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PubMed2000

Helicobacter pylori urease suppresses bactericidal activity of peroxynitrite via carbon dioxide production.

Helicobacter pylori can produce a persistent infection in the human stomach, where chronic and active inflammation, including the infiltration of phagocytes such as neutrophils and monocytes, is induced. H. pylori may have a defense system against the antimicrobial actions of phagocytes. We studied the defense mechanism of H. pylori against host-derived peroxynitrite (ONOO(-)), a bactericidal metabolite of nitric oxide, focusing on the role of H. pylori urease, which produces CO(2) and NH(3) from urea and is known to be an essential factor for colonization. The viability of H. pylori decreased in a time-dependent manner with continuous exposure to 1 microM ONOO(-), i.e., 0.2% of the initial bacteria remained after a 5-min treatment without urea. The bactericidal action of ONOO(-) against H. pylori was significantly attenuated by the addition of 10 mM urea, the substrate for urease, whereas ONOO(-)-induced killing of a urease-deficient mutant of H. pylori or Campylobacter jejuni, another microaerophilic bacterium lacking urease, was not affected by the addition of urea. Such a protective effect of urea was potentiated by supplementation with exogenous urease, and it was almost completely nullified by 10 microM flurofamide, a specific inhibitor of urease. The bactericidal action of ONOO(-) was also suppressed by the addition of 20 mM NaHCO(3) but not by the addition of 20 mM NH(3). In addition, the nitration of L-tyrosine of H. pylori after treatment with ONOO(-) was significantly reduced by the addition of urea or NaHCO(3), as assessed by high-performance liquid chromatography with electrochemical detection. These results suggest that H. pylori-associated urease functions to produce a potent ONOO(-) scavenger, CO(2)/HCO(3)(-), that defends the bacteria from ONOO(-) cytotoxicity. The protective effect of urease may thus facilitate sustained bacterial colonization in the infected gastric mucosa.

Ammonia↗
PubMed2002

NikR mediates nickel-responsive transcriptional induction of urease expression in Helicobacter pylori.

The important human pathogen Helicobacter pylori requires the abundant expression and activity of its urease enzyme for colonization of the gastric mucosa. The transcription, expression, and activity of H. pylori urease were previously demonstrated to be induced by nickel supplementation of growth media. Here it is demonstrated that the HP1338 protein, an ortholog of the Escherichia coli nickel regulatory protein NikR, mediates nickel-responsive induction of urease expression in H. pylori. Mutation of the HP1338 gene (nikR) of H. pylori strain 26695 resulted in significant growth inhibition of the nikR mutant in the presence of supplementation with NiCl(2) at > or =100 microM, whereas the wild-type strain tolerated more than 10-fold-higher levels of NiCl(2). Mutation of nikR did not affect urease subunit expression or urease enzyme activity in unsupplemented growth media. However, the nickel-induced increase in urease subunit expression and urease enzyme activity observed in wild-type H. pylori was absent in the H. pylori nikR mutant. A similar lack of nickel responsiveness was observed upon removal of a 19-bp palindromic sequence in the ureA promoter, as demonstrated by using a genomic ureA::lacZ reporter gene fusion. In conclusion, the H. pylori NikR protein and a 19-bp operator sequence in the ureA promoter are both essential for nickel-responsive induction of urease expression in H. pylori.

Base Sequence↗
PubMed1990

Genetic analysis of Escherichia coli urease genes: evidence for two distinct loci.

Studies with two uropathogenic urease-producing Escherichia coli strains, 1021 and 1440, indicated that the urease genes of each are distinct. Recombinant plasmids encoding urease activity from E. coli 1021 and 1440 differed in their restriction endonuclease cleavage sites and showed minimal DNA hybridization under stringent conditions. The polypeptides encoded by the DNA fragments containing the 1021 and 1440 urease loci differed in electrophoretic mobility under reducing conditions. Regulation of urease gene expression differed in the two ureolytic E. coli. The E. coli 1021 locus is probably chromosomally encoded and has DNA homology to Klebsiella, Citrobacter, Enterobacter, and Serratia species and to about one-half of the urease-producing E. coli tested. The E. coli 1440 locus is plasmid encoded; plasmids with DNA homology to the 1440 locus probe were found in urease-producing Salmonella spp., Providencia stuartii, and two E. coli isolates. In addition, the 1440 urease probe was homologous to Proteus mirabilis DNA.

Blotting, Southern↗
PubMed1993

The plasmid-encoded urease gene cluster of the family Enterobacteriaceae is positively regulated by UreR, a member of the AraC family of transcriptional activators.

Ureolytic clinical isolates of Providencia stuartii, Salmonella spp., and some Escherichia coli strains contain large urease-encoding plasmids. Expression of urease activity from these isolates is induced at least 20-fold by urea. In order to facilitate studies on the regulatory mechanism controlling this urea-inducible expression, the plasmid-encoded urease genes were inserted into the low-copy-number vector pRK415, to form pSEF70. Deletion mutagenesis of pSEF70 demonstrated that between 1.3 and 1.6 kb of DNA upstream of ureD (the first of seven urease genes clustered in an operon-like fashion) was required for a urease-positive phenotype. An open reading frame coding for a 34.1-kDa polypeptide was found in the DNA sequence of this upstream region. This open reading frame has been designated ureR, for urease regulator. A urea-inducible promoter region was identified upstream of ureD. Transcription from this promoter was activated only when ureR was present in trans. The predicted ureR gene product contains a helix-turn-helix motif and shows significant amino acid similarity to the AraC family of transcriptional activators. We conclude that urea-dependent expression from the plasmid-encoded urease gene cluster requires ureR and that ureR codes for a positive regulatory element controlling transcription of at least one essential urease gene, ureD.

Amino Acid Sequence↗
PubMed1993

Proteus mirabilis urease: transcriptional regulation by UreR.

Proteus mirabilis urease catalyzes the hydrolysis of urea, initiating the formation of urinary stones. The enzyme is critical for kidney colonization and the development of acute pyelonephritis. Urease is induced by urea and is not controlled by the nitrogen regulatory system (ntr) or catabolite repression. Purified whole-cell RNA from induced and uninduced cultures of P. mirabilis and Escherichia coli harboring cloned urease sequences was probed with a 4.2-kb BglI fragment from within the urease operon. Autoradiographs of slot blots demonstrated 4.2- and 5.8-fold increases, respectively, in urease-specific RNA upon induction with urea. Structural and accessory genes necessary for urease activity, ureD, A, B, C, E, and F, were previously cloned and sequenced (B. D. Jones and H. L. T. Mobley, J. Bacteriol. 171:6414-6422, 1989). A 1.2-kb EcoRV-BamHI restriction fragment upstream of these sequences confers inducibility upon the operon in trans. Nucleotide sequencing of this fragment revealed a single open reading frame of 882 nucleotides, designated ureR, which is transcribed in the direction opposite that of the urease structural and accessory genes and encodes a 293-amino-acid polypeptide predicted to be 33,415 Da in size. Autoradiographs of sodium dodecyl sulfate-polyacrylamide gels of [35S]methionine-labeled polypeptides obtained by in vitro transcription-translation of the PCR fragments carrying only ureR yielded a single band with an apparent molecular size of 32 kDa. Fragments carrying an in-frame deletion within ureR synthesized a truncated product. The predicted UreR amino acid sequence contains a potential helix-turn-helix motif and an associated AraC family signature and is similar to that predicted for a number of DNA-binding proteins, including E. coli proteins that regulate acid phosphatase synthesis (AppY), porin synthesis (EnvY), and rhamnose utilization (RhaR). These data suggest that UreR governs the inducibility of P. mirabilis urease.

Base Sequence↗
PubMed1994

Single-step purification of Proteus mirabilis urease accessory protein UreE, a protein with a naturally occurring histidine tail, by nickel chelate affinity chromatography.

Proteus mirabilis urease, a nickel metalloenzyme, is essential for the virulence of this species in the urinary tract. Escherichia coli containing cloned structural genes ureA, ureB, and ureC and accessory genes ureD, ureE, ureF, and ureG displays urease activity when cultured in M9 minimal medium. To study the involvement of one of these accessory genes in the synthesis of active urease, deletion mutations were constructed. Cultures of a ureE deletion mutant did not produce an active urease in minimal medium. Urease activity, however, was partially restored by the addition of 5 microM NiCl2 to the medium. The predicted amino acid sequence of UreE, which concludes with seven histidine residues among the last eight C-terminal residues (His-His-His-His-Asp-His-His-His), suggested that UreE may act as a Ni2+ chelator for the urease operon. To exploit this potential metal-binding motif, we attempted to purify UreE from cytoplasmic extracts of E. coli containing cloned urease genes. Soluble protein was loaded onto a nickel-nitrilotriacetic acid column, a metal chelate resin with high affinity for polyhistidine tails, and bound protein was eluted with a 0 to 0.5 M imidazole gradient. A single polypeptide of 20-kDa apparent molecular size, as shown by sodium dodecyl sulfate-10 to 20% polyacrylamide gel electrophoresis, was eluted between 0.25 and 0.4 M imidazole. The N-terminal 10 amino acids of the eluted polypeptide exactly matched the deduced amino acid sequence of P. mirabilis UreE. The molecular size of the native protein was estimated on a Superdex 75 column to be 36 kDa, suggesting that the protein is a dimer. These data suggest that UreE is a Ni(2)+-binding protein that is necessary for synthesis of a catalytically active urease at low Ni(2+) concentrations.

Amino Acid Sequence↗
PubMed2003

Identification and characterization of the nickel uptake system for urease biogenesis in Streptococcus salivarius 57.I.

Ureases are multisubunit enzymes requiring Ni(2+) for activity. The low pH-inducible urease gene cluster in Streptococcus salivarius 57.I is organized as an operon, beginning with ureI, followed by ureABC (structural genes), and ureEFGD (accessory genes). Urease biogenesis also requires a high-affinity Ni(2+) uptake system. By searching the partial genome sequence of a closely related organism, Streptococcus thermophilus LMG18311, three open reading frame (ORFs) homologous to those encoding proteins involved in cobalamin biosynthesis and cobalt transport (cbiMQO) were identified immediately 3' to the ure operon. To determine whether these genes were involved in urease biogenesis by catalyzing Ni(2+) uptake in S. salivarius, regions 3' to ureD were amplified by PCRs from S. salivarius by using primers identical to the S. thermophilus sequences. Sequence analysis of the products revealed three ORFs. Reverse transcriptase PCR was used to demonstrate that the ORFs are transcribed as part of the ure operon. Insertional inactivation of ORF1 with a polar kanamycin marker completely abolished urease activity and the ability to accumulate (63)Ni(2+) during growth. Supplementation of the growth medium with NiCl(2) at concentrations as low as 2.5 micro M partially restored urease activity in the mutant. Both wild-type and mutant strains showed enhanced urease activity when exogenous Ni(2+) was provided at neutral pH. Enhancement of urease activity by adding nickel was regulated at the posttranslational level. Thus, ORF1, ORF2, and ORF3 are part of the ure operon, and these genes, designated ureM, ureQ, and ureO, respectively, likely encode a Ni(2+)-specific ATP-binding cassette transporter.

Cloning, Molecular↗
PubMed1995

Molecular biology of microbial ureases.

Urease (urea amidohydrolase; EC 3.5.1.5) catalyzes the hydrolysis of urea to yield ammonia and carbamate. The latter compound spontaneously decomposes to yield another molecule of ammonia and carbonic acid. The urease phenotype is widely distributed across the bacterial kingdom, and the gene clusters encoding this enzyme have been cloned from numerous bacterial species. The complete nucleotide sequence, ranging from 5.15 to 6.45 kb, has been determined for five species including Bacillus sp. strain TB-90, Klebsiella aerogenes, Proteus mirabilis, Helicobacter pylori, and Yersinia enterocolitica. Sequences for selected genes have been determined for at least 10 other bacterial species and the jack bean enzyme. Urease synthesis can be nitrogen regulated, urea inducible, or constitutive. The crystal structure of the K. aerogenes enzyme has been determined. When combined with chemical modification studies, biophysical and spectroscopic analyses, site-directed mutagenesis results, and kinetic inhibition experiments, the structure provides important insight into the mechanism of catalysis. Synthesis of active enzyme requires incorporation of both carbon dioxide and nickel ions into the protein. Accessory genes have been shown to be required for activation of urease apoprotein, and roles for the accessory proteins in metallocenter assembly have been proposed. Urease is central to the virulence of P. mirabilis and H. pylori. Urea hydrolysis by P. mirabilis in the urinary tract leads directly to urolithiasis (stone formation) and contributes to the development of acute pyelonephritis. The urease of H. pylori is necessary for colonization of the gastric mucosa in experimental animal models of gastritis and serves as the major antigen and diagnostic marker for gastritis and peptic ulcer disease in humans. In addition, the urease of Y. enterocolitica has been implicated as an arthritogenic factor in the development of infection-induced reactive arthritis. The significant progress in our understanding of the molecular biology of microbial ureases is reviewed.

Amino Acid Sequence↗
PubMed1987

Urease testing and yeast taxonomy.

When urease production was assayed by the hydrolysis of [14C]urea, all basidiomycetous yeasts tested, including the Cryptococcus vishniacii complex (previously reported urease negative), produced significant amounts of 14CO2. The Schizosaccharomycetaceae were the only urease-positive ascomycetous yeasts tested. Yarrowia lipolytica was urease negative. The stoichiometry of [14C]urea hydrolysis paralleled by Roberts' rapid urea hydrolysis (RUH) test indicated that causes of anomalous results in conventional urease testing include acidification and alkalinization of the test medium by products of endogenous metabolism and autolysis rather than urease activity. Anomalous results also occurred when cells were grown on media containing the chelating agent ethylenediaminetetraacetic acid (EDTA) prior to RUH. The addition of EDTA to a complex natural medium inhibited urease production in all yeasts reportedly growing at 35 degrees C (and all other yeasts tested), except Filobasidiella (Cr.) neoformans var. neoformans (NIH 12). The RUH test could differentiate at the varietal level: Fil. (Cr.) neoformans var. neoformans was about 10 times more resistant to EDTA in media used for the growth of cells prior to RUH testing than was Fil. neoformans var. bacillispora (Cr. neoformans var. gattii) (NIH 191). Urease production by Fil. neoformans var. bacillispora was specifically restored to half maximal activity by the addition of 22 microM Ni+2 (as NiCl2) to a growth medium containing 0.100 mM EDTA.

Cryptococcus↗
PubMed2004

Low concentration of guanidine hydrochloride induces the formation of an aggregation-prone state in alpha-urease.

Canavalia ensiformis (jack bean) alpha-urease is a hexameric protein characterized by a complex denaturation mechanism. In previous papers, we have shown that a hydrophobic 8-anilino-1-naphthalenesulfonic acid (ANSA) binding conformer could be populated in a moderate concentration of denaturant. This state was obtained under conditions that had no detectable impact on its tertiary structure, as indicated by fluorescence measurements. In the present study, we further characterized this ANSA-binding state in an attempt to understand urease behavior. Evidence presented here shows that the presence of ANSA was not required for the generation of the conformer and that its affinity for ANSA came from an increase in hydrophobicity leading to aggregation. Circular dichroism investigation of urease revealed that it had periodical secondary structure content similar to Klebsiella aerogenes urease (secondary structures calculated on the basis of crystallographic data). The impact of 0.9 M guanidine hydrochloride (GuHCl) on soluble urease secondary structures was minimal but is compatible with a slight increase in beta-sheet structures. Such modification may indicates that aggregation involves amyloid-like fibril formation. Electron microscopy analysis of urease in the absence of GuHCl revealed the presence of urease hexamers (round shape 13 nm in diameter). These particles disappeared in the presence of moderate denaturant concentration owing to the formation of aggregates and fibril-like structures. The fibrils obtained in 1.5 M GuHCl had an average diameter of 6.5 nm, suggesting that urease hexamers dissociated into smaller oligomeric forms when forming such fibrils.

Anilino Naphthalenesulfonates↗
PubMed1980

Jack been urease (EC 3.5.1.5). II. The relationship between nickel, enzymatic activity, and the "abnormal" ultraviolet spectrum. The nickel content of jack beans.

At low pH, EDTA promotes the loss of the tightly bound nickel ions from jack bean urease. The specific activity of soluble enzyme after partial EDTA-promoted inactivation is a linear function of the nickel content. The results are consistent with the presence of 2.0 nickel ions per 97 000-dalton subunit in pure urease. The time scale for loss of enzymatic activity and nickel under these conditions is similar to that for loss of the "abnormal" tail absorption in the ultraviolet and visible absorption spectrum of urease (including the shoulder at approximately 420 nm). This indicates that nickel in urease is essential for enzymatic activity and establishes that the metal ions are in part responsible for the tail absorption in the ultraviolet spectrum of urease. After partial inactivation in the presence of EDTA either at low pH or in 2.5 M guanidinium chloride at neutral pH, urease did not regain activity in the presence of Ni2+. As yet apourease has not been produced reversibly. Jack bean seeds grown hydroponically without added nickel were low in both urease activity and nickel (10 and 6%, respectively, of parent seeds). Several other metal ions were readily available. This result suggests that metal ions other than nickel cannot substitute for nickel in the formation of normally active urease.

Diacetyl↗
PubMed2004

Diagnosis of Helicobacter pylori infection using urease rapid test in patients with bleeding duodenal ulcer: influence of endoscopic signs and simultaneous corporal and antral biopsies.

INTRODUCTION: The sensitivity of invasive diagnostic methods for Helicobacter pylori (H. pylori) infection, particularly of urease rapid test, is decreased in cases of gastroduodenal ulcer and upper gastrointestinal bleeding. OBJECTIVES: To assess the influence of blood in the stomach or recent bleeding endoscopic signs in the diagnostic sensitivity of urease rapid test among patients with bleeding duodenal ulcer, as well as the influence of simultaneously collecting corporal and antral biopsy samples. PATIENTS AND METHODS: 120 patients, 85 male and 35 female, with an average age of 62 (18-88) years, who were admitted to our Hospital due to bleeding duodenal ulcer and who received an endoscopic diagnosis within 24 hours of admission were included. None of the patients had been under treatment with non-steroideal antiinflammatory drugs, proton-pump inhibitors or antimicrobial drugs in the two weeks prior to the bleeding event, and none had received eradicating therapy for H. pylori. In this group of selected patients an H. pylori infection rate nearing 100% was assumed. H. pylori infection was ruled out using antral biopsy (69 cases) or both antral and fundic biopsies (51 cases) for urease rapid testing (Jatrox-H.p.-Test). Patients were classified in three groups according to their endoscopic bleeding signs: a) presence of blood in the stomach or recent bleeding ulcer (21 cases); b) ulcer showing non-recent bleeding signs (38 cases); and c) ulcer without bleeding signs (61 cases). The sensitivity of the urease rapid test was compared between patient groups. Similarly, urease test results with an antral biopsy sample were compared in 100 patients with non-bleeding duodenal ulcer. RESULTS: Urease test was positive in 93% of patients with non-bleeding duodenal ulcer, and in 83% of patients with upper gastrointestinal bleeding, which reached statistical significance (p = 0.019). This test was positive in 82.6% of patients with an antral biopsy, and in 82.3% of patients with combined antral and fundic biopsies. In group A, urease test was positive in 90.5% of patients; in group B, it was positive in 89.5% of patients, and in group C, the test turned positive in 75.4% of patients. Statistical differences were only reached when patients in group C were compared to patients in groups A and B together (p = 0.037). CONCLUSIONS: 1. The presence of either blood in the stomach or recent bleeding endoscopic signs appeared not to be the conditioning factor for the decreased sensitivity of urease test among patients with bleeding duodenal ulcer. 2. The decreased sensitivity of this test in patients with upper gastrointestinal bleeding is more evident during the resolution stage, and it does not seem to occur because of H. pylori migration from the antrum to the corporal gastric region.

Adolescent↗
PubMedDate not supplied

Effect of Azospirillum brasilense inoculation on urease activity in soil and gamma-sterilized soil.

Azospirillum spp. is considered a PGPR (plant growth promoting rhyzobacteria) bacterium, besides this interest, there is little information about its effects on other functional microbial groups or on soil enzymes. In this paper, the impact that A. brasilense 7001 inoculation has on urease activity expression in a Typic Argiudoll was studied. Evolution of urease activity of soil and of gamma-irradiation (25 KGy) sterilized soil, and the inoculated strain survival were tested. The relation between soil urease activity and soil NH4(+)-N was also determined. In gamma-sterilized soil, urease activity of inoculated soil increased with time, showing significant differences with regard to the control soil without inoculum at day 15. In non-sterile soil, urease activity decreased during the studied period in all treatments; in inoculated soil, it showed higher or lower values than the control depending on sampling time. Azospirillum survival was important and different according to soil conditions. The negative relation between NH4(+)-N concentration and soil urease activity (r2 = 0.62) was not observed in inoculated soil. The role of the addition of autoclaved inoculum in the urease activity expression is discussed. The research proves that in both studied situations Azospirillum modified soil urease activity, and that the competition with native microorganisms and soil NH4(+)-N may affect this bacterium capacity.

Azospirillum brasilense↗
PubMed1991

Helicobacter pylori urease: properties and role in pathogenesis.

Urease (urea amidohydrolase, EC 3.5.1.5) catalyzes the hydrolysis of urea to yield ammonia and carbon dioxide. Research on this enzyme has gained momentum since the discovery of Helicobacter pylori as a causative agent of human gastritis. The remarkably high urease activity of each organism has served as the basis of diagnostic tests for the presence of the organism in the urease biopsy test and urea breath test. Urease undoubtedly plays a central role in H. pylori pathogenesis. Hydrolysis of urea with generation of ammonia may enable survival of this acid-sensitive organism in the gastric mucosa. Ammonia generated by urea hydrolysis may also produce severe cytotoxic effects within gastric epithelium. The enzyme also elicits a strong immune response during acute infection, suggesting that this abundant antigen is readily available to the immune system. An increase in serum IgG titer is predictive of ongoing infection. Much progress has been made with regard to the molecular biology of urease. The high molecular weight protein (estimated by several investigators to be 300-520 kDa) has been purified, revealing two distinct subunits of 29.5 kDa and 66 kDa, a unique subunit structure as compared with other microbial ureases. However, amino acid sequences are nevertheless well conserved when compared with other bacterial ureases and that of the jack bean, Canavalia ensiformis. Furthermore, genes encoding urease of H. pylori have been cloned, sequenced, and amplified by the polymerase chain reaction.

Animals↗
PubMedDate not supplied

[Properties of urease immobilized on the functional organic silica surface].

The paper deals with kinetics of the urea hydrolysis by microbial-origin urease dissolved and immobilized on the organic silica surface. It is shown that hydrolysis kinetics for soluble urease is described by the Michaelis-Menten equation until the concentration of urea reaches 1 M. Two fractions differing in the Michaelis constant are revealed for silochrome immobilized urease. The rate of urea hydrolysis by native and immobilized urease was studied depending on the pH value in presence of the substrate in the 1 M and 5 mM concentration. The hydrolysis rate of 1 M urea in the buffer-free solution by silochrome-immobilized urease is practically independent of pH within 4.5-6.5. Application of a 2.5 mM phosphate-citrate buffer as a solvent causes an increase in the hydrolysis rate within this pH range. For a soluble urease the 1 M urea hydrolysis rate dependence on pH is ordinary at pH 5.8-6.0. If the substrate concentration is 5 mM, the pH-dependences for the rate of the urea hydrolysis by silochrome- and aerosil-immobilized urease are close and at pH above 6.0 coincide with those for a soluble enzyme. The found differences in the properties of soluble and immobilized ureases are explained by the substrate and reaction products diffusion.

Enzymes, Immobilized↗
PubMed1997

Gastric juice urease activity as a diagnostic test for Helicobacter pylori infection.

OBJECTIVE: An ideal assay (inexpensive, sensitive, specific, and readily available) for Helicobacter pylori is lacking. Urease activity is an important characteristic of the organism and is employed in the rapid urease and urea breath tests. In this study, we assessed whether a simpler test, namely, measurement of gastric juice urease activity, would provide comparable results. METHODS: Gastric juice was analyzed for urea and ammonia in 57 patients evaluated with rapid urease test and histology. Urease activity was assessed by the fraction of urea hydrolyzed to ammonia. RESULTS: Thirty-five subjects were H. pylori positive and 22 were H. pylori negative. Compared with noninfected subjects, H. pylori-positive patients had lower urea levels (0.52 +/- 0.10 vs. 2.77 +/- 0.48 mM, p < 0.01), higher ammonia concentrations (6.59 +/- 1.06 vs. 1.64 +/- 0.25 mM, p < 0.01), and higher gastric urease activity (0.83 +/- 0.03 vs. 0.24 +/- 0.14, p < 0.01). In H. pylori-negative patients, there was a correlation between blood and gastric urea (r = 0.61, p < 0.01). However, in H. pylori-positive patients, no such relationship existed (r = 0.30, p = 0.11). The ratio of gastric to blood urea was lower in infected patients (0.11 +/- 0.02 vs. 0.45+/- 0.04, p < 0.01). The sensitivity and specificity of gastric urease activity for diagnosis of H. pylori were 91% and 100%, respectively, and for the ratio of gastric to blood urea, 89% and 95%, respectively. CONCLUSION: Gastric juice urease activity is a simple, sensitive, and specific means to detect H. pylori.

Ammonia↗
PubMed1966

Purification and Properties of Urease Derived from Hydrated Seeds of Jack Bean, Canavalia ensiformis (L) DC.

Urease from jack bean meal and hydrated seeds has been obtained in 25 to 33% yield with specific activity in the range of 1000 to 1070 units/mg protein. A purification of 100 to 130-fold was achieved from meal and fully soaked seeds. Use of beta-mercaptoethanol and EDTA was found essential to obtain this high yield and purity. Amino acid analysis showed all 18 amino acids commonly found in proteins. Electrophoresis of urease from soaked seeds (specific activity: 1025 units/mg protein) on a starch-gel block showed 2 peaks. Upon ultracentrifugation of urease samples having a low specific activity (less than 25% pure), the major portion of the urease was probably present in a peak having a sedimentation value of 11 to 12. With relatively pure samples (55-100% pure). S values in the range of 18 to 20 and 24 to 26 were obtained. Usually the purest samples of urease tested without any prior storage lacked the 24 to 26 S peak or the higher polymeric forms. The percentage areas under none of the ultracentrifuge peaks corresponded to the percentage purity of the sample analyzed. It is argued that the physical state of urease in the cell when associated with other seed proteins is as yet uncertain. In crude extracts, a portion of urease exists in a 12 S form but so far data on its origin and specific activity in relation to other species of urease are not available.

Journal Article↗
PubMed1981

Resistance to acetohydroxamate acquired by slow adaptive increases in urease in cultured tobacco cells.

Urease activity of tobacco XD cells (1U cells) had undergone a 4-fold increase (4U cells) during a year of growth on urea (Skokut and Filner 1980 Plant Phvsiol 65: 995-1003). A clone of 4U cells gave rise to 12U cells during another year of growth on urea. The doubling time of 12U cells on urea is 2.2 days, compared to about 4 days for 1U cells, while 1U and 12U cells double in 2 days on nitrate. Acetohydroxamic acid (AHA), a specific inhibitor/reversible inactivator of jack bean urease, affects tobacco cell urease similarly. Fifty per cent inhibition of growth by AHA occurred at 20 micromolar in 1U cells growing on urea and at 165 micromolar in 12U cells growing on urea, but at 600 micromolar for either 1U or 12U cells growing on nitrate. When 12U cells were grown on urea with 100 micromolar AHA, extractable urease activity decreased 80% within 2.5 hours and remained at this level for 2 weeks; the doubling time increased to 3.7 days, and intracellular urea rose 2-fold, compared to 12U cells grown on urea without AHA. Urease of 12U cells inactivated by AHA in vivo could be reactivated to its pre-AHA level by incubation at 30 C after extraction and separation from free AHA. AHA inhibited incorporation of (15)N from [(15)N]urea into Kjeldahl nitrogen in the cells, in spite of the increased intracellular urea. These results indicate that AHA acts primarily by inhibiting urease action, rather than by inhibition of formation of urease protein or of uptake of urea. Because 12U cells are 8 times more tolerant of AHA than 1U cells, it is likely that growth on urea in the presence of AHA should select strongly for cells with high urease.

Journal Article↗