Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.5.1.5 (urease)
 7,257 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Hydroxyurea has emerged as a new therapy for sickle cell disease but a complete mechanistic description of its beneficial actions does not exist. Patients taking hydroxyurea show evidence for the in vivo conversion of hydroxyurea to nitric oxide (NO), which also has drawn interest as a sickle cell disease treatment. While the chemical oxidation of hydroxyurea produces NO or NO-related products, NO formation from the reactions of hydroxyurea and hemoglobin do not occur fast enough to account for the observed increases in patients taking hydroxyurea. Both horseradish peroxidase and catalase catalyze the rapid formation of nitric oxide and nitroxyl (HNO) from hydroxyurea. In these reactions, hydroxyurea is converted to an acyl nitroso species that hydrolyzes to form HNO. The ferric heme protein then oxidizes HNO to NO that combines with the heme iron to form a ferrous-NO complex that may act as an NO donor. In general, acyl nitroso compounds, regardless of the method of their preparation, hydrolyze to form HNO and the corresponding carboxylic acid derivative. Similarly, the incubation of blood and hydroxyurea with urease rapidly form NO-related species suggesting the initial urease-mediated hydrolysis of hydroxyurea to hydroxylamine, which then reacts quickly with hemoglobin to form these products. These studies present two NO releasing mechanisms from hydroxyurea that are kinetically competent with clinical observations.
 ...
PMID:N-hydroxyurea and acyl nitroso compounds as nitroxyl (HNO) and nitric oxide (NO) donors. 1610 27

Two important metal-responsive regulators, NikR and Fur, are involved in nickel and iron homeostasis and controlling gene expression in Helicobacter pylori. To date, they have been implicated in the regulation of sets of overlapping genes. We have attempted here dissection of the molecular mechanisms involved in transcriptional regulation of the NikR and Fur proteins, and we investigated protein-promoter interactions of the regulators with known target genes. We show that H. pylori NikR is a tetrameric protein and, through DNase I footprinting analysis, we have identified operators for NikR to which it binds with different affinities in a metal-responsive way. Mapping of the NikR binding site upstream of the urease promoter established a direct role for NikR as a positive regulator of transcription and, through scanning mutagenesis of this binding site, we have determined two subsites that are important for the binding of the protein to its target sequence. Furthermore, by alignment of the operators for NikR, we have shown that the H. pylori protein recognizes a sequence that is distinct from its well-studied orthologue in Escherichia coli. Moreover, we show that NikR and Fur can bind independently at distinct operators and also compete for overlapping operators in some coregulated gene promoters, adding another dimension to the previous suggested link between iron and nickel regulation. Finally, the importance of an interconnection between metal-responsive gene networks for homeostasis is discussed.
 ...
PMID:In vitro analysis of protein-operator interactions of the NikR and fur metal-responsive regulators of coregulated genes in Helicobacter pylori. 1626 95

The effectiveness of two amendments for the in situ remediation of a Cd- and Ni-contaminated soil in the Louis Fargue long-term field experiment was assessed. In April 1995, one replicate plot (S1) was amended with 5% w/w of beringite (B), a coal fly ash (treatment S1+B), and a second plot with 1% w/w zerovalent-Fe iron grit (SS) (treatment S1+SS), with the aim of increasing metal sorption and attenuating metal impacts. Long-term responses of daily respiration rates, microbial biomass, bacterial species richness and the activities of key soil enzymes (acid and alkaline phosphatase, arylsulfatase, beta-glucosidase, urease and protease activities) were studied in relation to soil metal extractability. Seven years after initial amendments, the labile fractions of Cd and Ni in both the S1+B and S1+SS soils were reduced to various extents depending on the metal and fractions considered. The soil microbial biomass and respiration rate were not affected by metal contamination and amendments in the S1+B and S1+SS soils, whereas the activity of different soil enzymes was restored. The SS treatment was more effective in reducing labile pools of Cd and Ni and led to a greater recovery of soil enzyme activities than the B treatment. Bacterial species richness in the S1 soil did not alter with either treatment. It was concluded that monitoring of the composition and activity of the soil microbial community is important in evaluating the effectiveness of soil remediation practices.
 ...
PMID:Biochemical parameters and bacterial species richness in soils contaminated by sludge-borne metals and remediated with inorganic soil amendments. 1651 62

Ferrimagnetic materials can be expected to be useful as thermal seeds for hyperthermic treatment of cancer, especially where the cancer is located in deep parts of body, as they can generate heat by magnetic hysteretic loss when they are placed in an alternating magnetic field. In this study, hollow magnetite (Fe(3)O(4)) particles were prepared using an enzymatic reaction of urease. A hollow particle was obtained by using a Pasteur pipette. The particle was 500 microm in size and was composed of Fe(3)O(4). Its saturation magnetization and coercive force were 57 emuxg(-1) and 183 Oe, respectively. Its heat generation under an alternating magnetic field of 300 Oe at 100 kHz was estimated to be 45 Wxg(-1). Microspheres 30 microm in diameter were also successfully obtained by using a spray gun.
 ...
PMID:Enzymatic preparation of hollow magnetite microspheres for hyperthermic treatment of cancer. 1677 May 44

Maintaining metal homeostasis is crucial for the adaptation of Helicobacter pylori to the gastric environment. Iron, copper, and nickel homeostasis has recently been demonstrated to be required for the establishment of H. pylori infection in animal models. Here we demonstrate that the HP0969-0971 gene cluster encoding the Czc-type metal export pump homologs HP0969, HP0970, and the H. pylori-specific protein HP0971 forms part of a novel H. pylori metal resistance determinant, which is required for gastric colonization and for the modulation of urease activity. Insertional mutagenesis of the HP0971, HP0970, or HP0969 genes in H. pylori reference strain 26695 resulted in increased sensitivity to cadmium, zinc, and nickel (czn), suggesting that the encoded proteins constitute a metal-specific export pump. Accordingly, the genes were designated cznC (HP0971), cznB (HP0970), and cznA (HP0969). The CznC and CznA proteins play a predominant role in nickel homeostasis, since only the cznC and cznA mutants but not the cznB mutant displayed an 8- to 10-fold increase in urease activity. Nickel-specific affinity chromatography demonstrated that recombinant versions of CznC and CznB can bind to nickel and that the purified CznB protein interacted with cadmium and zinc, since both metals competitively inhibited nickel binding. Finally, single cznA, cznB, and cznC mutants did not colonize the stomach in a Mongolian gerbil-based animal model. This demonstrates that the metal export functions of H. pylori cznABC are essential for gastric colonization and underlines the extraordinary importance of metal ion homeostasis for the survival of H. pylori in the gastric environment.
 ...
PMID:The novel Helicobacter pylori CznABC metal efflux pump is required for cadmium, zinc, and nickel resistance, urease modulation, and gastric colonization. 1679 Jul 56

Proteus mirabilis has been described as an aetiological agent in a wide range of infections, playing an important role in urinary tract infections (UTIs). In this study, a collection of P. mirabilis isolates obtained from clinical and non-clinical sources was analysed in order to determine a possible correlation between origin, virulence factors and in vivo infectivity. Isolates were characterized in vitro, assessing several virulence properties that had been previously associated with P. mirabilis uropathogenicity. Swarming motility, urease production, growth in urine, outer-membrane protein patterns, ability to grow in the presence of different iron sources, haemolysin and haemagglutinin production, and the presence and expression of diverse fimbrial genes, were analysed. In order to evaluate the infectivity of the different isolates, the experimental ascending UTI model in mice was used. Additionally, the Dienes test and the enterobacterial repetitive intergenic consensus (ERIC)-PCR assay were performed to assess the genetic diversity of the isolates. The results of the present study did not show any correlation between distribution of the diverse potential urovirulence factors and isolate source. No significant correlation was observed between infectivity and the origin of the isolates, since they all similarly colonized the urinary tract of the challenged mice. Finally, all isolates showed unique ERIC-PCR patterns, indicating that the isolates were genetically diverse. The results obtained in this study suggest that the source of P. mirabilis strains cannot be correlated with pathogenic attributes, and that the distribution of virulence factors between isolates of different origins may correspond to the opportunistic nature of the organism.
 ...
PMID:Proteus mirabilis isolates of different origins do not show correlation with virulence attributes and can colonize the urinary tract of mice. 1680 88

Although comprising less than 0.01% of the normal human gastrointestinal microbiota, Bilophila wadsworthia is the third most common anaerobe recovered from clinical material obtained from patients with perforated and gangrenous appendicitis. Since its discovery in 1988, B. wadsworthia has been recovered from clinical specimens associated with a variety of infections, including sepsis, liver abscesses, cholecystitis, Fournier's gangrene, soft tissue abscesses, empyema, osteomyelitis, Bartholinitis, and hidradenitis suppurativa. In addition, it has been found in the saliva and vaginal fluids of asymptomatic adults and even in the periodontal pockets of dogs. The organism is a saccharolytic, fastidious, and is easily recognized by its strong catalase reaction with 15% H2O2, production of hydrogen sulfide, and growth stimulation by bile (oxgall) and pyruvate. Approximately 75% of strains are urease positive. When grown on pyruvate-containing media, > 85% of strains demonstrate beta-lactamase production. Ribosomal RNA-based phylogenetic studies show Bilophila to be a homogeneous species, most closely related to Desulfovibrio species. Both adherence to human cells and endotoxin have been observed, and preliminary work suggests that environmental iron has a role in expression of outer membrane proteins. Penicillin-binding proteins appear to mediate the organism's susceptibility to at least some beta-lactam agents, which induce spheroplast formation that results in a haze of growth on agar dilution susceptibility test plates which is difficult to interpret. Bilophilastrains are inhibited in vitro by most antibiotics.
 ...
PMID:Bilophila wadsworthia: a unique Gram-negative anaerobic rod. 1688 67

The transition metal nickel plays an important role in gastric colonization and persistence of the important human pathogen Helicobacter pylori, as it is the cofactor of the abundantly produced acid resistance factor urease. Nickel uptake through the inner membrane is mediated by the NixA protein, and the expression of NixA is controlled by the NikR regulatory protein. Here we report that NikR also controls the nickel-responsive expression of the FecA3 (HP1400) and FrpB4 (HP1512) outer membrane proteins (OMPs), as well as the nickel-responsive expression of an ExbB-ExbD-TonB system, which may function in energization of outer membrane transport. Transcription and expression of the frpB4 and fecA3 genes were repressed by nickel in wild-type H. pylori 26695, but they were independent of nickel and derepressed in an isogenic nikR mutant. Both the frpB4 and fecA3 genes were transcribed from a promoter directly upstream of their start codon. Regulation by NikR was mediated via nickel-dependent binding to specific operators overlapping either the +1 or -10 sequence in the frpB4 and fecA3 promoters, respectively, and these operators contained sequences resembling the proposed H. pylori NikR recognition sequence (TATWATT-N(11)-AATWATA). Transcription of the HP1339-1340-1341 operon encoding the ExbB2-ExbD2-TonB2 complex was also regulated by nickel and NikR, but not by Fur and iron. In conclusion, H. pylori NikR controls nickel-responsive expression of the HP1400 (FecA3) and HP1512 (FrpB4) OMPs. We hypothesize that these two NikR-regulated OMPs may participate in the uptake of complexed nickel ions and that this process is energized by the NikR-regulated ExbB2-ExbD2-TonB2 system, another example of the specific adaptation of H. pylori to the gastric lifestyle.
 ...
PMID:NikR mediates nickel-responsive transcriptional repression of the Helicobacter pylori outer membrane proteins FecA3 (HP1400) and FrpB4 (HP1512). 1701 56

Chronic infection of the human stomach by Helicobacter pylori leads to a variety of pathological sequelae, including peptic ulcer and gastric cancer, resulting in significant human morbidity and mortality. Several genes have been implicated in disease related to H. pylori infection, including the vacuolating cytotoxin and the cag pathogenicity island. Other factors important for the establishment and maintenance of infection include urease enzyme production, motility, iron uptake, and stress response. We utilized a C57BL/6 mouse infection model to query a collection of 2,400 transposon mutants in two different bacterial strain backgrounds for H. pylori genetic loci contributing to colonization of the stomach. Microarray-based tracking of transposon mutants allowed us to monitor the behavior of transposon insertions in 758 different gene loci. Of the loci measured, 223 (29%) had a predicted colonization defect. These included previously described H. pylori virulence genes, genes implicated in virulence in other pathogenic bacteria, and 81 hypothetical proteins. We have retested 10 previously uncharacterized candidate colonization gene loci by making independent null alleles and have confirmed their colonization phenotypes by using competition experiments and by determining the dose required for 50% infection. Of the genetic loci retested, 60% have strain-specific colonization defects, while 40% have phenotypes in both strain backgrounds for infection, highlighting the profound effect of H. pylori strain variation on the pathogenic potential of this organism.
 ...
PMID:Identification of Helicobacter pylori genes that contribute to stomach colonization. 1710 54

Persistent colonization of mucosal surfaces by bacteria in the mammalian host requires concerted expression of colonization factors, depending on the environmental conditions. Helicobacter hepaticus is a urease-positive pathogen that colonizes the intestinal and hepatobiliary tracts of rodents. Here it is reported that urease expression of H. hepaticus is iron repressed by the transcriptional regulator Fur. Iron restriction of growth medium resulted in a doubling of urease activity in wild-type H. hepaticus strain ATCC 51449 and was accompanied by increased levels of urease subunit proteins and ureA mRNA. Insertional inactivation of the fur gene abolished iron-responsive repression of urease activity, whereas inactivation of the perR gene did not affect iron-responsive regulation of urease activity. The iron-responsive promoter element was identified directly upstream of the H. hepaticus ureA gene. Recombinant H. hepaticus Fur protein bound to this ureA promoter region in a metal-dependent matter, and binding resulted in the protection of a 41-bp, Fur box-containing operator sequence located at positions -35 to -75 upstream of the transcription start site. In conclusion, H. hepaticus Fur controls urease expression at the transcriptional level in response to iron availability. This represents a novel type of urease regulation in ureolytic bacteria and extends the already diverse regulatory repertoire of the Fur protein.
 ...
PMID:Iron-responsive repression of urease expression in Helicobacter hepaticus is mediated by the transcriptional regulator Fur. 1710 56


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>