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Query: EC:6.3.4.6 (urease)
 7,490 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The growth and utilization of nitrogen by intensive Chlorella vulgaris in wastes from production of urea, containing 1300 mg NH4+-N and 4000 mg urea-N/1, was investigated. In these conditions only Chlorella vulgaris AA strain, adapted to high concentrations of ammonia nitrogen, was able to grow. The elimination of nitrogen by continuous cultures was 750 mg urea-N/1 with 5-day flow rate. A considerable part of the urea was hydrolized by urease bacteria and removed in the form of NH3. The effect of intermittent light on the growth of algae was also studied. The better growth than in continuous light, was obtained with alternate one hour periods of light and darkness. Good results were also obtained with the use of 12 hour light and 12 hour darkness.
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PMID:Studies on the purification of wastes from the nitrogen fertilizer industry by intensive algal cultures. IV. growth of Chlorella vulgaris in wastes with high nitrogen content in continuous and intermittent light. 6 57

The regulation of the synthesis of the enzyme urease (urea amido hydrolase E.C. 3.5.1.5.) in Neurospora crassa was investigated. The biosynthesis of urease is repressed by ammonium ions. Under ammonium excess conditions the specific activity of urease decreases from 0.980 to 0.180 mumoles NH3/min/mg protein. By addition of cycloheximide it was shown that ammonia influences the synthesis of this enzyme. Enzyme induction by the substrate could be excluded. Even under the conditions of highest repression a specific activity of urease of 0.180 mumoles NH3/min/mg protein was measured. Possible causes of this constitutive enzyme level are discussed.
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PMID:[Repression of urease biosynthesis in Neurospora crassa by ammonium ions]. 12 30

Urease activity, expressed as mg N-NH3/g dry weight per 30 min at 25 degrees C, was determined in the various parts of the sheep, chicken and pig digestive apparatus. The results were as follows. Sheep: contents--rumen 1.25"/-0.09, reticulum 0.78+/-0.02, omasum 0.44+/-0.02, abomasum 0.002+/-0.001, duodenum 0.003+/-0.001, jejunum 0.18+/-0.03, ileum 0.42+/-0.03, caecum 1.34+/-0.11, colon 0.76+/-0.08, walls-rumen 0.88+/-0.16, reticulum 0.38+/-0.04, omasum 0.11+/-0.02, abomasum 0.01+/-0.002, ileum 0.092+/-0.01, caecum 0.14+/-0.03, colon 0.16+/-0.02. Chicken: contents--jejunum 0.028+/-0.009, ileum 0.043+/-0.013, caecum 0.17+/-0.03, colon and cloaca 0.04+/-0.013. Pigs: contents--jejunum 0.02+/-0.01, ileum 0.14+/-0.08, caecum 0.62+-0.12, colon 0.43+/-0.06. No urease activity was found in the walls of the digestive apparatus or the contents of the duodenum in chickens, or in the walls of the stomach and intestine and the contents of the duodenum in pigs. The results show that urease activity in the digestive apparatus of pigs and poultry is lower than in sheep. Inadequate urease activity in the digestive apparatus explains why chickens and pigs are significantly less capable than ruminants of utilizing urea nitrogen as a substitute for some of the protein in the diet.
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PMID:Urease activity in the contents and tissues of the sheep, pig and chicken gastrointestinal apparatus. 16 May 76

I propose a single, quick method for measuring ammonia in urine and urea in plasma and urine. An ammonia-selective electrodie is used, set up on a microcell, which allows use of small sample volumes. Ammonia is measured directly after partial conversion of ammonium ions to NH3. Urea is measured after its hydrolysis by urease. With urine, the two procedures can be carried out successively in the same cell and on the same sample without changing the procedural conditions. Linear electrode response and accuracy have been checked for concentrations in the expected (normal) range.
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PMID:Determination of ammonia and urea in urine and of urea in blood by use of an ammonia-selective electrode. 49 98

Mucosal cells isolated from the small intestine of chicks and rats were incubated with concentrations of ammonia normally found in the intestinal tract of mammals and birds. NH4Cl added to the incubation medium increased glucose metabolism in cells from both species. Ammonia stimulated incorporation of precursors into RNA and decarboxylation of orotic acid by cells isolated from chickens, but an increase in incorporation of precursors into DNA was not observed in cells from either species. Cultured embryonic chicken duodena showed increased incorporation of orotate into RNA with NH4Cl added to the medium. Rats immunized against jack bean urease showed lower urease activity per gram of dry intestinal content, lower intestinal weight, lower mucosal cell, and total gut protein and less protein per unit weight of DNA in the mucosal cell fraction. The results are compatible with the conclusion that ammonia PRODUCED IN THE INTESTINE BY BACTERIAL UREASES CAUSES SIGNIFICANT CHANGES IN THE CONTENT OF RNA and protein in intestine cells.
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PMID:Synthesis of macromolecules by intestinal cells incubated with ammonia. 91 Sep 48

The break-down of benzamide, acetamide, malonamide and allantoin in M. smegmatis was investigated. It has been stated that the uptake of liberated NH3 into the cells, favoured by the presence of an organic acid, occasionally results in a negative NH3 determination. This difficulty can be overcome by an increase of the substrate concentration from 0.8 up to 4 mM. All antoinase activity in mycobacteria can be demonstrated only by an NH3 determination, when all the enzymes necessary for the complete break-down of allantoin are present. Bacteria containing allantoinase but not urease will be negative in this test. Using high amide concentrations (4 mM) some doubtful results concerning the degradation of acetamide, benzamide, nicotinamide and pyrazinamide can be eliminated as could be demonstrated for different strains of mycobacteria.
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PMID:Biochemical background of some enzymatic tests used for the differentiation of mycobacteria. 96 Feb 26

Urease obtained from seeds of Citrullus vulgaris fruits has been studied under three points of view: a) the effect of the urea analogs acetamide and hydroxi-urea on the enzyme kinetic b) the action of the sulfhydryl reagents and the reactivation agents on the enzyme c) the effect of X-rays and the protective action of the cysteamine. The Berthelot reaction for the determination of the liberated NH3 was used enzyme activity. Acetamide has no effect on urease kinetic. Hidroxy-urea which produces a typical green color when it is mixed with the Berthelot reagents at high concentrations, when properly diluted acts a aompetitive inhibitor of urease. Spectrophotometric experiments suggest that the studied urease decomposes hydroxi-urea with liberation of hydroxilamine. The sulphydril reagent, p-hydroxi-mercuribenzoate inhibits the enzime. Cysteine and dithiotreitol reactivate the enzyme activity in no more then 50% even when excess of the substances is used. Probably only in the first step of the urea hydrolysis, the enzyme behaves as a typical SH-enzyme. Urease is very sensitive to X-rays. Cysteamine acts as a protective agent of the enzyme. Dithiotreitol reinforces this protective action. This effect is clearly observed when the Fisbein catalytic method for urease is employed.
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PMID:[Studies on urease from the seeds of Citrullus vulgaris: action of chemical agents and ionizing radiations]. 103 92

Nitrogen-free analogues of essential amino acids, when administered with those essential amino acids for which analogues are ineffective or unavailable, exert three actions that may be beneficial in protein-deficient or protein-intolerant subjects. First, they bring about an increase in the concentrations of essential amino acids in the blood at the expense of the concentrations of certain non-essential amino acids, notably alanine and glutamine. This effect is most readily demonstrated in children with congenital defects of the urea cycle enzymes, but can also be seen during daily therapy of adults with portal-systemic encephalopathy. Second, these compounds promote nitrogen balance through their suppressive effect on urea synthesis (an effect not attributable to re-utilization of ammonia derived from urease action in the gut). This action is demonstrable in obese subjects who are already conserving nitrogen maximally at the end of a prolonged fast and can also be shown in the first week of fasting when the branched-chain keto acids alone are administered. In both situations, improved nitrogen conservation persists long after the analogues are metabolized, suggesting enzyme adaptations. In chronic uremics, nitrogen balance can be maintained in some (but not all) patients on very low nitrogen intakes. Third, these mixtures may delay or reverse the progressive decline in glomerular filtration rate characteristic of chronic renal failure in some cases: thus, for example, 5 of 6 patients taken off chronic dialysis have maintained lower serum urea concentrations without evidence of protein malnutrition for periods of 2-24 months.
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PMID:Evidence for an anabolic action of essential amino acid analogues in uremia and starvation. 107 39

In the unicellular green alga Chlamydomonas reinhardi (strain y-1), synthesis of the enzymes required for urea hydrolysis is under substrate induction control by urea and under end product repression control by ammonia. Hydrolysis of urea if effected by the sequential action of the discrete enzymes urea carboxylase and allophanate lyase, collectively called urea amidolyase. The carboxylase converts urea to allophanate in a reaction requiring biotin, adenosine 5'-triphosphate, and Mg2+. The lyase hydrolzyes allophanate to ammonium ions and bicarbonate. Neither activity is present in more than trace amounts when cultures are grown with ammonia or urea plus ammonia, or when they are starved for nitrogen for 8 h. Urea in the absence of ammonia induces both activities 10 to 100 times the basal levels. Addition of ammonia to an induced culture causes complete cessation of carboxylase accumulation and an 80% depression of lyase accumulation. Ammonia does not reduce urea uptake by repressed cells, so it does not prevent induction by the mechanism of inducer exclusion. The unicellular green alga Chlorella pyrenoidosa (strain 3 Emerson) also has discrete carboxylase and lyase enzymes, but only the carboxylase exhibits metabolic control.
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PMID:Metabolic control of urea catabolism in Chlamydomonas reinhardi and Chlorella pyrenoidosa. 111 94

Gyrocotyle fimbriata isolated from the spiral valve of Hydrolagus colliei were washed, then held in a filtered seawater-penicillin-Tris buffer medium. Ammonia and urea release to the medium declined together and ammonia production was minimal when the urea concentration was below detectable limits. Alanine and smaller amounts of glycine were released to the medium at a more constant rate. After 12 hr the alanine-glycine excretion was more than 20 times the ammonia excretion. L-arginine, L-serine, L-histidine, and urea were most effective in stimulating ammonia production by whole worms; other L-amino acids were essentially ineffective. L-glutamate dehydrogenase, L-amino acid oxidase, uricase, and ornithine transcarbamylase were below detectable levels. L-serine dehydrase, L-arginase, L-histidase, and urease were detected in tissue homogenates and probably account for most of the endogenous ammonia production. L-arginase has a molecular weight of 28,000 by Sehpadex gel filtration. The high levels of glutamate-pyruvate transaminase and lower levels of glutamate-oxalacetate transaminase correlate with the high level of alanine excretion. It is concluded that (1) ammonia production is not strongly linked to the overall energy metabolism of Gyrocotyle and is probably a result of a series of unrelated enzymatic reactions such as the action of urease of urea from the tissue of the rat fish, and (2) alanine and glycine are the major nitrogen excretory products and their production is linked to the energy metabolism of Gyrocotyle.
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PMID:Ammonia formation and amino acid excretion by Gyrocotyle fimbriata (Cestoidea). 111 78


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