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)

Dimethyl sulfide dehydrogenase from the purple phototrophic bacterium Rhodovulum sulfidophilum catalyzes the oxidation of dimethyl sulfide to dimethyl sulfoxide. Recent DNA sequence analysis of the ddh operon, encoding dimethyl sulfide dehydrogenase (ddhABC), and biochemical analysis (1) have revealed that it is a member of the DMSO reductase family of molybdenum enzymes and is closely related to respiratory nitrate reductase (NarGHI). Variable temperature X-band EPR spectra (120-122 K) of purified heterotrimeric dimethyl sulfide dehydrogenase showed resonances arising from multiple redox centers, Mo(V), [3Fe-4S](+), [4Fe-4S](+), and a b-type heme. A pH-dependent EPR study of the Mo(V) center in (1)H(2)O and (2)H(2)O revealed the presence of three Mo(V) species in equilibrium, Mo(V)-OH(2), Mo(V)-anion, and Mo(V)-OH. Above pH 8.2 the dominant species was Mo(V)-OH. The maximum specific activity occurred at pH 9.27. Comparison of the rhombicity and anisotropy parameters for the Mo(V) species in DMS dehydrogenase with other molybdenum enzymes of the DMSO reductase family showed that it was most similar to the low-pH nitrite spectrum of Escherichia coli nitrate reductase (NarGHI), consistent with previous sequence analysis of DdhA and NarG. A sequence comparison of DdhB and NarH has predicted the presence of four [Fe-S] clusters in DdhB. A [3Fe-4S](+) cluster was identified in dimethyl sulfide dehydrogenase whose properties resembled those of center 2 of NarH. A [4Fe-4S](+) cluster was also identified with unusual spin Hamiltonian parameters, suggesting that one of the iron atoms may have a fifth non-sulfur ligand. The g matrix for this cluster is very similar to that found for the minor conformation of center 1 in NarH [Guigliarelli, B., Asso, M., More, C., Augher, V., Blasco, F., Pommier, J., Giodano, G., and Bertrand, P. (1992) Eur. J. Biochem. 307, 63-68]. Analysis of a ddhC mutant showed that this gene encodes the b-type cytochrome in dimethyl sulfide dehydrogenase. Magnetic circular dichroism studies revealed that the axial ligands to the iron in this cytochrome are a histidine and methionine, consistent with predictions from protein sequence analysis. Redox potentiometry showed that the b-type cytochrome has a high midpoint redox potential (E degrees = +315 mV, pH 8).
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PMID:Characterization of the redox centers in dimethyl sulfide dehydrogenase from Rhodovulum sulfidophilum. 1248 61

Hydrophobic membrane proteins often have complex functions and are thus of great interest. However, their analysis presents a challenge because they are not readily soluble in polar solvents and often undergo aggregation. We present a sequential CNBr and trypsin in-gel digestion method combined with mass spectrometry for membrane protein analysis. CNBr selectively cleaves methionine residues. But due to the low number of methionines in proteins, CNBr cleavage produces a small number of large peptide fragments with MWs typically >2000, which are difficult to extract from gel pieces. To produce a larger number of smaller peptides than that obtained by using CNBr alone, we demonstrate that trypsin can be used to further digest the sample in gel. The use of n-octyl glucoside (n-OG) to enhance the digestion efficiency and peptide recovery was also studied. We demonstrate that the sensitivity of this membrane protein identification method is in the tens of picomole regime, which is compatible to the Coomassie staining gel-spot visualization method, and is more sensitive than other techniques reported in the literature. This CNBr/trypsin in-gel digestion method is also found to be very reproducible and has been successfully applied for the analysis of complex protein mixtures extracted from biological samples. The results are presented from a study of the analysis of bacteriorhodopsin, nitrate reductase 1 gamma chain, and a complex protein mixture extracted from the endoplasmic recticulum membrane of mouse liver.
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PMID:Development and applications of in-gel CNBr/tryptic digestion combined with mass spectrometry for the analysis of membrane proteins. 1458 51

A pot experiment was conducted to evaluate the effects of applying L-methionine (L-MET), L-phenylalanine (LPHE) and L-tryptophan (L-TRP) on the growth of Zea mays and its nutrient uptake, and to determine the optimal application rate of them. The results showed that L-MET, L-PHE and L-TRP could improve the shoot height, shoot and root dry weights, root activity, nitrate reductase and hydrogen peroxidase activities, and N, P, K and Zn uptake of corn. The optimal application rate of L-MET, L- PHE and L-TRP was 0.0185 - 0.185 mg x kg)(-1) soil, 0.2 mg x kg(-1) soil, and 0.03 - 0.3 mg x kg(-1) soil, respectively, and L-PHE and L-TRP were superior to L-MET.
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PMID:[Effects of applying L-methionine, L-phenylalanine and L-tryptophan on Zea mays growth and its nutrient uptake]. 1618 Jul 48

The induction of nitrate reductase activity in root tips of cotton (Gossypium hirsutum L.) was regulated by several amino acids and by ammonium. Glycine, glutamine, and asparagine strongly inhibited induction of activity by nitrate and also decreased growth of sterile-cultured roots on a nitrate medium. Methionine, serine, and alanine weakly inhibited induction, and 11 other amino acids had little or no effect. Ammonium also decreased induction in root tips, but was most effective only at pH 7 or higher. The optimum conditions for ammonium regulation of induction were identical to those for growth of sterile-cultured roots on ammonium as the sole nitrogen source. Aspartate and glutamate strongly stimulated induction, but several lines of evidence indicated that the mechanism of this response was different from that elicited by the other amino acids. The effects of amino acids on induction appeared to be independent of nitrate uptake.In green shoot tissues, all attempts to demonstrate regulation of induction by amino acids failed. The great difference in observed responses of root and shoot to amino acids suggests that their nitrate reductase activities are regulated differently. Differential regulation of this enzyme is consistent with the responses of root and shoot nitrate reductase activity to nitrate.
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PMID:Differential regulation of nitrate reductase induction in roots and shoots of cotton plants. 1665 46

Excised 7-day-old oat (Avena sativa L. cv. Jaycee) leaves were incubated in media containing 7.1 millimolar KNO(3) and 0.15 millimolar tabtoxin or 1 millimolar methionine sulfoximine (MSO) to investigate the sources of the observed ammonium accumulated. Tabtoxin and MSO are known inhibitors of glutamine synthetase, the first enzyme in the primary pathway of ammonium assimilation. During a 4- to 6-hour incubation, there was little net change in protein or total amino acid concentration. Alanine, aspartate/asparagine, and glutamate/glutamine decreased markedly under these treatments, whereas several other amino acids increased. Exogenous (15)N from K(15)NO(3) was taken up and incorporated into the nitrate and ammonium fractions of leaves treated with tabtoxin or MSO. This result and the high in vitro activities of nitrate reductase indicated that reduction of nitrate was one source of the accumulated ammonium. Leaves incubated under 2% O(2) to reduce photorespiration accumulated only about 13% as much ammonium as did those under normal atmospheres. We conclude that most of the tabtoxin- or MSO-induced ammonium came from photo-respiration, and the remainder was from nitrate reduction.
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PMID:Sources of ammonium in oat leaves treated with tabtoxin or methionine sulfoximine. 1666 6

The effects of ammonium application on nitrate utilization were studied in N-limited cultures of Lemna gibba L. G3. Addition of ammonium instantaneously inhibited net nitrate uptake by at least 60%, followed by a slight recovery. The inhibition was equally clear after near-complete inactivation of glutamine synthetase by application of l-methionine-d,l-sulfoximine. Experiments where (13)N-labeled nitrate was used as an influx tracer revealed that ammonium specifically inhibited influx, but did not promote nitrate efflux. Nitrate accumulation was relatively more inhibited than nitrate reduction and net uptake. Nitrate reductase, extracted and assayed in vitro in the presence of the thiol proteinase inhibitor leupeptin, was unaffected by short-term treatment of the plants with either nitrate, ammonium, or ammonium nitrate. Nitrate reductase activity recovered in the absence of leupeptin was considerably lower; however, it was enhanced by all the nitrogen sources, with ammonium as the most potent. It is argued that the effect of ammonium on nitrate utilization in Lemna is due to inhibition of nitrate influx, and that the effect should be attributed to ammonium itself, not to a newly formed nitrogen derivative. The decreased nitrate flux caused a decrease in nitrate reduction, whereas the activity of nitrate reductase per se rather is stabilized by presence of ammonium.
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PMID:Nitrogen Utilization in Lemna: III. Short-Term Effects of Ammonium on Nitrate Uptake and Nitrate Reduction. 1666 92

Chlorella autotrophica, a euryhaline marine alga, and Stichococcus bacillaris, a salt-tolerant soil alga, grow in the presence of methionine sulfoximine (MSX), an inhibitor of glutamine synthetase, by maintaining high levels of NADPH-glutamate dehydrogenase. Nitrate reductase showed no change in MSX-adapted cells. For both species, MSX-adapted cells retained their capacity to accumulate proline in response to salinity, and in S. bacillaris no major shift was observed in the presence of MSX toward the accumulation of sorbitol. Following transfer from 33 to 150% artificial seawater (ASW), both algae exhibited increases in organic solute levels without a lag. Within 6 h of this sudden increase in salinity, the levels of proline in C. autotrophica and of proline and sorbitol in S. bacillaris were similar to those found in steady state 150% ASW cultures. Following transfer from 33 to 150% ASW, S. bacillaris continued [(14)C] bicarbonate photoassimilation at a normal rate and maintained active enzymes of nitrogen assimilation. The incorporation of [(14)C]phenylalanine into proteins was inhibited for about 30 minutes in MSX-free cells and 90 minutes in MSX-adapted cells following transfer from 33 to 150% ASW; the recovery after these lag periods was almost complete.
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PMID:The Relationship between Inorganic Nitrogen Metabolism and Proline Accumulation in Osmoregulatory Responses of Two Euryhaline Microalgae. 1666 6

Detached first leaves of 3-day-old corn seedlings (Zea mays L. W64AxW183E) were incubated with nitrate in air or 100% O(2) in the light. Nitrate accumulation in the leaves was not depressed by O(2). NADH:nitrate reductase activity and enzyme protein, as measured with an enzyme-linked immunosorbent assay, increased in parallel during the 8 h nitrate treatment in air, but in O(2) the levels of enzyme activity and protein were depressed. NADH:nitrate reductase mRNA levels were the same in the air-and O(2)-treated leaves. Total soluble protein levels in leaves were slightly depressed by O(2) and shifting from O(2) to an air environment increased the protein level. Incorporation of [(35)S]methionine during nitrate treatment revealed that total soluble protein and nitrate reductase protein synthesis were both depressed by the O(2) environment relative to air, but both recovered when leaves were shifted from O(2) to air. Although O(2) accelerated inactivation of nitrate reductase in vitro, the in vivo inactivation rate appeared to be too low to account for the depressed level of nitrate reductase activity in O(2)-treated leaves. We concluded that O(2) inhibition of nitrate reductase biosynthesis in detached corn leaves was largely due to inhibition of total soluble protein synthesis at the level of translation.
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PMID:Oxygen Inhibition of Nitrate Reductase Biosynthesis in Detached Corn Leaves via Inhibition of Total Soluble Protein Synthesis. 1666 52

Aspartate kinase (AK, EC 2.7.2.4), homoserine dehydrogenase (HSDH, EC 1.1.1.3) and dihydrodipicolinate synthase (DHDPS, EC 4.2.1.52) were isolated and partially purified from immature Chenopodium quinoa Willd seeds. Enzyme activities were studied in the presence of the aspartate-derived amino acids lysine, threonine and methionine and also the lysine analogue S-2-aminoethyl-l-cysteine (AEC), at 1 mM and 5 mM. The results confirmed the existence of, at least, two AK isoenzymes, one inhibited by lysine and the other inhibited by threonine, the latter being predominant in quinoa seeds. HSDH activity was also shown to be partially inhibited by threonine, whereas some of the activity was resistant to the inhibitory effect, indicating the presence of two isoenzymes, one resistant and another sensitive to threonine inhibition. Only one DHDPS isoenzyme highly sensitive to lysine inhibition was detected. The results suggest that the high concentration of lysine observed in quinoa seeds is possibly due to a combined effect of increased lysine synthesis and accumulation in the soluble form and/or as protein lysine. Nitrogen assimilation was also investigated and based on nitrate content, nitrate reductase activity, amino acid distribution and ureide content, the leaves were identified as the predominant site of nitrate reduction in this plant species. The amino acid profile analysis in leaves and roots also indicated an important role of soluble glutamine as a nitrogen transporting compound.
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PMID:Lysine biosynthesis and nitrogen metabolism in quinoa (Chenopodium quinoa): study of enzymes and nitrogen-containing compounds. 1800 25

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


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