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At least 595 records · Page 33Linked to original sources
PubMed1998

Cloning of the nitrate reductase gene of Stagonospora (Septoria) nodorum and its use as a selectable marker for targeted transformation.

The nitrate reductase gene (NIA1) of the phytopathogenic fungus Stagonospora (Septoria) nodorum has been cloned from a cosmid library by homologous hybridisation with a PCR-generated probe. A 6. 7-kb fragment carrying the NIA1 gene was subcloned and partially characterised by restriction mapping. Sequencing of the gene indicated a high degree of homology, both at the nucleotide and amino-acid levels, with nitrate reductase genes of other filamentous fungi. Furthermore, consensus regulatory signals thought to be involved in the control of nitrogen metabolism are present in the 5' flanking region. The cloned NIA1 gene has been used to develop a gene-transfer system based on nitrate assimilation. Stable nia1 mutants of S. nodorum defective in nitrate reductase were isolated by virtue of their resistance to chlorate. These were transformed back to nitrate utilisation with the wild-type S. nodorum NIA1 gene. Southern analyses revealed that transformation occurred as a result of the integration of transforming DNA into the fungal genome; in all cases examined, integration was targeted to the homologous sequence.

Amino Acid Sequence↗
PubMed2000

Death caused by a letter bomb.

A 48-year-old man was killed by the explosion of a letter bomb after receiving severe injuries to his face and left hand. The autopsy ascertained that the right eye and orbit had been completely destroyed by a large piece of metal from a tin can that had entered the cranial cavity through the right eye and caused fatal brain damage. The victim had also sustained a severe injury to his left hand. Reconstruction of the metal and plastic fragments showed that the victim had received a padded envelope with a video cassette in which a simple explosive device was hidden in a flat tin. The explosive charge consisted of a mixture (ca. 60 g) of sodium chlorate, sodium chloride and sucrose. The charge was detonated by a nylon cord attached to the inside of the envelope which was stretched when the video cassette was pulled out of the envelope. This removed a piece of plastic from between two contacts, and the explosion was set off immediately by a battery which activated two flash bulbs placed within the charge.

Autopsy↗
PubMed2001

Chlorite dismutase from Ideonella dechloratans.

Chlorite dismutase has been purified from the chlorate-metabolizing bacterium Ideonella dechloratans. The purified enzyme is tetrameric, with a relative molecular mass of 25,000 for the subunit, and contains about 0.6 heme/subunit as isolated. Its catalytic properties are similar, but not identical, to those found for a similar enzyme purified earlier from the bacterium GR-1. The heme group in Ideonella chlorite dismutase is readily reduced by dithionite, in contrast to the GR-1 enzyme, and redox titration gave a value of -21 mV for the midpoint potential at pH 7. The heme group has been characterized by optical and EPR spectroscopy. It is high-spin ferric at neutral pH, with spectroscopic properties similar to those found for cytochrome c peroxidase. In the alkaline pH range, a low-spin compound is formed. A 22-residue N-terminal amino acid sequence has been determined and no homologue has been found in the protein sequence databases.

Amino Acid Sequence↗
PubMed1998

Topography of amphiregulin expression in cultured human keratinocytes: colocalization with the epidermal growth factor receptor and CD44.

Much of the autonomous growth of cultured keratinocytes is attributable to the signaling of amphiregulin, a heparin-binding autocrine growth factor, through the epidermal growth factor receptor. Emerging evidence suggests, moreover, that the membrane proteoglycan, CD44, is a cofactor for the interaction of heparin-binding ligands with their receptors. This model was evaluated by characterizing the patterns of the immunolabeled molecules in cultured human neonatal keratinocytes, to test the hypothesis that involvement in a common function results in coordinate segregation within or on the cell. The molecules were localized by double immunofluorescence labeling to detect amphiregulin and either the epidermal growth factor receptor or CD44, and the immunostained products were imaged by scanning laser confocal microscopy. Both amphiregulin and the epidermal growth factor receptor segregated to a perinuclear distribution and to intercellular contacts. In addition, amphiregulin localized to the outer leading edge of colonies and focally to intranuclear sites. Metabolic blockade of proteoglycan sulfation with sodium chlorate inhibited growth of the cells and concurrently enhanced the nuclear, but decreased the outer leading edge, labeling for amphiregulin. There was no nuclear or perimeter labeling for the epidermal growth factor receptor. Cultures co-immunolabeled for CD44 and amphiregulin exhibited variable perinuclear staining for both, but otherwise CD44 was distributed to intercellular contacts. The intercellular localizations of CD44 with amphiregulin and of amphiregulin with the epidermal growth factor receptor were strongly concordant. These data are consistent with a concerted function at intercellular contacts, where cytokine signaling is mediated via receptor binding and possibly regulated by the CD44 proteoglycan as cofactor. The intranuclear and perimeter labeling of amphiregulin, however, suggests that this cytokine has additional functions, both in the nucleus and as a matrix receptor.

Amphiregulin↗
PubMed1991

Purification and properties of a dissimilatory nitrate reductase from Haloferax denitrificans.

A membrane-bound nitrate reductase (nitrite:(acceptor) oxidoreductase, EC 1.7.99.4) from the extremely halophilic bacterium Haloferax denitrificans was solubilized by incubating membranes in buffer lacking NaCl and purified by DEAE, hydroxylapatite, and Sepharose 6B gel filtration chromatography. The purified nitrate reductase reduced chlorate and was inhibited by azide and cyanide. Preincubating the enzyme with cyanide increased the extent of inhibition which in turn was intensified when dithionite was present. Although cyanide was a noncompetitive inhibitor with respect to nitrate, nitrate protected against inhibition. The enzyme, as isolated, was composed of two subunits (Mr 116,000 and 60,000) and behaved as a dimer during gel filtration (Mr 380,000). Unlike other halobacterial enzymes, this nitrate reductase was most active, as well as stable, in the absence of salt.

Cell Membrane↗
PubMed1995

Binding to heparan sulfate is a major event during catabolism of lipoprotein lipase by HepG2 and other cell cultures.

Lipoprotein lipase (LPL) is rapidly and efficiently cleared from the circulation by the liver through an as yet unclear mechanism. In the present study, we determined the nature of LPL interactions with the liver parenchimal cell line HepG2 as compared to other cells in culture. Binding, cell association and degradation of 125I-labelled bovine milk LPL by HepG2 cells, normal and low density lipoprotein (LDL) receptor-negative human fibroblasts and Chinese hamster ovary (CHO) cells show similar values irrespective of source and origin. LPL metabolism in HepG2 cells was characterized by a high capacity to degrade the enzyme, an extremely high sensitivity to heparin and was inhibited by 60%-70% after treatment of the cells with sodium chlorate and heparinase (but not chondroitinase). These findings suggested an important role for heparan sulfate in the process of cell interaction and metabolism of LPL. To further clarify the role of heparan sulfate in determining the LPL-cell interactions, we compared the metabolism of LPL in wild type and mutant heparan sulfate-deficient CHO cells. Heparan sulfate-deficient CHO cells show a low capacity to bind and degrade LPL, about 10%-20% that of the wild type cells. In another set of experiments, we sought to determine whether LPL interactions with HepG2 cells are affected by triglyceride-rich lipoproteins. The results clearly show that whereas unlabeled LPL dramatically enhanced the metabolism of radioiodinated very low density lipoprotein (VLDL), unlabeled VLDL had no effect on radioiodinated LPL metabolism in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Analysis of oxyhalide disinfection by-products and other anions of interest in drinking water by ion chromatography.

The US Environmental Protection Agency is developing regulations for various drinking water disinfection by-products (DBPs). This effort involves developing analytical methods for the DBPs formed as a result of different disinfection treatments and collecting occurrence data for these species. Ion chromatography is one method being used to analyze drinking water samples for the following inorganic DBPs: chlorite, chlorate and bromate. These anions, however, are difficult to separate from common interfering anions of chloride, carbonate and nitrate. A method is therefore presented by which tetraborate/boric acid is used to separate these anions. Method detection limits of the order of 10 micrograms/l, using conductivity and UV detection were obtained. Stability studies of chlorite showing the effectiveness of ethylenediamine as a preservative and summary data for an occurrence of nitrite, nitrate and the DBP precursor bromide are presented.

Anions↗
PubMed1980

Biochemical, cellular and developmental characterization of a temperature-sensitive mutant of Nicotiana tabacum and its second site revertant.

We have analyzed a temperature-sensitive mutant, ts4, of Nicotiana tabacum, together with its newly isolated second revertant, Rt1, both in cell culture and as a regenerated plant. Cells of the temperature-sensitive mutant will grow only below 30 degrees C, whereas the revertant can grow at temperatures above that but not at those as high as will wild-type cells. Enzyme assays of phenylalanine ammonia lyase and nitrate reductase showed that ts4 had substantial increases and decreases, respectively. The revertant resembled ts4 for these activities. The decrease in nitrate reductase is associated with resistance of ts4 to a pulse of chlorate that kills wild-type. Amino acid and polyamine analyses showed that ornithine levels rise in ts4 during 24 hr at the high temperature, while spermine and spermidine levels fall. The ts4 mutant has low levels of ornithine decarboxylase activity and s-adnosyl-methionine decarboxylase activity, whereas the revertant has restored levels of only ornithine decarboxylase. This is the only enzyme activity in which Rt1 resembles wild-type more than it resembles ts4, suggesting that it is the site of metabolic alteration of the mutation. In regenerated plants, ts4 has a low chlorophyll content, while the revertant has a fully restored chlorophyll content. Flowers on the revertant plant are both male and female sterile, with the male sterility associated with anthers converted into petals. The correlations among these ts4 and Rt1 alterations demonstrate novel regulatory interactions between nitrate reductase and the two decarboxylase enzymes, and also suggest that we have partially unravelled the molecular basis for a particular developmental endpoint.

Adenosylmethionine Decarboxylase↗
PubMed1993

The herbicide sensitivity gene CHL1 of Arabidopsis encodes a nitrate-inducible nitrate transporter.

This paper reports the identification and functional expression of a gene that is involved in nitrate uptake in plants, a process essential for the assimilation of nitrate and the biological removal of nitrate from the soil solution. The CHL1 gene of Arabidopsis, which when mutated confers resistance to the herbicide chlorate and a decrease in nitrate uptake, was isolated and found to encode a protein with 12 putative membrane-spanning segments. Injection of CHL1 mRNA into Xenopus oocytes produces a nitrate- and pH-dependent membrane depolarization, inward current, and nitrate uptake. These data show that the CHL1 gene encodes an electrogenic nitrate transporter. CHL1 mRNA is found predominantly in roots and displays nitrate- and pH-dependent regulation.

Amino Acid Sequence↗
PubMed1987

Involvement of a protein with molybdenum cofactor in the in vitro activation of nitrate reductase from a chlA mutant of Escherichia coli K12.

Chlorate-resistant mutants are pleiotropically defective in molybdoenzyme activities. The inactive derivative of the molybdoenzyme, respiratory nitrate reductase (nitrite: (acceptor) oxidoreductase, EC 1.7.99.4), which is present in cell-free extracts of chlA mutants can be activated by addition of purified protein PA, the presumed active product of the chlA+ locus, but the activity of the purified protein PA is low, since comparatively large amounts of protein PA are required for the activation. Addition of 10 mM tungstate to the growth medium of a chlBchlC double mutant leads to inactivation of both the molybdenum cofactor and protein PA. Protein PA prepared from such cells was unable to potentiate the in vitro activation of nitrate reductase present in the soluble fraction of a chlA mutant. Quantitation of inactive protein PA was determined immunologically using protein PA-specific antiserum. When a heat-treated extract of a wild-type strain was added to purified protein PA or to the supernatant fraction of a chlBchlC double mutant grown with tungstate, a large stimulation in the ability of these preparations to activate chlA nitrate reductase was found. We equate the activator of protein PA with molybdenum cofactor because: (1) both are absent from heated extracts of tungstate-grown chlBchlC double mutant and cofactor defective chlA and chlE mutants; (2) both are present in heated extracts of wild-type strain; and (3) they behave identically on molecular-sieve columns.

Coenzymes↗
PubMed1991

Slaughter pigs and pork as a source of human pathogenic Yersinia enterocolitica.

Pathogenic Yersinia enterocolitica strains (serogroups 0:3;0:9 and 0:5.27) were isolated from 36 (42%) of 86 porcine tonsils, 8 (20%) of 40 tongues, 17 (17%) of 100 rectal swabs and from 4 (1%) of 400 pork samples. Pathogenic Yersinia strains were not isolated from samples of 210 pig carcasses and from 20 samples of porcine head meat. These results confirm that pigs are an important reservoir of pathogenic Y. enterocolitica. However, contamination of carcasses during the slaughtering process with Yersinia from either faecal material or from the tonsillary region does not seem to occur frequently and this may also explain the low contamination rate of pathogenic Y. enterocolitica found for pork. For the isolation of pathogenic Y. enterocolitica strains from foods, enrichment in irgasan-ticarcillin-chlorate broth (ITC) and isolation on SS-deoxycholate-calcium agar (SSDC) is recommended.

Animals↗
PubMed1992

Isolation of Yersinia enterocolitica from foods.

Many selective enrichment and plating media for the isolation of Yersinia enterocolitica from foods are described. However, at present no single isolation procedure is available for the recovery of all pathogenic strains of Yersinia enterocolitica. Cold enrichment in phosphate-buffered saline plus 1% sorbitol and 0.15% bile salts (PBSSB) and two-step enrichment with tryptone soy broth (TSB) and bile oxalate sorbose (BOS) broth are very efficient methods for the recovery of a wide spectrum of serotypes of Y. enterocolitica. Enrichment in irgasan ticarcillin chlorate (ITC) broth was found to be the most efficient method for the recovery of strains of serotype 0:3, which is the most common clinical serotype of Y. enterocolitica in Europe. Post-enrichment alkali treatment often results in higher isolation rates. Cefsulodin irgasan novobiocin (CIN) agar and Salmonella-Shigella deoxycholate calcium chloride (SSDC) agar are the most commonly used plating media. For the recovery of serotype 0:8 strains, the common clinical isolates in North America, enrichment in BOS and plating on CIN seems the most efficient procedure. Selection of the proper enrichment procedure will depend on the bio/serotypes of Yersinia spp. sought and on the type of food to be examined. The use of more than one medium for both enrichment and plating will result in higher recovery rates of Yersinia spp. from foods. Parallel use of the following two isolation procedures is recommended. (1) Enrichment in ITC for 2 days at 24 degrees C; plating on SSDC agar (2 days at 30 degrees C). (2) Pre-enrichment in TSB for 1 day at 24 degrees C; enrichment in BOS for 5 days at 24 degrees C; alkali treatment (mixing 0.5 ml enriched broth with 4.5 ml of 0.5% KOH in 0.5% NaCl for 5 s); plating on CIN agar (2 days at 24 degrees C).

Culture Media↗
PubMed1991

Cloning of the nitrate-nitrite reductase gene cluster of Penicillium chrysogenum and use of the niaD gene as a homologous selection marker.

A new homologous transformation system for the filamentous fungus Penicillium chrysogenum is described. The system is based on complementation of niaD mutants using the nitrate reductase structural gene (niaD) of P. chrysogenum. Spontaneous niaD mutants were identified after selection for chlorate resistance, in growth tests and subsequent complementation with the niaD gene of Aspergillus oryzae. The P. chrysogenum niaD gene was isolated from a genomic library using the Aspergillus nidulans niaD gene as a probe. After subcloning of the hybridizing fragment, the vector obtained, pPC1-1, was capable of transforming a P. chrysogenum niaD mutant at an average of 40 transformants per micrograms of circular DNA. Southern analysis of genomic DNA from a number of transformants showed that pPC1-1 DNA was integrated predominantly at sites other than the niaD locus. Using hybridization analysis it was shown that the niaD gene of P. chrysogenum is clustered with the nitrite reductase gene (niiA). From analysis of the nucleotide sequences of parts of the niaD and niiA genes of P. chrysogenum and comparison of these sequences with nucleotide sequences of the corresponding A. nidulans genes it was deduced that the P. chrysogenum genes are divergently transcribed.

Cloning, Molecular↗
PubMed1990

Chlorine dioxide and hemodialysis.

In the United States chlorination of potable water supplies has been the standard method of disinfection for about 75 years. In recent times concern has been raised about the propensity of chlorination to introduce potentially carcinogenic trihalomethanes (THM) such as chloroform into finished water. The levels of THM introduced depend on many factors including the quality of the raw water. Numerous community water treatment facilities are experiencing difficulty in meeting current U.S. Environmental Protection Agency standards, and it is likely that the permissible levels may be lowered in the future. An alternative to chlorination which does not generate THM during disinfection is chlorine dioxide, but there are concerns about the acute and chronic toxicity of ClO2 and its disinfection by-products, chlorite and chlorate. Deleterious effects of moderately high levels of these oxychlorines have been demonstrated experimentally on red blood cells, thyroid function, and development in laboratory animals. Adverse effects in controlled prospective studies in humans and in actual use situations in community water supplies have as yet failed to reveal clear evidence of adverse health effects. Among groups who may be at special risk from this suggested alternative are patients who must undergo chronic extracorporeal hemodialysis. The special needs, precautions, and experience to date in regard to finished water are reviewed. Again, very limited human experience has failed to reveal adverse health effects. Further study, caution, and extreme vigilance are indicated, but dialysis patients in carefully controlled facilities may be at no greater risk than the general population.

Animals↗
PubMed1982

The ionic selectivity of two voltage activated channels and an acetylcholine activated channel in an Onchidium neuron.

1. The selectivities of the ion channels underlying the action potential and the hyperpolarizing response to acetylcholine of the GH cell of Onchidium have been analysed. 2. The rising phase of the action potential is due to an increase in the permeability of the membrane to both Na+ and Ca2+. The Na+ channel is permeable to Li+ and is somewhat permeable to formamidinium, guanidinium and ammonium ions. The Ca2+ channel is permeable to Sr2+ and Ba2+, but not to Mn2+ and Mg2+. 3. The Cl- channel operated by ACh is permeable to chlorate, but not to formate and propionate ions. 4. The selectivities of these channels are similar to those of a number of other channels in other organisms.

Acetylcholine↗
PubMed1990

Molybdenum cofactor negative mutants of Escherichia coli use citrate anaerobically.

Anaerobically, Escherichia coli cannot grow using either glycerol or citrate as sole carbon and energy source. However, it has been reported that a mixture of glycerol and citrate will support growth. We have found that wild-type strains of E. coli K-12 do not grow on glycerol plus citrate anaerobically. However, growth eventually occurs due to the frequent appearance of mutants. We found that such Cit+ mutants were defective in anaerobic respiration with nitrate or trimethylamine-N-oxide and were chlorate resistant (i.e. molybdenum cofactor deficient). Conversely, well characterized mutants in any of chlA, B, D, E, G and N were also able to use citrate anaerobically. No anaerobic growth differences between wild type and chl mutants were observed either with fermentable sugars or with glycerol plus fumarate or glycerol plus tartrate. Citrate lyase was induced anaerobically by citrate and repressed by glucose in both wild type strains and chl mutants. Furthermore, levels of citrate lyase, fumarate reductase, malate dehydrogenase, fumarase and alcohol dehydrogenase were similar in both types of strains under anaerobic conditions. It is conceivable that a functioning molybdenum cofactor prevents use of citrate by keeping citrate lyase in the inactive form.

Aconitate Hydratase↗
PubMed1991

Mutagenesis of the cyanobacterium Spirulina platensis by UV and nitrosoguanidine treatment.

The production of Spirulina platensis cells resistant to 8-azaguanine or beta-(2-thienyl)-DL-alanine following mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and UV-irradiation is described. The conditions for the mutagenesis were determined by monitoring cell viability and the appearance of the two types of mutants as a function of the stage of growth of the tricomes and the length and the conditions of the treatment. The optimal conditions for UV and MNNG mutagenesis were found to be 1-3 min irradiation and 30 min incubation with 50 micrograms MNNG/ml of tricomes derived from cultures entering stationary phase sonicated for 10 s and 5 s respectively. Under these conditions beta-(2-thienyl)-DL-alanine-resistant mutants appeared at a frequency greater than or equal to 10(-4) and greater than or equal to 10(-5) following UV- and MNNG-mutagenesis, respectively. Mutants resistant to 8-azaguanine were found at a frequency approx. 10(-5) only after MNNG mutagenesis. A few chlorate-resistant mutants were also obtained following UV treatment.

Cyanobacteria↗
PubMed1989

Cloning of the nitrate reductase gene (niaD) of Aspergillus nidulans and its use for transformation of Fusarium oxysporum.

An heterologous transformation system for the phytopathogenic fungus Fusarium oxysporum has been developed based on the use of the Aspergillus nidulans nitrate reductase gene (niaD). F. oxysporum nia- mutants were easily selected by chlorate resistance. The A. nidulans niaD gene was isolated from a gene library by complementation of an A. nidulans niaD mutant. The cloned gene is capable of transforming F. oxysporum nia- mutants at a frequency of up to ten transformants per microgram of DNA. Southern analysis of the DNA of the F. oxysporum transformants showed that transformation resulted in integration of one or more copies of the vector DNA into the genome.

Aspergillus nidulans↗