Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.2 (nitrate reductase)
 3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Fructose 2,6-bisphosphate (fru-2,6-P2) is a signalling metabolite that regulates photosynthetic carbon partitioning in plants. The content of fru-2,6-P2 in Arabidopsis leaves varied in response to photosynthetic activity with an abrupt decrease at the start of the photoperiod, gradual increase through the day, and modest decrease at the start of the dark period. In Arabidopsis suspension cells, fru-2,6-P2 content increased in response to an unknown signal upon transfer to fresh culture medium. This increase was blocked by either 2-deoxyglucose or the protein phosphatase inhibitor, calyculin A, and the effects of calyculin A were counteracted by the general protein kinase inhibitor K252a. The changes in fru-2,6-P2 at the start of dark period in leaves and in the cell experiments generally paralleled changes in nitrate reductase (NR) activity. NR is inhibited by protein phosphorylation and binding to 14-3-3 proteins, raising the question of whether fructose-6-phosphate,2-kinase/fructose-2,6-bisphosphatase protein from Arabidopsis thaliana (AtF2KP), which both generates and hydrolyses fru-2,6-P2, is also regulated by phosphorylation and 14-3-3s. Consistent with this hypothesis, AtF2KP and NR from Arabidopsis cell extracts bound to a 14-3-3 column, and were eluted specifically by a synthetic 14-3-3-binding phosphopeptide (ARAApSAPA). 14-3-3s co-precipitated with recombinant glutathione S-transferase (GST)-AtF2KP that had been incubated with Arabidopsis cell extracts in the presence of Mg-ATP. 14-3-3s bound directly to GST-AtF2KP that had been phosphorylated on Ser220 (SLSASGpSFR) and Ser303 (RLVKSLpSASSF) by recombinant Arabidopsis calcium-dependent protein kinase isoform 3 (CPK3), or on Ser303 by rat liver mammalian AMP-activated protein kinase (AMPK; homologue of plant SNF-1 related protein kinases (SnRKs)) or an Arabidopsis cell extract. We have failed to find any direct effect of 14-3-3s on the F2KP activity in vitro to date. Nevertheless, our findings indicate the possibility that 14-3-3 binding to SnRK1-phosphorylated sites on NR and F2KP may regulate both nitrate assimilation and sucrose/starch partitioning in leaves.
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PMID:Phosphorylation and 14-3-3 binding of Arabidopsis 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. 1487 7

In the growing chloronema cell suspension cultures of the moss Funaria hygrometrica Hedw., activities of several enzymes have been found to be cell-density-dependent. Cyclic nucleotide phosphodiesterase (cNPDE), nitrate reductase (NR), and protein kinase showed highest activity at a low cell density (1 to 2 milligrams per milliliter) while indoleacetic acid (IAA) oxidase and peroxidase were highest at a high cell density (>10 milligrams per milliliter). 3'-Nucleotidase and the glycolytic enzymes (aldolase, hexokinase, phosphofructokinase, phosphoglucoisomerase, pyruvate kinase, and triose phosphate isomerase) showed no significant dependence on the cell density. Alternatively, if the NR and peroxidase activities were determined as a function of time in batch cultures, their levels were maximal 60 to 70 and 320 hours after subculture, respectively, the corresponding cell densities being 1 to 2 and 23 milligrams per milliliter. The relationship between cell density and NR and peroxidase activities is the same, whether these enzymes are measured in batch cultures during a growth cycle or in the cells cultured at different initial inoculum densities for a constant time. Conventionally enzymic changes have been correlated with growth phases; however, it is felt that the pattern of enzymic activities can also be interpreted as cell-density-dependent.In moss protonema, the dependence of cNPDE, IAA oxidase, and peroxidase on cell density may play an important role in modulating the endogenous levels of IAA and cAMP, both of which regulate the differentiation of specific cell types (Johri and Desai 1973 Nature New Biol 245: 223-224; and Handa and Johri 1976 Nature 259: 480-482).
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PMID:Cell-density-dependent Changes in the Metabolism of Chloronema Cell Cultures: I. Relationship between Cell Density and Enzymic Activities. 1666 Sep 5

Trehalose-6-phosphate is a 'sugar signal' that regulates plant metabolism and development. The Arabidopsis genome encodes trehalose-6-phosphate synthase (TPS) and trehalose-6-phosphatase (TPP) enzymes. It also encodes class II proteins (TPS isoforms 5-11) that contain both TPS-like and TPP-like domains, although whether these have enzymatic activity is unknown. In this paper, we show that TPS5, 6 and 7 are phosphoproteins that bind to 14-3-3 proteins, by using 14-3-3 affinity chromatography, 14-3-3 overlay assays, and by co-immunoprecipitating TPS5 and 14-3-3 isoforms from cell extracts. GST-TPS5 bound to 14-3-3s after in vitro phosphorylation at Ser22 and Thr49 by either mammalian AMP-activated protein kinase (AMPK) or partially purified plant Snf1-related protein kinase 1 (SnRK1s). Dephosphorylation of TPS5, or mutation of either Ser22 or Thr49, abolished binding to 14-3-3s. Ser22 and Thr49 are both conserved in TPS5, 7, 9 and 10. When GST-TPS5 was expressed in human HEK293 cells, Thr49 was phosphorylated in response to 2-deoxyglucose or phenformin, stimuli that activate the AMPK via the upstream kinase LKB1. 2-deoxyglucose stimulated Thr49 phosphorylation of endogenous TPS5 in Arabidopsis cells, whereas phenformin did not. Moreover, extractable SnRK1 activity was increased in Arabidopsis cells in response to 2-deoxyglucose. The plant kinase was inactivated by dephosphorylation and reactivated by phosphorylation with human LKB1, indicating that elements of the SnRK1/AMPK pathway are conserved in Arabidopsis and human cells. We hypothesize that coordinated phosphorylation and 14-3-3 binding of nitrate reductase (NR), 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (F2KP) and class II TPS isoforms mediate responses to signals that activate SnRK1.
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PMID:Phosphorylation and 14-3-3 binding of Arabidopsis trehalose-phosphate synthase 5 in response to 2-deoxyglucose. 1677 75

The relationship between nitric oxide (NO) and salicylic acid (SA) was investigated in Arabidopsis thaliana. Here it is shown that SA is able to induce NO synthesis in a dose-dependent manner in Arabidopsis. NO production was detected by confocal microscopic analysis and spectrofluorometric assay in plant roots and cultured cells. To identify the metabolic pathways involved in SA-induced NO synthesis, genetic and pharmacological approaches were adopted. The analysis of the nia1,nia2 mutant showed that nitrate reductase activity was not required for SA-induced NO production. Experiments performed in the presence of a nitric oxide synthase (NOS) inhibitor suggested the involvement of NOS-like enzyme activity in this metabolic pathway. Moreover, the production of NO by SA treatment of Atnos1 mutant plants was strongly reduced compared with wild-type plants. Components of the SA signalling pathway giving rise to NO production were identified, and both calcium and casein kinase 2 (CK2) were demonstrated to be involved. Taken together, these results suggest that SA induces NO production at least in part through the activity of a NOS-like enzyme and that calcium and CK2 activity are essential components of the signalling cascade.
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PMID:Salicylic acid activates nitric oxide synthesis in Arabidopsis. 1731 74

The yeast regulatory protein kinase, general control non-derepressible-2 (GCN2) plays a key role in general amino acid control. GCN2 phosphorylates the alpha subunit of the trimeric eukaryotic translation initiation factor-2 (eIF2), bringing about a decrease in the general rate of protein synthesis but an increase in the synthesis of GCN4, a transcription factor that promotes the expression of genes encoding enzymes for amino acid biosynthesis. The present study concerned the phosphorylation of Arabidopsis eIF2alpha (AteIF2alpha) by the Arabidopsis homologue of GCN2, AtGCN2, and the role of AtGCN2 in regulating genes encoding enzymes of amino acid biosynthesis and responding to virus infection. A null mutant for AtGCN2 called GT8359 was obtained and western analysis confirmed that it lacked AtGCN2 protein. GT8359 was more sensitive than wild-type Arabidopsis to herbicides that affect amino acid biosynthesis. Phosphorylation of AteIF2alpha occurred in response to herbicide treatment but only in wild-type Arabidopsis, not GT8359, showing it to be AtGCN2-dependent. Expression analysis of genes encoding key enzymes for amino acid biosynthesis and nitrate assimilation revealed little effect of loss of AtGCN2 function in GT8359 except that expression of a nitrate reductase gene, NIA1, was decreased. Analysis of wild-type and GT8359 plants infected with Turnip yellow mosaic virus or Turnip crinkle virus showed that AteIF2alpha was not phosphorylated.
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PMID:GCN2-dependent phosphorylation of eukaryotic translation initiation factor-2alpha in Arabidopsis. 1860 15

In higher plants, light is crucial for regulation of nitrate uptake, translocation and assimilation into organic compounds. Part of this metabolism is tightly coupled to photosynthesis because the enzymes involved, nitrite reductase and glutamate synthase, are localized to the chloroplasts and receive reducing power from photosynthetic electron transport. However, important enzymes in nitrate acquisition and reduction are localized to cellular compartments other than chloroplasts and are also up-regulated by light, i.e. transporters in cell and organellar membranes and nitrate reductase in the cytosol. This review describes the different light-dependent signalling cascades regulating nitrate metabolism at the transcriptional as well as post-transcriptional level, and how reactions in different compartments of the cell are co-ordinated. Essential players in this network are phytochrome and HY5 (long hypocotyls 5)/HYH (HY5 homologue)-dependent signalling pathways, the energy-related AMPK (AMP-activated protein kinase) protein kinase homologue SNRK1 (sucrose non-fermenting kinase 1-related kinase), chloroplastic thioredoxins and the prokaryotically originated PII protein. A complex light-dependent network of regulation emerges, which appears to be necessary for optimal nitrogen assimilation and for avoiding the accumulation of toxic intermediates and side products, such as nitrite and reactive oxygen compounds.
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PMID:Signalling cascades integrating light-enhanced nitrate metabolism. 1877 47

The proteins kinases SNF1/AMPK/SnRK1 are a subfamily of serine/threonine kinases that act as metabolite sensors to constantly adapt metabolism to the supply of, and demand for, energy. In the yeast Saccharomyces cerevisiae, the SNF1 complex is a central component of the regulatory response to glucose starvation. AMP activated protein kinase (AMPK) the mammalian homologue of SNF1, plays a central role in the regulation of energy homeostasis at the cellular as well as the whole-body levels. In Arabidopsis thaliana, SnRK1.1 and SnRK1.2 have recently been described as central integrators of a transcription network for stress and energy signalling. In this study, biochemical analysis established SnRK1.1 as the major SnRK1 isoform both in isolated cells and leaves. In order to elucidate the function of SnRK1.1 in Arabidopsis thaliana, transgenic plants over-expressing SnRK1.1 were produced. Genetic, biochemical, physiological and molecular analyses of these plants revealed that SnRK1.1 is implicated in sugar and ABA signalling pathways. Modifications of the starch and soluble sugar content were observed in the 35S:SnRK1.1 transgenic lines. Our studies also revealed modifications of the activity of essential enzymes such as nitrate reductase or ADP-glucose pyrophosphorylase, and of the expression of several sugar-regulated genes, confirming the central role of the protein kinase SnRK1 in the regulation of metabolism.
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PMID:SnRK1 (SNF1-related kinase 1) has a central role in sugar and ABA signalling in Arabidopsis thaliana. 1930 19

The mechanisms involved in sensing oxidative signalling molecules, such as H2O2, in plant and animal cells are not completely understood. In the present study, we tested the postulate that oxidation of Met (methionine) to MetSO (Met sulfoxide) can couple oxidative signals to changes in protein phosphorylation. We demonstrate that when a Met residue functions as a hydrophobic recognition element within a phosphorylation motif, its oxidation can strongly inhibit peptide phosphorylation in vitro. This is shown to occur with recombinant soybean CDPKs (calcium-dependent protein kinases) and human AMPK (AMP-dependent protein kinase). To determine whether this effect may occur in vivo, we monitored the phosphorylation status of Arabidopsis leaf NR (nitrate reductase) on Ser534 using modification-specific antibodies. NR was a candidate protein for this mechanism because Met538, located at the P+4 position, serves as a hydrophobic recognition element for phosphorylation of Ser534 and its oxidation substantially inhibits phosphorylation of Ser534 in vitro. Two lines of evidence suggest that Met oxidation may inhibit phosphorylation of NR-Ser534 in vivo. First, phosphorylation of NR at the Ser534 site was sensitive to exogenous H2O2 and secondly, phosphorylation in normal darkened leaves was increased by overexpression of the cytosolic MetSO-repair enzyme PMSRA3 (peptide MetSO reductase A3). These results are consistent with the notion that oxidation of surface-exposed Met residues in kinase substrate proteins, such as NR, can inhibit the phosphorylation of nearby sites and thereby couple oxidative signals to changes in protein phosphorylation.
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PMID:Coupling oxidative signals to protein phosphorylation via methionine oxidation in Arabidopsis. 1966 8

In response to biotic and abiotic stresses, plants induce a complex array of pathways and protein phosphorylation cascades which generally lead to a response aimed at mitigating the particular insult. In many cases, H2O2 has been implicated as the signalling molecule, but, although progress has been made in assembling the downstream components of these signalling pathways, far less is known about the mechanism by which the signal is perceived. In this issue of the Biochemical Journal, Hardin et al. provide evidence for a plausible mechanism by which plants perceive H2O2. Evidence is presented for chemical oxidation of methionine residues by H2O2 at critical hydrophobic positions within the canonical motifs that define the phosphorylation sites of a number of enzymes, thus inhibiting binding of protein kinases. This process is reversible by MSR (methionine sulfoxide reductase) activity in vivo. Using synthetic peptides for a number of enzymes which are phosphorylated by families of protein kinases, including the CDPK (calcium-dependent protein kinase) and AMPK (AMP-activated protein kinase) families, coupled with in vivo studies of assimilatory plant nitrate reductase, the authors demonstrate that this mechanism regulates the ability of kinases to bind the target protein, directly linking oxidative signals to changes in protein phosphorylation. These results may have widespread implications for the perception of redox signalling in plants and animals.
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PMID:Oxidation of methionine residues: the missing link between stress and signalling responses in plants. 1952 23

SUMMARY A non-pathogenic mutant of Colletotrichum acutatum, designated Ca5, exhibited epiphytic hyphal growth and did not cause lesions on strawberry plants but grew necrotrophically when inoculated directly onto wounded stolons. In the absence of an external nitrogen source, the mutant exhibited extended germ-tube growth prior to appressorium formation. The deduced product of the impaired gene (nir1) is similar to NirA, an Aspergillus nidulans transcriptional regulator of nitrogen metabolism. Inoculation of leaves with wild-type or Ca5 conidia in the presence of a preferred nitrogen source resulted in massive epiphytic hyphal production, appressorium formation and rapid symptom development. Expression of C. acutatum wild-type nitrate reductase (nit1) and glutamine synthetase (gln1) was induced by nitrate but only nit1 expression was repressed in a rich medium. nit1 transcription increased during the appressorium-production stage, indicating that nitrogen starvation constitutes a cue for the regulation of appressorium development. The presence of nit1 transcript during various phases of infection is indicative of partial nitrogen starvation in planta. cAMP-dependent protein kinase A (PKA) was determined to be a negative regulator of immediate post-germination appressoria formation in the wild-type. As inhibition of PKA activity in the nir1 mutant did not affect appressoria formation, we suggest that NIR1 acts either in parallel or downstream of the PKA pathway. Our results show that nir1 is a pathogenicity determinant and a regulator of pre-infection development under nitrogen-starvation conditions and that nitrogen availability is a significant factor in the pre-penetration phase.
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PMID:A defect in nir1, a nirA-like transcription factor, confers morphological abnormalities and loss of pathogenicity in Colletotrichum acutatum. 2050 51


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