Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:1.7.1.2 (nitrate reductase)
3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nitrate is a significant nitrogen source for plants and microorganisms. Recent molecular genetic analyses of representative bacterial species have revealed structural and regulatory genes responsible for the nitrate-assimilation phenotype. Together with results from physiological and biochemical studies, this information has unveiled fundamental aspects of bacterial nitrate assimilation and provides the foundation for further investigations. Well-studied genera are: the cyanobacteria, including the unicellular Synechococcus and the filamentous Anabaena; the gamma-proteobacteria Klebsiella and Azotobacter; and a Gram-positive bacterium, Bacillus. Nitrate uptake in most of these groups seems to involve a periplasmic binding protein-dependent system that presumably is energized by ATP hydrolysis (ATP-binding cassette transporters). However, Bacillus may, like fungi and plants, utilize electrogenic uptake through a representative of the major facilitator superfamily of transport proteins. Nitrate reductase contains both molybdenum cofactor and an iron-sulfur cluster. Electron donors for the enzymes from cyanobacteria and Azotobacter are ferredoxin and flavodoxin, respectively, whereas the Klebsiella and Bacillus enzymes apparently accept electrons from a specific NAD(P)H-reducing subunit. These subunits share sequence similarity with the reductase components of bacterial aromatic ring-hydroxylating dehydrogenases such as toluene dioxygenase. Nitrite reductase contains sirohaem and an iron-sulfur cluster. The enzymes from cyanobacteria and plants use ferredoxin as the electron donor, whereas the larger enzymes from other bacteria and fungi contain FAD and NAD(P)H binding sites. Nevertheless, the two forms of nitrite reductase share recognizable sequence and structural similarity. Synthesis of nitrate assimilation enzymes and uptake systems is controlled by nitrogen limitation in all bacteria examined, but the relevant regulatory proteins exhibit considerable structural and mechanistic diversity in different bacterial groups. A second level of control, pathway-specific induction by nitrate and nitrite in Klebsiella, involves transcription antitermination. Several issues await further experimentation, including the mechanism and energetics of nitrate uptake, the pathway(s) for nitrite uptake, the nature of electron flow during nitrate reduction, and the action of transcriptional regulatory circuits. Fundamental knowledge of nitrate assimilation physiology should also enhance the study of nitrate metabolism in soil, water and other natural environments, a challenging topic of considerable interest and importance.
...
PMID:Nitrate assimilation by bacteria. 932 45

In Synechococcus sp. strain PCC 7942, an ATP-binding cassette transporter encoded by the genes nrtA, nrtB, nrtC, and nrtD mediates active transport of nitrate and nitrite, which is inhibited by ammonium, a preferred source of nitrogen for the cyanobacterium. One of the ATP-binding subunits of the transporter, NrtC, has a distinct C-terminal domain of 380 amino acid residues. A mutant NC2, constructed by removal of this domain using genetic engineering techniques, assimilated low concentrations of nitrate and nitrite and accumulated nitrate intracellularly, showing that the domain is not essential for the transporter activities. Assimilation of low concentrations of nitrite was only partially inhibited by ammonium in NC2 but was completely inhibited in the wild-type cells. Cells of NC2 and its derivative (nitrate reductase-less strain NC4) carrying the truncated NrtC but not the cells with the wild-type NrtC accumulated nitrate intracellularly in the presence of ammonium in medium. These findings indicated that the C-terminal domain of NrtC is involved in the ammonium-promoted inhibition of the nitrate/nitrite transporter. In the presence of ammonium, NC2 could not assimilate nitrate despite its ability to accumulate nitrate intracellularly, which suggested that reduction of intracellular nitrate by nitrate reductase is also subject to inhibition by ammonium.
...
PMID:Involvement of the C-terminal domain of an ATP-binding subunit in the regulation of the ABC-type nitrate/nitrite transporter of the Cyanobacterium synechococcus sp. strain PCC 7942. 934 Nov 63

Recombinant Arabidopsis thaliana NADH:nitrate reductase (NR; EC 1.6.6.1) was produced in the methylotrophic yeast Pichia pastoris and purified to near-electrophoretic homogeneity. Purified enzyme had the spectral and kinetic properties typical of highly purified NR from natural plant sources. Site-directed mutagenesis altering several key residues and regions was carried out, and the mutant enzyme forms were expressed in P. pastoris. When the invariant cysteine residue, cysteine-191, in the molybdo-pterin region of the A. thaliana NIA2 protein was replaced with serine or alanine, the NR protein was still produced but was inactive, showing that this residue is essential for enzyme activity. Deletions or substitutions of the conserved N terminus of NR retained activity and the ability to be inactivated in vitro when incubated with ATP. Enzyme with a histidine sequence appended to the N terminus was still active and was easily purified using metal-chelate affinity chromatography. These results demonstrate that P. pastoris is a useful and reliable system for producing recombinant holo-NR from plants.
...
PMID:Analysis of wild-type and mutant plant nitrate reductase expressed in the methylotrophic yeast Pichia pastoris. 939 Apr 42

Plant 3-hydroxy-3-methylglutaryl-CoA reductase(HMGR; EC 1.1.1.34) and sucrose-phosphate synthase (SPS; EC 2.4.1.14) and synthetic peptides designed from the known phosphorylation sites of plant HMGR (SAMS*: KSHMKYNRSTKDVK), rat acetyl-CoA carboxylase (SAMS: HMRSAMSGLHLVKRR), spinach SPS (SP2: GRRJRRISSVEJJDKK), and spinach NADH:nitrate reductase (NR6: GPTLKRTASTPFJNTTSK) were used to characterize kinase activities from cauliflower (Brassica oleracea L. ) inflorescences. The three major peaks of protein kinase activity resolved by anion-exchange FPLC are homologs of those observed previously in spinach leaves and thus are designated PKI, PKIV, and PKIII, listed in order of elution. PKIV was the most active in terms of phosphorylation and inactivation of recombinant Nicotiana HMGR and was also strictly Ca2+ dependent. The novel aspects are that PKIII has not been detected in previous cauliflower studies, that SAMS* is a more specific peptide substrate to identify potential HMGR kinases, and that the major HMGR kinase in cauliflower is Ca2+ dependent. Of the three major kinases that phosphorylated the SP2 peptide only PKI (partially Ca2+ sensitive) and PKIII (Ca2+ insensitive) inactivated native spinach leaf SPS. Cauliflower extracts contained endogenous SPS that was inactivated by endogenous kinase(s) in an ATP-dependent manner and this may be one of the substrate target proteins for PKI and/or PKIII. The substrate specificity of the three kinase peaks was studied using synthetic peptide variants of the SP2 sequence. All three kinases had a strong preference for peptides with a basic residue at P-6 (as in SP2 and SAMS*; SAMS has a free amino terminus at this position) or a Pro at P-7 (as in NR6). This requirement for certain residues at P-6 or P-7 was not recognized in earlier studies but appears to be a general requirement. In plant HMGR, a conserved His residue at P-6 is involved directly in catalysis and this may explain why substrates reduced HMGR phosphorylation in vitro.
...
PMID:3-Hydroxy-3-methylglutaryl-coenzyme A reductase kinase and sucrose-phosphate synthase kinase activities in cauliflower florets: Ca2+ dependence and substrate specificities. 967 40

Transposon mutagenesis of Staphylococcus carnosus led to the identification of three genes, modABC, which encode an ABC transporter that is involved in molybdate transport. It was shown by [14C]palmitate labeling that ModA represents a lipoprotein that in gram-positive bacteria is the counterpart of the periplasmic binding proteins of gram-negative organisms. The sequence characteristics identify ModB as the integral-membrane, channel-forming protein and ModC as the ATP-binding energizer for the transport system. Mutants defective in modABC had only 0.4% of the wild-type nitrate reductase activity. Molybdate at a non-physiologically high concentration (100 microM) fully restored nitrate reductase activity, suggesting that at least one other system is able to transport molybdate, but with lower affinity. The expression of modA (and most likely of modBC) was independent of oxygen and nitrate. To date, there are no indications for molybdate-specific regulation of modABC expression since in a modB mutant, modA expression was unchanged in comparison to the wild-type.
...
PMID:Characterization of the molybdate transport system ModABC of Staphylococcus carnosus. 1041 72

This study provides preliminary evidence that NO production could be a general attribute of algae. Anabaena doliolum was found to be a better NO producer than Scenedesmus and Synechoccocus. Experiments conducted with inhibitors of photosynthesis (DCMU), ATP synthesis (DCCD), and the uncoupler (2,4-DNP) and its analog arsenate clearly revealed that inhibition of nitrite assimilation through the blockage of nitrite reductase (NiR) is primarily responsible for NO emission. A linear relationship between nitrite concentration in the culture medium and NO in the exhaust gas supports the view that accumulation of nitrite is responsible for NO formation. A failure of Scenedesmus, grown in the medium substituted with W for Mo, to produce either NO/NO-2 in light or a 'light-off' peak, and a resumption of these activities upon the addition of Mo proved beyond doubt that a functional nitrate reductase (NR) is necessary for the production of nitrite and NO by algae grown on nitrate as the nitrogen source. Moreover, the appearance of a NO peak immediately after nitrite supplementation under dark conditions in W-substituted cultures with or without glucose ruled out an enzymatic role of NR in NO emission.
...
PMID:Studies on nitric oxide (NO) formation by the green alga Scenedesmus obliquus and the diazotrophic cyanobacterium Anabaena doliolum. 1052 Apr 83

Outward-rectifying K+ channels are modulated in response to environmental stimuli by a range of intracellular factors, such as cytoplasmic Ca2+, pH, kinases and phosphatases. Here we report that voltage-dependent outward-rectifying K+ channels in tomato cells are also targets for modulation by 14-3-3 proteins. In whole-cell patch-clamp experiments, recombinant 14-3-3 protein (tomato isoform TFT7) was introduced into tomato cell protoplasts via the patch pipette. As a result the steady-state outward K+ current increased twofold and this increase was not dependent upon the presence of cytoplasmic ATP. A phosphorylated peptide that contained a phosphorylated 14-3-3 target-binding motif (RSTS*TP), derived from nitrate reductase, blocked the effect of 14-3-3, thus showing the specific nature of 14-3-3 action. Kinetic parameters of the conductance, like (de)activation kinetics, voltage dependence of gating and activation potential, were not significantly different between control and 14-3-3 infused cells. Analysis of single-channel activity and whole-cell noise indicated that the single-channel conductance was not affected by 14-3-3 infusion. We conclude that 14-3-3 proteins recruit 'sleepy' channels into a voltage-activatable state. The molecular mechanism underlying the 1 : 1 ratio of constitutively active and 14-3-3 recruited channels is discussed in the light of known functions of 14-3-3 dimers.
...
PMID:14-3-3 proteins double the number of outward-rectifying K+ channels available for activation in tomato cells 1065 39

Despite 14-3-3 proteins being implicated in the control of the eukaryotic cell cycle, metabolism, cell signalling and survival, little is known about the global regulation or functions of the phosphorylation-dependent binding of 14-3-3s to diverse target proteins. We identified Arabidopsis cytosolic proteins that bound 14-3-3s in competition with a 14-3-3-binding phosphopeptide, including nitrate reductase, glyceraldehyde- 3-phosphate dehydrogenase, a calcium-dependent protein kinase, sucrose-phosphate synthase (SPS) and glutamyl-tRNA synthetase. Remarkably, in cells starved of sugars or fed with non-metabolizable glucose analogues, all 14-3-3 binding was lost and the target proteins were selectively cleaved into proteolytic fragments. 14-3-3 binding reappeared after several hours of re-feeding with sugars. Starvation-induced degradation was blocked by 5-amino imidazole-4-carboxamide riboside (which is converted to an AMP-mimetic) or the protease inhibitor MG132 (Cbz-leu-leu-leucinal). Extracts of sugar-starved (but not sugar-fed) Arabidopsis cells contained an ATP-independent, MG132-sensitive, neutral protease that cleaved Arabidopsis SPS, and the mammalian 14-3-3-regulated transcription factor, FKHR. Cleavage of SPS and phosphorylated FKHR in vitro was blocked by binding to 14-3-3s. The finding that 14-3-3s participate in a nutrient-sensing pathway controlling cleavage of many targets may underlie the effects of these proteins on plant development.
...
PMID:14-3-3s regulate global cleavage of their diverse binding partners in sugar-starved Arabidopsis cells. 1085 32

The activity of nitrate reductase (+Mg(2+), NR(act)) in illuminated leaves from spinach, barley and pea was 50-80% of the maximum activity (+EDTA, NR(max)). However, NR from leaves of Ricinus communis L. had a 10-fold lower NR(act), while NR(max) was similar to that in spinach leaves. The low NR(act) of Ricinus was independent of day-time and nitrate nutrition, and varied only slightly with leaf age. Possible factors in Ricinus extracts inhibiting NR were not found. NR(act) from Ricinus, unlike the spinach enzyme, was very low at pH 7.6, but much higher at more acidic pH with a distinct maximum at pH 6.5. NR(max) had a broad pH response profile that was similar for the spinach and the Ricinus enzyme. Accordingly, the Mg(2+)-sensitivity of NR from Ricinus was strongly pH-dependent (increasing sensitivity with increasing pH), and as a result, the apparent activation state of NR from a Ricinus extract varied dramatically with pH and Mg(2+)concentration. Following a light-dark transition, NR(act) from Ricinus decreased within 1 h by 40%, but this decrease was paralleled by NR(max). In contrast to the spinach enzyme, Ricinus-NR was hardly inactivated by incubating leaf extracts with ATP plus okadaic acid. A competition analysis with antibodies against the potential 14-3-3 binding site around ser 543 of the spinach enzyme revealed that Ricinus-NR contains the same site. Removal of 14-3-3 proteins from Ricinus-NR by anion exchange chromatography, activated spinach-NR but caused little if any activation of Ricinus-NR. It is suggested that Mg(2+)-inhibition of Ricinus-NR does not require 14-3-3 proteins. The rather slow changes in Ricinus-NR activity upon a light/dark transient may be mainly due to NR synthesis or degradation.
...
PMID:Nitrate reductases from leaves of Ricinus (Ricinus communis L.) and spinach (Spinacia oleracea L.) have different regulatory properties. 1094 37

The nitrate reductase activity from Chlamydomonas reinhardtii was not altered when extracts were incubated with yeast 14-3-3 proteins in the presence of Mg-ATP. However, the C. reinhardtii extracts contained 14-3-3 proteins capable of inhibiting the spinach nitrate reductase, raising the question of their physiological substrates. Two C. reinhardtii proteins of about 48 and 35 kDa were eluted from 14-3-3 affinity chromatography columns and bound to 14-3-3s in overlay assays. The 48-kDa protein corresponded to the cytosolic isoform of glutamine synthetase (GS1). The GSI was phosphorylated by a Ca2+-and calmodulin-dependent protein kinase partially purified from the alga. However, neither phosphorylation nor 14-3-3 binding seemed to change GS catalytic activity.
...
PMID:Cytosolic glutamine synthetase and not nitrate reductase from the green alga Chlamydomonas reinhardtii is phosphorylated and binds 14-3-3 proteins. 1121 47


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

---