the physiological state.
Abstract: Micropunctures were performed at the tip of Henle's loops and vasa recta accessible at the extrarenal surface of the papilla in a desert rodent (Psammomys obesus) studied under mild NaCl (NaCl 4%, 0.0375 ml/min) and mild urea (urea 4%, 0.0375 ml/min) loading conditions. In NaCl loaded animals, it was confirmed that solute addition (mainly sodium) contributes in a large proportion to the concentrating process along the thin descending limb. Comparison of sodium and urea concentrations in the loops with those in vasa recta at the same level of the papilla demonstrated that 1. the transepithelial sodium gradient was compatible with a diffusion transport of this ion from the interstitium to the thin descending limb; 2. the sodium concentration higher in interstitium than in the loop fluid was not compatible with the existence of a purely passive concentrating process in inner medulla as was recently proposed [8], 3. the transepithelial urea gradient was very limited which indicates that this solute does not play an important part in the concentrating process. In urea loaded psammomys, solute addition (mainly urea) to the thin descending limb fluid was still present but water abstraction was enhanced as compared to salt loaded animals, probably on account to the higher interstitial urea concentration. It is, thus, brought to evidence that the relative contribution of water abstraction and solute addition to the concentrating process along the thin descending limb can vary in a given species as a function of the physiological state.
TL;DR: A central composite design with protein 9.4 to 16.2% and urea 0 to 40% of nitrogen, all expressed as dry matter, was the basis for nine rations to which 36 cows were allotted equally as discussed by the authors.
TL;DR: Dimeric albumin was found to support growth of lymphocytes as well as monomeric albumin, and mercaptalbumin and non-mercaptalbumin were shown to have equal activity.
TL;DR: Aroylphenylacetylenes (I) reacted with ethyl and phenyl hydrazinecarboxylates (II) to give ω-aroylacetophenone-N-ethoxy carbonyl-(Vla-f) and N-phenoxycarbonyl--(VIg-l) hydrazones, respectively.
TL;DR: The respiration rates of microflora of layers of soil-surface organic horizon of a black spruce stand have been studied manometrically under controlled conditions of moisture, temperature, and aeration in the presence of urea and other nitrogen and mineral amendments.
Abstract: The respiration rates of microflora of layers of soil-surface organic horizon of a black spruce (Picea mariana (Mill.) B.S.P.) stand have been studied manometrically under controlled conditions of moisture, temperature, and aeration in the presence of urea and other nitrogen and mineral amendments. L.F., and F2 samples from field plots fertilized with 448 kg N/ha as urea in 1961 had still in 1971 greater respiration rates than similar samples from unfertilized field plots. In lab tests, addition of urea (112, 280, and 448 kg N/ha or 875, 2187, and 3500 ppm N) stimulated the endogenous respiration of each layer. The stimulation was greater when 2187 ppm N was applied and when moisture and temperature of the layers were maintained at 60% water-holding capacity and 20 degrees C during the 42-day incubation period. Addition of Mg, Ca, and K to urea-fertilized layers increased respiration while P and S decreased it. Addition of NH4NO3 and (NH4)2SO4 impaired the endogenous respiration. The endogenous respiration and moisture, temperature, and fertilizer effects decreased in the order L,F1, and F2 layers.