Showing papers on "Urea published in 1969"

Jack bean urease (EC 3.5.1.5). Demonstration of a carbamoyl-transfer reaction and inhibition by hydroxamic acids

Abstract: A carbamoyl-transfer reaction has been demonstrated in the urease-catalyzed hydrolysis of urea, using a thymol blue buffer to give a sensitive spectrophotometric measure of acidity changes. This demonstration offers further support for the proposition that carbamate is the first product of the urease-catalyzed hydrolysis of urea. The inhibition of urease by acetohydroxamic acid and chloroacetohydroxamic acid has been studied from both directions and found to be completely reversible. Hydroxyurea, itself a substrate, shows a time-dependent inhibition, completely reversible on consumption of hydroxyurea. Electron microscopy suggests that there are six subunits per 483,000 molecular weight species.

EDTA and urea peroxide for root canal preparation

Abstract: Early combinations of EDTA and urea peroxide led to discoloration and crystallization. A new formula, using a stable carbowax base can have clinical value in permitting medication to permeate the root structure more completely and destroy remaining microorganisms.

An Improved Urea Specific Enzyme Electrode

Abstract: The enzyme urease was immobilized in a layer of acrylamide polymer on the surface of a Beckman cationic electrode sensitive to ammonium ion. The substrate urea diffuses to the enzyme electrode and reacts with the immobilized enzyme to produce ammonium ion at the surface of the glass electrode. By placing a thin film of cellophane around the enzyme gel layer to prevent leaching of urease into the surrounding solution, an electrode could be used continuously for over 21 days at 25[ddot]C with no loss of activity.

Assay of urease activity using 14C-urea in stored, geologically preserved, and in irradiated soils

Abstract: Urease activity determined by using C 14 urea in stored, preserved /Permafrost/ and irradiated soils

Urea determination and electrode therefor

Abstract: THE INVENTION CONCERNS A POTENTIOMETRIC METHOD OF DETERMINING THE UREA CONTENT OF FLUIDS BY USE OF A CATION SENSITIVE ELECTRODE HAVING A UREASE LAYER ON ITS SURFACE.

Anomalous Transport of Sucrose and Urea in Toad Skin

Abstract: 1. Increased permeability to sucrose and anomalous transport of this substance in the inward direction are elicited in toad skin when the outside bathing solution is made hyperosmotic by addition of 200 millimoles of urea per liter. Influx and efflux of sucrose are measured on paired halves of skins from the belly of the toad, using 14C-sucrose as a tracer. 2. When the hydrostatic pressure of the inside solution is raised 25 cm H2O over that of the outside solution, the flux asymmetry for sucrose is substantially reduced. 3. Similar experiments with 14C-urea as the ‘driven species’ and inactive urea as the ‘driving species’ gave similar results: Increased permeability and anomalous inward transport. The effect of a hydrostatic pressure difference on the flux ratio was, however, less apparent than in the case of sucrose. 4. At low urea concentrations there seems to be a slow inward active transport of urea between identical solutions. The phenomenon is absent in frog skin. 5. The anomalous transports of sucrose and urea are discussed in the light of a model involving ‘anomalous solvent drag’.

Sulphur metabolism in sheep. IV. The effect of a varied dietary sulphur content on some body fluid sulphate levels and on the utilization of urea-supplemented roughage by sheep

Abstract: A diet composed of oaten hulls, urea, and mineral mixture was shown to be deficient in sulphur with respect to the nutrition of sheep. Sulphate supplements to the diet increased both crude fibre digestion and nitrogen and sulphur retention. They also increased the concentration of inorganic sulphate in the blood and the levels of total sulphur and total sulphate sulphur in the parotid saliva, but decreased blood urea nitrogen levels and the concentration of residual nitrogen and residual sulphur (protein fraction) in the parotid saliva. The effect of these concentration changes is discussed with particular reference to the feeding of sheep on low sulphur, low nitrogen forages.

The transfer of nitrogen from the blood to the rumen in cattle

Abstract: A Brahman x Hereford and a Hereford steer fed on a chaffed tropical pasture hay were infused intravenously and intraruminally with urea at 9–45 g N/day. By comparing the respective increases in rumen ammonia concentration which occurred when urea was infused intravenously and intraruminally, it was possible to estimate the net flow of urea into the rumen resulting from the intravenous administration. In both steers there was a limit to the net amount of urea passing from the blood to the rumen of c. 17–20 g N/day, which was reached at plasma urea concentrations of c. 12 mg N/100 ml. This concentration of plasma urea was achieved in the Brahman x Hereford steer when c. 23 g N/day was infused intravenously but in the Hereford when 32–35 g N/day was infused.

Binding sites of cholinesterases. Alkylation by an aziridinium derivative.

Abstract: 1. Alkylation of acetylcholinesterase and butyrylcholinesterase by 2-chloro-N-(chloroethyl)-N-methyl-2-phenylethylamine was observed. This alkylating agent was more potent than related compounds previously described, and less stable (half-life 8·5min. at 23°). 2. Alkylation had effects on hydrolysis of substrates varying from activation for indophenyl acetate to inhibition for acetylcholine, and intermediate effects with five other substrates. The effects were on Vmax. and not Km. 3. Alkylation caused a variety of changes in sensitivity to inhibition by five carbamates, five organophosphates and four other inhibitors, varying from total protection against tetraethylammonium to mildly enhanced sensitivity to urea. 4. The findings suggested the existence of three binding sites, one of which was anionic and another hydrophobic, in addition to the esteratic site.

Free Water Excretion and Washout of Renal Medullary Urea by Prostaglandin E1

Abstract: Prostaglandin E1 (PGE1) was infused directly into the left renal artery of anesthetized dogs. In the infused kidney, there occurred increases in sodium and water excretion with increased RPF and decreased EPAH. Distinctly hypotonic urine was excreted even without solute diuresis in the infused kidney, when control urine and urine in contralateral kidney was hypertonic. Rapid washout of renal medullary urea was also observed in the infused kidney and transitory increase in urea excretion made urea to creatinine clearance ratio more than unity. The effects may have resulted from either hemodynamic effect alone or from both hemodynamic and anti-ADH effect of PGE1. The present study may seem to support the presence of a direct anti-ADH action of PGE1 in vivo.

Effect of urine flow rate on urea reabsorption in man: urea as a "tubular marker".

Abstract: GOLDSTEIN, MARVIN H., PAUL K. LENZ, AND MARVIN F. LEVITT. Efect of urine jaw rate on urea reabsorption in man: urea as a “tubular marker. ” J. Appl. Physiol. 26(5): 594-599. 1969.Studies were performed in man to determine the magnitude of distal tubular urea reabsorption at different urine flow rates. Of filtered urea, 60y0 was reabsorbed during hydropenia and 35y0 during hydration. Diuretics inhibiting proximal or distal tubular sodium and water reabsorption were administered after achieving high urine flows by hydration or by modest osmotic loads with added ADH. The percent of filtered urea excreted increased with proximal but not with distal agents, suggesting that urea was not reabsorbed in the distal segments. The findings that urea reabsorption was confined to the proximal tubule with high urine flows and that only 2574 was reabsorbed distally during hydropenia indicates the relative impermeability of the distal tubule to urea. Since sodium and water reabsorption was associated with parallel changes in urea reabsorption in the proximal but not in the distal tubule, it appears that analysis of changes in the percent of filtered urea excreted may be useful in localizing alterations in sodium and water reabsorption to specific tubular segments within the human nephron.

Studies with 15N-labeled ammonia and urea in the malnourished child

Abstract: Investigations using ammonium citrate-(15)N and urea-(15)N showed that children in the acute stage of kwashiorkor and marasmus receiving a diet of adequate protein content retained a considerable percentage of the label from both compounds. Excretion of both total (15)N and urea-(15)N was subnormal and elimination was virtually completed 36 hr after administration of the isotope. During recovery from kwashiorkor total (15)N excretion had approached normal a month after commencement of rehabilitation. Urea-(15)N excretion was still slightly subnormal after 3 months. In marasmus urea-(15)N formed a normal proportion of total (15)N excretion after 1 month, although total (15)N excretion then was still low. Ammonia nitrogen was retained to a greater extent than urea nitrogen in all cases. As it is known that a considerable amount of urea is degraded to ammonia in the gastrointestinal tract, it seems probable that urea nitrogen became available for use after this degradation. Examination of blood from one marasmic child after feeding ammonia-(15)N and from another after intravenous injection of urea-(15)N showed incorporation of the label into blood cells and plasma proteins. This did not occur in well nourished controls. It is concluded that ammonia and urea as sources of nonessential nitrogen may play an important part in protein metabolism in the malnourished child.

The Renal Excretion of Nitrogenous Compounds by the Duck (Anas Platyrhynchos) Maintained on Freshwater and on Hypertonic Saline

Abstract: 1. The excretory rates of total nitrogen, uric acid, urea and ammonia by intact birds maintained on fresh water did not differ significantly from the corresponding rates of excretion by birds maintained on saline equivalent to 60% sea water (284 mM-NaCl, 6.0 mM-KCl). 2. The uric acid excreted by these birds contributed 53.8%, the ammonia 29.2% and the urea 1.5% of the total nitrogen excreted. The three compounds together accounted for 84.5% of the nitrogen excreted. 3. The glomerular filtration rates (inulin clearance) and the renal plasma flow rates (PAH clearance) did not differ between the freshwater-maintained and the salinemaintained birds. 4. The clearance of uric acid in all groups of birds was equal to the PAH clearance and may be interpreted as a reliable measure of the renal plasma flow rate. 5. The urea:inulin clearance ratios for the individual urine samples from all birds suggested that renal tubular synthesis and secretion of urea may occur. 6. In a second set of experiments uric acid and urea concentrations in the plasma of fed ducks were followed during adaptation to hypertonic saline and during a similar period of dehydration. 7. A sharp in the increase plasma uric acid concentration was generally observed in all groups of birds after feeding and the concentration then gradually declined to the prefeeding level. 8. The plasma urea concentrations of birds given saline equivalent to 60% sea water equilibrated, after the first 24 hr., at about twice the concentration found in the freshwater-maintained birds. 9. In birds maintained on saline equivalent to 100% sea water (470 mM-NaCl; 10 mM-KCl), the plasma urea concentration steadily rose during the first 50 hours and then equilibrated at a level approximately 10 times that observed in freshwatermaintained birds. 10. Withholding all drinking water from birds which had been previously given fresh water resulted in a rise in the plasma urea concentration during the first 50 hr. similar to that observed in the birds maintained on saline equivalent to 100% sea water. But the plasma urea concentration of these birds, in contrast to that of salinemaintained birds, continued to rise throughout the remainder of the experimental period. This work was supported by a research grant to W. N. H. from the National Science Foundation (grant no. GB 3896). N.D.E.A. (title IV) pre-doctoral fellow.

Metabolism of Urea by Chlorella vulgaris

Abstract: Urea metabolism was studied with nitrogen-starved cells of Chlorella vulgaris Beijerinck var. viridis (Chodat), a green alga which apparently lacks urease. Incorporation of radioactivity from urea-14C into the alcohol-soluble fraction was virtually eliminated in cell suspensions flushed with 10% CO2 in air. This same result was obtained when expected acceptors of urea carbon were replenished by adding ornithine and glucose with the urea. Several carbamyl compounds, which might be early products of urea metabolism and a source of the 14CO2, were not appreciably labeled. If cells were treated with cyanide at a concentration which inhibited ammonia uptake completely and urea uptake only slightly, more than half of the urea nitrogen taken up was found in the medium as ammonia. Cells under nitrogen gas in the dark were unable to take up urea or ammonia, but the normal rate of uptake was resumed in light. Since 3-(3,4-dichlorophenyl)-1,1-dimethylurea did not selectively inhibit this uptake, an active respiration supported by light-dependent oxygen evolution in these cells was ruled out. A tentative scheme for urea metabolism is proposed to consist of an initial energy-dependent splitting of urea into carbon dioxide and ammonia. This reaction in Chlorella is thought to differ from a typical urease-catalyzed reaction by the apparent requirement of a high energy compound, possibly adenosine triphosphate.

The effect of protein content of the diet on the rate of urea formation in sheep liver

Abstract: 1. In the livers of six sheep given a high-protein diet, the concentrations of certain urea-cycle enzymes [ornithine transcarbamoylase, arginine synthetase (combined activity of argininosuccinate synthetase and argininosuccinase) and arginase] were significantly greater than when the sheep were given a low-protein diet. Alkaline phosphatase activity/mg. of liver protein was not significantly affected by diet. 2. Three sheep previously given the high-protein diet showed no significant rise in the concentration of ammonia in the blood after the administration of urea (0·5g./kg. body wt.). The concentration of ammonia in the blood of the three sheep given the low-protein diet rose exponentially with time after dosing with urea and all sheep died. 3. It is suggested that tolerance to ammonia toxicity in the sheep is at least partly a function of the activity of the urea-cycle enzymes in the liver.

Urea in Reactive Dyeing

Abstract: The effect of urea on formation and cleavage of a covalent bond between a reactive dye and cellulose has been investigated. The evidence presented is consistent with the view that urea increases th...