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Showing papers on "Urea published in 1971"


Journal ArticleDOI
TL;DR: Recovery of activity could only be achieved when the required components were mixed prior to removal of urea, suggesting that one or more of these proteins may refold improperly on removal of Urea unless the other components are present.

580 citations


Journal ArticleDOI
TL;DR: A simple method is described for directly determining serum urea nitrogen, wtihout deproteinization, which agreed excellently with those obtained by a reference method that makes use of urease and the Berthelot phenate—hypochlorite reaction for ammonia.
Abstract: A simple method is described for directly determining serum urea nitrogen, wtihout deproteinization. The urea in 20 µl of serum or plasma is reacted with diacetylmonoxime in the presence of thiosemicarbazide and cadmium ion under acid conditions. The absorbance of the resulting rose-purple solution is measured at 540 nm. Results agreed excellently with those obtained by a reference method that makes use of urease and the Berthelot phenate—hypochlorite reaction for ammonia. An automated adaptation utilizing the AutoAnalyzer is also described, which eliminates the need for a dialyzer. A further advantage is that the same reagents are used for both methods.

246 citations


Journal ArticleDOI
TL;DR: Investigation of the possibility that cyanate, which is in equilibrium with urea in solution, might itself prevent the sickling of erythrocytes found that in contrast to the high concentration of urea, potassium cyanate irreversibly inhibits sickling to the same extent.
Abstract: The recent use of urea as a treatment for the crisis phase of sickle-cell anemia has prompted us to investigate the possibility that cyanate, which is in equilibrium with urea in solution, might itself prevent the sickling of erythrocytes. We have found that in contrast to the high concentration of urea (1 M) needed to prevent reversibly the in vitro sickling of 80% of the cells, potassium cyanate (0.01-0.10 M) irreversibly inhibits sickling to the same extent. The prevention of sickling is a function of the amount of [14C]cyanate incorporated into acidprecipitable protein (0.1-1.0 mol of cyanate per mol of hemoglobin). Most of the radioactivity is accounted for by carbamylation of the NH2-terminal valine residues of hemoglobin; there is no detectable carbamylation of the lysine or cysteine residues. The reactive species, HN=C=O (isocyanic acid), may be an analog of O=C=O since both compounds bind to the same valine residues of hemoglobin. Deoxygenated sickled cells also incorporate [14C]-cyanate, but the sickling is not reversed. Oxygenation results in normal morphology in 75% of these cells. Upon subsequent deoxygenation, these cells remain normal. Potassium cyanate (5 mM) was also found to be an effective inhibitor of the gelling of deoxyhemoglobin S.

219 citations


Journal ArticleDOI
05 Feb 1971-Science
TL;DR: The addition of urea and ammonium chloride to the reaction mixture permits phosphorylation in high yield with neutral or basic phosphates at temperatures in the range of 65� to 100�C and it is believed that this procedure plausible model for prebiotic phosphorylated nucleosides.
Abstract: Previous attempts to phosphorylate nucleosides by heating with inorganic phosphate succeeeded only when acid phosphates such as Ca(HPO 4 ) 2 were used. The addition of urea and ammonium chloride to the reaction mixture permits phosphorylation in high yield with neutral or basic phosphates at temperatures in the range of 65° to 100°C. Since the abundant mineral, hydroxylapatite, is a satisfactory substrate for this reaction, we believe that this procedure plausible model for prebiotic phosphorylation.

199 citations


Journal ArticleDOI
TL;DR: In this article, the authors evaluated more than 100 compounds as inhibitors of urease activity in soils and found that dihydric phenols and quinones were the most effective organic compounds tested.
Abstract: Studies to evaluate more than 100 compounds as inhibitors of urease activity in soils showed that dihydric phenols and quinones were the most effective organic compounds tested and that silver and mercury salts were the most effective inorganic compounds. When the most potent inhibitors were compared using 50 μg of inhibitor per g of soil, their effectiveness decreased in the order: catechol > phenylmercuric acetate > hydroquinone >p-benzoquinone and 2,5-dichloro-p-benzoquinone > 2,6-dichloro-p-benzoquinone > silver sulfate > 1,2-naphthoquinone > phenol > mercuric chloride > sodium p-chloromercuribenzoate and 4-chlorophenol > 2,5-dimethyl-p-benzoquinone > N-ethylmaleimide > gold chloride > aceto-hydroxamic acid and copper sulfate. The inhibitory effects of most of these compounds on soil urease activity decreased markedly with time, but the effect of 2,5-dimethyl-p-benzoquinone increased, presumably because this compound is decomposed in soils to a relatively stable product more effective than the parent compound as a soil urease inhibitor. The findings concerning the rates of inactivation of urease inhibitors in soils indicate that, of the various compounds tested, 2,5-dimethyl-p-benzoquinone, 2,5-dichloro-p-benzoquinone, and 2,6-dichloro-p-benzoquinone are likely to prove the most effective for retardation of urea decomposition in soils and reduction of the problems caused by the normally rapid hydrolysis of fertilizer urea by soil urease. N-Serve and other compounds used to inhibit nitrification in soils have very little, if any, effect on soil urease activity.

187 citations


Journal ArticleDOI
Nobuo Ul1
TL;DR: It is concluded that isoelectric focusing is not only useful for the fractionation of protein mixtures and for the determination of isOElectric points of proteins, as currently accepted, but also valuable for conformational studies of some proteins, especially those with known chemical structure.

158 citations


Journal ArticleDOI
TL;DR: Data from the literature on the equilibrium between urea and cyanate which were difficult to combine, have been correlated by computer calculation and accumulation of cyanate in urea solutions was quantitatively studied.

149 citations


Journal ArticleDOI
TL;DR: A kinetic, NADH-coupled, method is described for the measurement of urea in whole blood, serum or plasma which correlates well with the AutoAnalyzer diacetyl monoxime method.

124 citations


Journal ArticleDOI
TL;DR: It is suggested that barley diets for early-weaned lambs can with advantage be supplemented with non-protein N to increase the crude protein in the dry matter up to about 12%.
Abstract: 1. The effects of adding increasing supplements of urea to mainly barley diets for early-weaned lambs were investigated in two experiments. In the first experiment the passage of nutrients along the alimentary tract was studied by taking samples of abomasal, ileal and rectal contents and using a marker technique. In the second experiment, feed consumption and rate of gain were recorded over the growth period up to 40 kg live weight, and nitrogen balances were carried out. In the second experiment a barley-fish meal diet was also included.2. The fermentation of organic matter in the rumen increased with the amount of urea in the diet and levelled off when the diet contained about 12% crude protein.3. Urea supplementation had significant effects in increasing N retention and rate of live-weight gain and in decreasing feed conversion ratio, but supplementation beyond about 12% crude protein in dry matter had no further effect on these measurements. In each instance results with the barley–fish meal diet were better than the results with any of the barley-urea diets.4. From the concentrations of diaminopimelic acid (DAPA) in abomasal fluid it was estimated that microbial protein was produced in the rumen at a rate of 15.6% g/100 g organic matter fermented. This ratio did not appear to alter significantly with urea supplementation, but the comparison depends on the assumption that the concentration of DAPA in the bacterial protein did not itself change with urea supplementation.5. Using results from both experiments, it was calculated that the retained N on the urea-supplemented barley diets was approximately 47% of the amount of protein N absorbed in the small intestine.6. It is suggested that barley diets for early-weaned lambs can with advantage be supplemented with non-protein N to increase the crude protein in the dry matter up to about 12%. When barley diets are given with a protein supplement the addition of non-protein N is unlikely to be beneficial unless the protein supplement is given in such a way that it is not subject to degradation to yield ammonia in the rumen.

124 citations


Journal ArticleDOI
TL;DR: Isoelectric focusing of proteins in urea appears to be useful in the study of various aspects of protein structure and demonstrates heterogeneity in bovine plasma albumin based on primary-sequence differences.
Abstract: 1. An analytical technique of isoelectric focusing in thin layers of polyacrylamide gel has been used to determine the isoelectric point, pI, of several proteins in the presence and in the absence of concentrated urea. 2. The presence of urea did not greatly affect pI except for bovine plasma albumin, where an increase of approx. 1pH unit was found. 3. Evidence is presented that this change in the pI of bovine plasma albumin is due to the normalization of certain ionizable groups on unfolding of the protein in urea. 4. Evidence is also presented that prolonged exposure of bovine plasma albumin to urea results in intramolecular disulphide interchange and that, on removal of urea, the new patterns of disulphide bonding stabilize abnormal conformations with pI values intermediate between those of the native and denatured states. 5. The studies demonstrate heterogeneity in bovine plasma albumin based on primary-sequence differences. 6. Isoelectric focusing of proteins in urea appears to be useful in the study of various aspects of protein structure.

120 citations


Journal ArticleDOI
TL;DR: The rate of urea excretion by goldfish was dependent on the 24-hr experimental ammonia levels but was not affected by the concentration of ambient ammonia during acclimation or the duration of acclimations.

Journal ArticleDOI
TL;DR: Urea has been used as a protein replacement for ruminants for almost a century as discussed by the authors, and it has been known that ruminant animals have the unique ability to convert nonprotein nitrogen (NPN) to protein.

Journal ArticleDOI
TL;DR: The colon is relatively impermeable to urea, urea from the circulation is hydrolysed more readily than that in the lumen, colonic urease activity, although bacterial, has a mucosal or juxtamucosal location, and ammonia generated from ureolysis passes to the circulation rather than theLumen of the colon by nonionic and simple ionic diffusion.


Journal ArticleDOI
TL;DR: In this paper, a simple method of studying the abilities of different compounds to inhibit urease activity in soils is described, which involves determination of the effect of the test compound on the amount of urea hydrolyzed by incubation of soils with urea and toluene at 37°C for 5 hours, urea hydrysis being estimated by colorimetric determination of urerea in the extracts obtained by treatment of the incubated samples with 2 M KC1 containing a urea inhibitor (phenylmercuric acetate).
Abstract: A simple method of studying the abilities of different compounds to inhibit urease activity in soils is described. It involves determination of the effect of the test compound on the amount of urea hydrolyzed by incubation of soils with urea and toluene at 37°C for 5 hr, urea hydrolysis being estimated by colorimetric determination of urea in the extracts obtained by treatment of the incubated samples with 2 M KC1 containing a urease inhibitor (phenylmercuric acetate). The method is rapid and precise, and it is readily adapted for studies of the rate of inactivation of urease inhibitors in soils.

Journal ArticleDOI
TL;DR: The direction of a positive concentration difference for urea across the placenta is important, not only qualitatively in determining the pathway for excretion of urea produced by the fetus, but also quantitatively.

Journal ArticleDOI
TL;DR: In this paper, a change-over experiment to four sheep with cannulas in the abomasum and in the terminal ileum was conducted, and the disappearance of protein, ether extractives, starch, and ash in various segments of the alimentary canal, and of the production of volatile fatty acids when the urea supplements were given.
Abstract: 1. Diets of rolled barley supplemented with urea or fish meal at four different levels were given in a change-over experiment to four sheep with cannulas in the abomasum and in the terminal ileum.2. Estimates were made of the disappearance of protein, ether extractives, starch, and ash in the various segments of the alimentary canal, and of the production of volatile fatty acids when the urea supplements were given.3. The disappearance (Y, g/d) of non-ammonia crude protein from the small intestine increased with increasing protein intake (X, g/d) on the fish-meal diets according to the equation Y = 0.37X+44. There was no increase in the disappearance with the urea supplements.4. In agreement with earlier work, it was shown that faecal nitrogen excretion was influenced to a much greater extent by fermentation in the large intestine than by that in the rumen. There was an apparent synthesis of ether-extractable lipid in the rumen at rates of 21and 18 g/d with the urea and the fish-meal diets respectively.5. The energy of the volatile fatty acids produced when the urea diets were given was estimated to be 59% of the digestible energy consumed.

Journal ArticleDOI
TL;DR: The changes in urinary and renal tissue composition induced by continuous, intravenous infusion of lysine‐vasopressin for up to 4½ hr in water‐loaded, conscious rats were determined.
Abstract: 1. The changes in urinary and renal tissue composition induced by continuous, intravenous infusion of lysine-vasopressin (2·5, 5, 15 and 60 μ-u./min. 100 g body wt.) for up to 4½ hr in water-loaded, conscious rats were determined. 2. Both the magnitude of, and the time required to attain, maximal and stable responses, in respect to both urinary and tissue composition, varied with the dose. 3. The dose-dependent changes in medullary composition were compounded of graded decreases in water content and graded increases in solute (mainly Na and urea) content. 4. The relative contribution of the changes in water, Na and urea contents varied with time and with dose. Significant increases in papillary urea content occurred with all doses. The range of change in urea content was wider than that for any other solute. 5. At low doses, the changes in urinary flow and osmolality were ascribable, almost entirely, to large decreases in free-water clearance, with minor changes in medullary composition; at higher doses, the increases in urinary osmolality were accompanied by steep increases in medullary solute concentrations. 6. A variable, dose-dependent, transient natriuresis occurred during the phase of increasing medullary Na concentration; the peak natriuresis preceded the times of maximal osmolal and Na concentrations in the papilla and urine. 7. The differences in osmolal, urea and Na concentrations between papilla and urine also changed with time. 8. Both the transitional and steady-state changes induced by lysine-vasopressin are discussed in terms of intrarenal mechanisms. It is concluded that the data are most reasonably interpreted on the basis that several hormone-sensitive loci exist in the kidneys, each with individual dose—response and kinetic characteristics.

Journal ArticleDOI
TL;DR: There appears to be a lack of correlation between the levels of ornithine-urea cycle enzyme activity and the pattern of nitrogen excretion in the blood of Opsanus tau.
Abstract: 1. 1. Relatively high activities of all five of the ornithine-urea cycle enzymes were found in liver of the teleost Opsanus tau. 2. 2. The substrate and cofactor requirements of these enzymes appear to be the same as those of most other vertebrates. 3. 3. Concentrations of urea and ammonia in the blood of Opsanus tau are low, and the rate of urea excretion is low compared with the rate of ammonia excretion. 4. 4. Thus, there appears to be a lack of correlation between the levels of ornithine-urea cycle enzyme activity and the pattern of nitrogen excretion.

Journal ArticleDOI
TL;DR: It has been demonstrated by comparative electrophoresis on polyacryalmide gels, that long contact of α-crystallin with urea eventually gives rise to a high degree of carbamylation which may lead to erroneous conclusions about the number of real subunits.


Journal ArticleDOI
TL;DR: The PMR results are most consistent with a weak binding mechanism for urea action, and changes in the water signal are thought to be caused by denaturation of the protein.

Journal ArticleDOI
TL;DR: Results of two greenhouse pot experiments with common bermudagrass and a third with uncropped soil in controlled environment regimes showed that the rate of dissolution of SCU increased greatly with higher temperatures of cropping or incubation, and losses of N were reduced, but not entirely eliminated by S-coating.
Abstract: Greenhouse and laboratory studies were conducted to measure the factors controlling release of N from sulfurcoated urea (SCU). Results of two greenhouse pot experiments with common bermudagrass (Cynodon dactylon) and a third with uncropped soil in controlled environment regimes showed that the rate of dissolution of SCU increased greatly with higher temperatures of cropping or incubation. Dissolution rates of SCU granules were decreased by heavier coating with S, by inclusion of 0.5% coal tar oil microbicide in the coating, and by surface application, as compared to mixing with the soil. Satisfactorily coated urea (SCU) or split applications of uncoated ammonium nitrate (AN) or urea both resulted in more uniform distribution of forage production and N uptake than did a single application of urea or AN at time of seeding. Greater yields of forage were obtained from single applications of some SCU products than from urea or AN. Apparent volatilization losses of surface-applied urea were severe, particularly at higher growth or incubation temepratures. Losses of N were reduced, but not entirely eliminated by S-coating.

Journal Article
TL;DR: A hydrogen exchange model in which the low E*app exchange takes place from folded RNase and the high E-app exchange take place from thermally unfolded RNase accounts for the temperature, pH, urea, and ethanol dependence of RNase hydrogen exchange kinetics.


Journal ArticleDOI
TL;DR: A Chlorella extract capable of cleaving urea to CO2 and NH3 in the presence of ATP has been separated into two enzymes neither of which demonstrates this activity alone, and both decomposes allophanate without added cofactors.

Book ChapterDOI
TL;DR: One of the most important results of a defect of the biosynthesis of urea is an increased level of blood ammonia, so it is essential to consider other conditions that might affect indirectly the urea cycle or in some other way raise the blood ammonia.
Abstract: Publisher Summary Urea is the main end product of nitrogen metabolism. It is formed from the ammonia arising from the metabolism of the amino acids of protein by a sequence of five reactions, four of which comprise the urea cycle proper. The end result is the conversion of ammonia into urea, with the reformation of the individual reactants of the cycle. Compared with other metabolic pathways, the urea cycle is short, possibly the shortest of all. Defects of the enzymes mediating all four reactions of the urea cycle proper have now been established, and there is some evidence of the existence of a fifth enzyme defect, involving carbamyl phosphate synthetase, mediating the initial reaction of the pathway. One of the most important results of a defect of the biosynthesis of urea is an increased level of blood ammonia. Therefore, it is essential to consider other conditions that might affect indirectly the urea cycle or in some other way raise the blood ammonia. Because lysine can act as a competitive inhibitor of the conversion of arginine to ornithine and urea, an increased level of plasma lysine may therefore inhibit the urea cycle.


Journal ArticleDOI
TL;DR: The formation of NH3 and CO2 indicated that pathways of urea catabolism are linked to pathways involved in theCatabolism of carbohydrate in a salivary sediment system.