Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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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)

Lenses produce both ammonia and urea, and a previous report suggested that bovine lenses contain a complete urea cycle capable of synthesizing urea from bicarbonate and ammonia. To determine whether lenses produce urea by a complete urea cycle or by arginase alone, intact lenses were cultured with [guanido-14C]-arginine or [14C]-bicarbonate. The [14C]-urea was volatilized to [14C]-CO2 by urease and collected in KOH. The cultured rat, bovine and human lenses produced [14C]-urea from [14C]-arginine; therefore lens arginase activity was also examined in homogenates of rat and human lenses. Rat lens homogenates had constant arginase activity for at least 2 hr at 37 degrees C, and activity increased linearly with the concentration of lens homogenate. Rat lens arginase had an apparent Vmax of approximately 13 nmol/hr/mg lens wet weight in lens homogenates and produced 4-6 nmol urea/hr/mg at 25 mM arginine. Human lens homogenates produced 1-5 nmol/hr/mg. In contrast, neither bovine nor rat lenses cultured with [14C]-bicarbonate produced detectable [14C]-urea, although label was incorporated into unidentified nonvolatile products. These products were shown by ion exchange chromatography and enzymatic assay to contain no detectable arginine or urea. It was concluded that although arginase activity is present, neither rat nor bovine lenses contain significant urea cycle activity. However, it is possible that arginase serves as a source of lens ornithine.
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PMID:Urea formation in rat, bovine, and human lens. 666 5

To examine the rate-of-living theory, age-related changes in amino acid pool sizes were investigated in the adult silkmoth, Bombyx mori, reared at low and high temperature. At either temperature concentrations of free amino acids contained in silkmoths revealed a great sexual difference. Those in females were generally much higher than in males and the former changed much more dynamically than the latter. Major amino acids or ninhydrin-positive compounds inclusive of some essential amino acids such as Leu, Ile, Val, Thr, Arg, Phe, Met, Ala, Tyr, Gln, Aspn , Lan , Cysta , GABA and PEA accumulated in 4 degrees C-moths. However, the levels of these amino changed irregularly with advanced age. Inhibition of protein synthesis may occur generally at low temperature, while protein degradation may be promoted at high temperature. High concentrations of MSO and Tau in the moths reared at high temperature than in the normal moths suggested also catabolism of amino acids proceeding together with protein degradation at high temperature. Amino acid metabolism seems to be complicated under various temperature conditions. When reared at the optimal temperature of 25 degrees C, urea is not present in the body of the silkmoth except for a slight amount in the secreted meconium. In silkmoths reared at the higher temperature of 35 degrees C, however, an extraordinary accumulation of urea occurs accompanied by a reduction in lifespan by one half. Undoubtedly, urea is produced in this terrestrial insect, although the accumulation mechanism is not clear: in silkmoths reared at various temperatures, arginase is found, but urease is not detected. Arginase activity was found to be higher in male moths than in female moths regardless of the rearing temperature. High temperature rearing also did not induce activity and female activity never exceeded that in males at either 25 degrees C or 35 degrees C rearing. Protein degradation accelerated by rearing at high temperatures may result in increased amounts of free arginine, which could cause the active production of urea. This possibility would be a counter-argument to the rate of living theory relating to longevity and temperature. However, at least the above facts signify that an extrinsic factor influences the longevity of an animal by altering its intrinsic aging process.
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PMID:Age-related changes in amino acid pool sizes in the adult silkmoth, Bombyx mori, reared at low and high temperature; a biochemical examination of the rate-of-living theory and urea accumulation when reared at high temperature. 672 18

A highly sensitive radiochemical assay used to measure the synthesis and regulation of the product of the argH gene, argininosuccinase, in an Escherichia coli system in vitro is described. With L-[guanidino-14C]argininosuccinic acid as a substrate, and in the presence of excess arginase and urease, 14CO2 is collected in a simply designed micro-vessel. With this method less than 1 nmol of product can be measured in the presence of various concentrations of L-arginine.
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PMID:The determination by radiochemical assay of argininosuccinase produced in an Escherichia coli system in vitro. 676 7

L-Canavanine competes with L-arginine for incorporation into vitellogenin secreted in vitro by the fat body of the female locust Locusta migratoria migratorioides. Incorporation of L-[guanidinooxy-14C]canavanine into vitellogenin has been established unequivocally by combined arginase and urease hydrolyses of the acid hydrolysate of antibody-precipitated canavanyl vitellogenin. Continued exposure of the fat body to canavanine decreases in vitro protein secretion but the proportion of canavanyl vitellogenin to native vitellogenin increases. Canavanine-mediated inhibition of fat body protein secretion is dependent on both the canavanine concentration and the arginine retention by the fat body. Canavanine replaces about 10% of the arginyl residues of canavanyl vitellogenin. The electrophoretic mobility of canavanyl vitellogenin is greater than that of native vitellogenin but the ability of this aberrant protein to react with vitellogenin antibody is unimpaired.
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PMID:In vitro incorporation of L-canavanine into vitellogenin of the fat body of the migratory locust Locusta migratoria migratorioides. 694 85

The nitrogen excretory metabolism of the myxomycete Physarum polycephalum was studied. When cultured in partially defined broth medium or on agar, the principal excretory product was ammonia nitrogen. A small, variable quantity of urea was excreted in liquid culture. No uric acid or other purines were detected in the cultures. When microplasmodia were incubated with sodium [14C]bicarbonate, radioisotope was incorporated into citrulline, arginine, and urea. Incubation with L-[carbamoyl-14C]citrulline yielded labelled arginine, urea, and CO2. Substantial urease activity was found in extracts of the microplasmodia. These results, in conjunction with the lack of an absolute nutritional requirement for arginine, provide evidence that Physarum has a functional arginine biosynthetic pathway, an arginase, and a urease.
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PMID:Arginine synthesis and nitrogen excretion in the myxomycete Physarum polycephalum. 737 43

Lectins from the lichen Xanthoria parietina develop arginase activity. One of these lectins behaves as a secreted arginase whereas another is an endocellular enzyme. Both enzymes are glycosylated proteins differing in the occurrence of galactose instead of N-acetyl-D-glucosamine in secreted arginase. The affinity for the algal ligand (glycosylated cell wall urease) of secreted arginase is higher than that shown for the endocellular enzyme. When the lectin ligand is absent from the algal cell wall, both endocellular and secreted arginases seem to be able to enter algal cells. This uptake promotes the increase in the amount of algal putrescine, preferently as free polyamine, and the chloroplast is rapidly damaged. Induction of cell wall urease retains lectins outside the cells, on the cell wall, and chloroplast remains healthy.
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PMID:Correlationships between enzymatic activity of lectins, putrescine content and chloroplast damage in Xanthoria parietina phycobionts. 774 19

Cerebral neurogenic vasodilation is mediated predominantly by nitric oxide (NO). Thus, NO was suggested to be a vasodilator transmitter. In the present study, the possibility that cerebral perivascular nerves can convert citrulline to arginine was examined to ascertain that NO is derived directly from these perivascular nerves. To investigate the uptake of citrulline and its conversion to arginine, both fresh and cold storage-denervated porcine cerebral arteries with or without endothelial cells were incubated at 37 degrees C for 2 hr in Krebs-Ringer bicarbonate buffer containing 0.5 mM purified [14C]ureido-citrulline. The formation of [14C]arginine was measured as 14CO2 by a coupled enzymatic assay involving arginase and urease. The abolishment of nitric oxidergic nerves was verified by NADPH-diaphorase (constitutive NO synthases) histochemical staining method. The results indicated that there was an active conversion of [14C]arginine from [14C]citrulline in nerve-intact arteries denuded of endothelial cells. The conversion was significantly decreased in denervated arteries, accompanied by a significantly reduced citrulline uptake into these denervated arteries. L-Glutamine, but not L-glutamate, gamma-aminobutyric acid, or nitro-L-arginine significantly inhibited the uptake of [14C]citrulline into cerebral perivascular nerves. These data suggest that porcine cerebral vasodilator nerves are nitric oxidergic in nature and citrulline, co-produced with NO by NO synthases from arginine, can be recycled to form arginine in these nerves. The existence of a functional arginine-citrulline cycle may contribute to a constant supply of L-arginine and suggests a neuronal source of NO for inducing cerebral vasodilation.
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PMID:Arginine synthesis from citrulline in perivascular nerves of cerebral artery. 775 95

In Arabidopsis thaliana, urease transcript levels increased sharply between 2 and 4 d after germination (DAG) and were maintained at maximal levels until at least 8 DAG. Seed urease specific activity declined upon germination but began to increase in seedlings 2 DAG, reaching approximately 75% of seed activity by 8 DAG. Urea levels showed a small transient increase 1 DAG and then approximately paralleled urease activity, reaching maximal levels at approximately 9 DAG. Urease inhibition with phenylphosphorodiamidate resulted in a 2- to 4-fold increase in urea levels throughout seedling development. Arginine pools (0-8 DAG) changed approximately in parallel with the urea pool. Consistent with arginine being a major source of urea, arginase activity increased 10-fold in the interval 0 to 6 DAG. Allopurinol, a xanthine dehydrogenase inhibitor, had no effect on urea levels up to 3 DAG but reduced the urea pool by 30 to 40% during the interval 5 to 8 DAG, suggesting that purine degradation contributed to the urea pool well after germination, if at all. in aged Arabidopsis seeds, there was correlation between phenylphosphorodiamidate inactivation of urease and germination inhibition, the latter overcome by NH4NO3 or amino acids. Since urease activity, urea precursor, and urea increase in young seedlings, and since urease inactivation results in a nitrogen-reversible inhibition of germination, we propose that urease recycles urea-nitrogen in the seedling.
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PMID:Essential role of urease in germination of nitrogen-limited Arabidopsis thaliana seeds. 777 May 20

Urea production by cortical (CCD) and medullary (OMCD) collecting ducts of the rat kidney was measured in vitro by incubating single microdissected pieces of tubule in the presence of L-[guanido-14C]arginine (0.2 mM). The [14C]urea released from the cells was hydrolysed in presence of urease added to the incubation medium and the 14CO2 formed was trapped in KOH and counted. The effect of various amino acids (AA) on urea production was investigated by adding unlabelled AA (either in combination or singly) at concentrations close to those present in blood plasma. A mixture of 17 AA decreased urea production from [14C]arginine by 46% in CCD and by 58% in OMCD. When lysine and proline were omitted from the mixture, the inhibition was less marked (19% in CCD and 43% in OMCD, respectively). When AA were tested singly, lysine induced the larger inhibition (40% in CCD and 45% in OMCD), than ornithine and glutamine (about 15% each, in CCD and OMCD), whereas proline inhibition (7% in CCD, 10% in OMCD) was not statistically significant. Branched-chain amino acids (BCAA) in combination (leucine, isoleucine and valine) also markedly reduced urea production by CCD and OMCD. Their effect was dose dependent. Solubilization of CCD and OMCD cell membranes with Triton X-100 resulted in a twofold increase in urea production by control samples; the relative inhibition (per cent) induced by BCAA was enhanced, whereas that induced by lysine was decreased. The data suggest that, in living tubules, the inhibition obtained with lysine resulted, for a large part, from competition between lysine and arginine for cell uptake via a common membrane carrier, whereas the inhibition induced by BCAA corresponded to an effect on arginase activity itself.
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PMID:Urea production by kidney collecting ducts in vitro: effect of amino acid addition. 805 17

In the rat kidney, arginine (Arg) synthesis is restricted to the proximal tubule with a decreasing intensity from its convoluted (PCT) to its straight part (PST). The present study was designed to investigate the pattern of Arg synthesis along the nephron in other mammals, the mouse and rabbit. Microdissected representative nephron segments were incubated with 0.1 mM L-[ureido-14C]citrulline in a sealed chamber. Addition of arginase and urease to the incubation medium led to the hydrolysis of Arg into ornithine, NH3, and 14CO2. The latter was trapped in KOH and counted (results are in fmol Arg.min-1.mm tubular length-1). As in the rat, the main site of Arg synthesis in both species was found to be the PCT (mouse, 191; and rabbit, 57). A lower production was observed in rabbit and mouse PST and in rabbit distal segments. Along the PCT (from 1st to 4th mm after the glomerulus), a steep decrease is observed in mouse (595 and 37, respectively) but not in rabbit (57 and 23). The fate of the newly synthesized Arg probably depends on its site of production. Intracellular arginase activity is known to be present in the cortical (C) and medullary (OS) PST, in both mouse and rabbit. In rabbit only, arginase activity is also found in the PCT. We observed that a large part of Arg was further hydrolyzed into urea and ornithine in CPST and OSPST of mouse (66 and 80%, respectively) and rabbit (40 and 70%) but not in rabbit PCT (8%). Thus Arg produced by PCT in both species is probably released in the cortical blood, whereas Arg produced in PST may serve locally to produce urea and ornithine, and the latter could be used for polyamine synthesis.
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PMID:Arginine synthesis in mouse and rabbit nephron: localization and functional significance. 832 90


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