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PubMed2001

Cellular compartmentation of ammonium assimilation in rice and barley.

This review describes immunolocalization studies of the tissue and cellular location of glutamine synthetase (GS; EC 6.3.1.2) and glutamate synthase (Fd GOGAT; EC 1.4.7.1 and NADH-GOGAT; EC 1.4.1.14) proteins in roots and leaves of rice (Oryza sativa L.) and barley (Hordeum vulgare L.). In rice, cytosolic GS (GS1) protein was distributed homogeneously through all cells of the root. NADH GOGAT protein was strongly induced and its cellular location altered by ammonium treatment, becoming concentrated within the epidermal and exodermal cells. Fd GOGAT protein location changed with root development, from a widespread distribution in young cells to becoming concentrated within the central cylinder as cells matured. Plastid GS protein was barely detectable in rice roots, but was the major isoform in leaves, being present in the mesophyll and parenchyma sheath cells. GS1 was specific to the vascular bundle, as was NADH GOGAT, whereas Fd GOGAT was primarily found in mesophyll cells. In barley roots, GS1 protein was found in the cortical and vascular parenchyma and its concentration was highest in N-deficient seedlings. Plastid GS protein was detected in both cortical and vascular cells, where different plastid forms, containing different concentrations of GS protein, were identified. In barley leaves, GS2 protein was detected in the mesophyll chloroplasts and GS1 was found in the mesophyll and vascular cells. N nutrition strongly influenced this distribution, with a marked increase in GS1 concentration in the vascular cells in response to nitrate and ammonium, and an increase in mesophyll GS2 concentration in nitrate-grown seedlings. Fd GOGAT protein was found in both the mesophyll and vascular plastids. These localization studies show that the GS/GOGAT cycle is highly compartmentalized at both the subcellular and cellular levels. Reasons for this compartmentation, and the roles of each isoform, are discussed.

Cell Compartmentation↗
PubMedDate not supplied

[Methionine sulfoximine and phosphinothricin--glutamine synthetase inhibitors and activators and their herbicidal activity (A review)].

Derivatives of methionine sulfoximine (MSO) and phosphinothrycin (PPT), which are analogues of glutamate, exhibit selective herbicidal activity. This effect is accounted for by impairments of nitrogen metabolism, resulting from inhibition of its key enzyme in plants, glutamine synthetase (EC 6.3.1.2). Inhibition of the enzyme causes ammoniac nitrogen to accumulate and terminates the synthesis of glutamine. Changes in the content of these two metabolites (excess ammonium and glutamine deficiency) act in a concert to cause plant death. However, low concentrations of MSO, PPT, and their metabolites produce an opposite effect: glutamine synthetase is activated, with concomitant stimulation of plant growth and productivity. The mechanisms whereby MSO and PPT affect glutamine synthetase activity are discussed in the context of nitrogen metabolism in plants.

Aminobutyrates↗
PubMed2004

Statistical model for assessing the portion of fine particulate matter transported regionally and long range to urban air.

OBJECTIVES: This study attempted to develop a simple statistical model for assessing the contribution of aerosols transported regionally and those transported long range to the concentrations of fine particulate matter (PM2.5) in urban air in Helsinki. METHODS: The construction and testing of the linear regression model was based on PM2.5 measurement data from two locations in the City of Helsinki (Vallila & Kallio) and on ion concentration data obtained from the three nearest monitoring stations of The Co-operative Programme for Monitoring and Evaluating of the Long-range Transmission of Air Pollutants in Europe (EMEP). The "ion sum" was calculated on the basis of the following daily measured EMEP parameters in 1998--2000: (i) sulfate (SO4(2-)), (ii) the sum of nitrate (NO3-) and nitrogen acid (HNO3), and (iii) the sum of ammonium (NH4+) and ammonia (NH3). The ion sum was compared with sulfate as the proxy variable for PM2.5 transported long range. RESULTS: The correlation of the daily average PM2.5 concentration with the ion sum (R2=0.59-0.61) was higher than that with sulfate (R2 = 0.48-0.50). The regression estimates showed relatively small year-to-year variation. The contribution of long-range transport to the measured PM2.5 concentration in urban air in Helsinki was estimated to be 64-76%. CONCLUSIONS: The results showed a strong association between the ion sum interpolated from the EMEP data and the PM2.5 concentration measured at urban sites in Helsinki. This association can be utilized in local dispersion modeling of the PM2.5 concentration in urban air.

Air Pollutants↗
PubMed1980

[Effects of experimental hyperammonemia on the secretion of insulin and glucagon in the rat].

In order to investigate the controverted effect of ammonia on insulin and glucagon secretion 3 groups of 55 rats were perfused either by Na+ acetate (controls), either by NH4+ acetate: in the first group plasma insulin (IRI) and glucagon (IRG) levels were compared before and after perfusion; the second group was supplemented by glucose perfusion (1 g/100 g/hour); in the last group an arginine perfusion (1 g/kg/min) was started 15 min after the beginning of NH4+ or Na acetate and IRI and IRG levels were determined in the portal blood. Hyperammonemia, which reached about 500 microgram/dl, reduced significantly the IRI portal level and the IRI secretion induced by glucose or arginine, whereas basal or stimulated IRG levels are not modified. The ratio IRI:IRG is diminished in each group perfused with NH4+ acetate. Our results show that ammonia inhibits insulin without modifications in the glucagon secretion; hyperglucagonemia and hyperinsulinism reported in hepatic encephalopathy with chronic hyperammonemia may not be attributed to an effect of ammonia.

Ammonia↗
PubMed1997

Morphological differentiation and nitrogen fixation in transposon generated mutants of Anabaena 7120.

Mutants having partially repressed glutamine sythetase (transferase) activity and high nitrogenase activity were isolated following transposon mutagenesis. Two of these mutants M11 and M73 showed a decrease in heterocyst frequency compared with the wild type strain. The level of the enzyme nitrogenase was much higher in all the mutant strains. Nitrate and ammonia completely suppressed heterocyst differentiation and nitrogenase activity in mutants M11 and M73, but mutant M55 differentiated heterocysts and showed nitrogenase activity even in the presence of these combined inorganic nitrogen sources. Heterocyst frequency in the M55 mutant was much more than that of the wild strain. Glutamine as a nitrogen source completely suppressed differentiation of heterocysts as well as nitrogenase activity, irrespective of the presence or absence of the glutamate analogue MSX which relieved the inhibitory effect of nitrate or ammonia on heterocyst differentiation and nitrogenase activity. The level of the intracellular ammonium pool was maximal in the wild strain in all the nitrogen sources used for growth. Cultures raised with ammonium chloride gave maximum values for intracellular ammonium pool in all the mutant strains and the wild strain. Mutants showed about 55 to 60% less GS (transferase) activity than the wild strain.

Anabaena↗
PubMed2001

Mixture of N-carbamoyl-L-glutamate plus L-arginine can protect rats with liver cirrhosis from acute ammonia intoxication.

BACKGROUND/AIMS: We earlier reported that N-carbamoyl-L-glutamate (CG) plus L-arginine (Arg) protected normal and 70% hepatectomized rats from intoxication by a lethal or sub-lethal dose of ammonium acetate, respectively. In the present study, the protective effect of these compounds on cirrhotic rats was assessed. METHODS: CG plus Arg were administered prior to the injection of a sub-lethal dose of ammonium acetate into dimethylnitrosamine-induced cirrhotic rats. Control rats were given phosphate-buffered saline (PBS) instead of the mixture. The behavior of the rats was monitored until the time of sacrifice. Blood ammonia level, blood urea nitrogen (BUN) and liver carbamoylphosphate synthetase I (CPS I) activity were determined. RESULTS: Pretreatment of rats with the mixture of CG plus Arg could significantly lower the blood ammonia level (P<0.05), increase the activity of CPS I (P<0.05), improve abnormal behavior associated with ammonia intoxication (P<0.05), and increase BUN (P<0.05), as compared with the PBS-injected control group. There were significantly close correlations between (1) the increase of CPS I activity; (2) the improvement of abnormal behavior; (3) the increase of BUN; and (4) the decrease of the blood ammonia level. CONCLUSIONS: A mixture of CG plus Arg could protect rats with liver cirrhosis from acute ammonia intoxication.

Acetates↗
PubMed2004

First characterization of the ammine-ammonium complex [(NH4(NH3)4)2(mu-NH3)2]2+ in the crystal structure of [NH4(NH3)4][B(C6H5)4].NH3 and the [NH4(NH3)4]+ complex in [NH4(NH3)4][Ca(NH3)7]As3S6.2NH3 and [NH4(NH3)4][Ba(NH3)8]As3S6.NH3.

The compound [NH4(NH3)4][B(C6H5)4].NH3 (1) was prepared by the reaction of NaB(C(6)H(5))(4) with a proton-charged ion-exchange resin in liquid ammonia. [NH(4)(NH(3))(4)][Ca(NH(3))(7)]As(3)S(6).2NH(3) (2) and [NH4(NH3)4][Ba(NH3)8]As3S6.NH3 (3) were synthesized by reduction of As(4)S(4) with Ca and Ba in liquid ammonia. All ammoniates were characterized by low-temperature single-crystal X-ray structure analysis. They were found to contain the ammine-ammonium complex with the maximal possible number of coordinating ammonia molecules, the [NH4(NH3)4]+ ion. 1 contains a special dimer, the [(NH4(NH3)4)2(mu-NH3)2]2+ ion, which is formed by two[NH4(NH3)4]+ ions linked by two ammonia molecules. The H(3)N-H...N hydrogen bonds in all three compounds range from 1.82 to 2.20 A (DHA = Donor-H... Acceptor angles: 156-178 degrees). In 2 and 3, additional H(2)N-H...S bonds to the thioanions are observed, ranging between 2.49 and 3.00 A (DHA angles: 120-175 degrees). Two parallel phenyl rings of the [B(C(6)H(5))(4)](-) anion in 1 form a pi...pi hydrogen bond (C...C distance, 3.38 A; DHA angles, 82 degrees), leading to a dimeric [B(C6H5)4]2(2-) ion.

Journal Article↗
PubMed1992

A monoamine-regulated Klebsiella aerogenes operon containing the monoamine oxidase structural gene (maoA) and the maoC gene.

The Klebsiella aerogenes gene maoA, which is involved in the synthesis of monoamine oxidase, was induced by tyramine and the related compounds, subjected to catabolite and ammonium ion repression, and cloned. The nucleotide sequence of the region involved in monoamine oxidase synthesis was determined. Two open reading frames, the maoA gene and a hitherto unknown gene (maoC), were found. These are located between a potential promoter sequence and a transcriptional terminator sequence. A region of the Escherichia coli chromosome that was highly homologous to the Klebsiella maoA gene was found. The potential maoA gene is located at 30.9 min on the E. coli chromosome. Analysis of the amino acid sequences of the first 11 amino acids from the N terminus of the purified monoamine oxidase agrees with those deduced from the nucleotide sequence of the maoA gene. The leader peptide extends over 30 amino acids and has the characteristics of a signal sequence. Primer extension and S1 nuclease mapping of transcripts generated in vivo suggests that the tyramine-induced mRNA starts at a site 62 bases upstream from the ATG initiation codon of the maoC gene. In the putative promoter region, a high degree of similarity to the consensus sequence for the binding site of cyclic AMP receptor protein was found. Thus, the mao region is composed of two cistrons, and the mao operon is regulated by monoamine compounds, glucose, and ammonium ions.

Amino Acid Sequence↗
PubMed1951

Relative concentrations of N15 in urinary ammonia N and urea N after feeding N15-labeled compounds.

Available data on the isotopic ratio See PDF for Equation of ammonia (r(a)) and that of urea (r(u)) after a single feeding of glycine, aspartic acid, and ammonium citrate are analyzed. From this analysis the following conclusions are drawn. 1. The isotopic ratio See PDF for Equation of ammonia (r(a)) is always higher than that of urea (r(u)) in the initial period after a single feeding of isotopic glycine or aspartic acid, but the relation is reversed later. A similar relation probably holds after feeding isotopic ammonia. 2. It is pointed out that the ratio of average r(a) to average r(u) depends on the time interval for which urine is collected, on the schedule of feeding, and probably also on the amount taken at each feeding. When the amount fed and the feeding schedule are unknown, theoretical interpretation of the ratio of average r(u) to average r(u) is impossible. 3. At the point of maximum isotopic ratio of urea, it is very probably equal to the isotopic ratio of ammonia. A possible explanation is suggested.

Ammonia↗
PubMed1993

The internal quaternary ammonium receptor site of Shaker potassium channels.

Quaternary ammonium (QA) compounds inhibit K+ conductance by entering and occluding the open pore of voltage-activated K+ channels. We characterized the effects of a series of alkyl-triethylammonium blockers on the Shaker K+ channel and tested them on a series of site-directed mutants of the channel protein in order to define the structural features of the binding sites. We found that mutations in two regions of the channel protein, the pore (P) region and the last transmembrane sequence (S6), appear to alter QA binding, not through their effects on gating but perhaps through direct effects on the binding site. Several mutations in the P region affect tetraethylammonium binding but have minimal effects on longer blockers, suggesting that the hydrophobic tail contributes to binding in a nonadditive fashion. Binding of the longer blockers can be affected by varying the hydrophobicity of 1 residue within S6 by site-specific substitution, in a manner consistent with a direct hydrophobic interaction between the side chain at this site and the alkyl chains of the blocker.

Amino Acid Sequence↗
PubMed2001

Insecticidal activity of glufosinate through glutamine depletion in a caterpillar.

The herbicide glufosinate-ammonium (GLA) is a competitive inhibitor of glutamine synthetase (GS), an enzyme converting glutamate to glutamine in both plants and animals. Because GS is essential for ammonia detoxification in plants, GLA treatment disrupts photorespiration by causing a build-up of ammonia and a loss of glutamine in plant tissues. This study reports that GLA applied to leaf surfaces is also toxic to 5th-instar caterpillars of the skipper butterfly Calpodes ethlius (LD50 = 400 mg kg-1). After ingesting GLA, caterpillars stopped feeding and became dehydrated through a loss of rectal function. Caterpillars showed symptoms of neurotoxicity, such as proleg tremors, body convulsions and complete paralysis before death. Incubation of several tissues isolated from normal feeding-stage caterpillars with the GS substrates glutamate and ammonium showed that GLA inhibited GS activity in vitro. Within 24 h of ingesting GLA, caterpillars had a greatly reduced glutamine content and the ammonium ion levels had more than doubled. Injection of ammonium chloride into non-GLA-treated caterpillars had no deleterious effect, suggesting that glutamine depletion, and not a rise in body ammonium, was the primary cause of GLA toxicity following GS inhibition. This was supported by the observation that the onset of the symptoms of GLA poisoning could be postponed by giving GLA-fed caterpillars several subsequent daily injections of glutamine. The effective GLA dose fed to 5th-instar caterpillars in this study was comparable to the amount that might realistically by acquired from feeding on GLA-treated crops.

Amino Acids↗