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Query: EC:1.7.1.4 (nitrite reductase)
 1,847 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Prochlorococcus is one of the dominant cyanobacteria and a key primary producer in oligotrophic intertropical oceans. Here we present an overview of the pathways of nitrogen assimilation in Prochlorococcus, which have been significantly modified in these microorganisms for adaptation to the natural limitations of their habitats, leading to the appearance of different ecotypes lacking key enzymes, such as nitrate reductase, nitrite reductase, or urease, and to the simplification of the metabolic regulation systems. The only nitrogen source utilizable by all studied isolates is ammonia, which is incorporated into glutamate by glutamine synthetase. However, this enzyme shows unusual regulatory features, although its structural and kinetic features are unchanged. Similarly, urease activities remain fairly constant under different conditions. The signal transduction protein P(II) is apparently not phosphorylated in Prochlorococcus, despite its conserved amino acid sequence. The genes amt1 and ntcA (coding for an ammonium transporter and a global nitrogen regulator, respectively) show noncorrelated expression in Prochlorococcus under nitrogen stress; furthermore, high rates of organic nitrogen uptake have been observed. All of these unusual features could provide a physiological basis for the predominance of Prochlorococcus over Synechococcus in oligotrophic oceans.
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PMID:Streamlined regulation and gene loss as adaptive mechanisms in Prochlorococcus for optimized nitrogen utilization in oligotrophic environments. 1559 Jul 77

The Synechocystis sp. strain PCC 6803 mutant deficient in PII protein (the glnB gene product) was found to express glutamine synthetase activity at levels several times higher than the wild-type strain. There was no significant difference in nitrate reductase activity levels between the two strains, and the nitrite reductase levels were somewhat lower in the mutant than in the wild-type strain. The higher glutamine synthetase activity in the mutant was ascribed to higher expression levels of the glutamine synthetase genes (glnA and glnN), which belong to the regulon controlled by NtcA, a Crp-family transcription regulator. Examination of the effects of PII deficiency on other NtcA-regulated genes revealed that the transcript levels of amt1 (encoding an ammonium permease) and gifB (encoding an inhibitor of glutamine synthetase) were increased, whereas that of gifA (a homolog of gifB, encoding another glutamine synthetase inhibitor) was decreased, with those of nirA, nrtC, icd, sigE (rpoD2-V), nblA and ntcA being unaffected. Unlike the Synechococcus elongatus strain PCC 7942, induction or repression of the NtcA-regulated genes proceeded normally in the PII-deficient mutant upon nitrogen depletion. The altered steady-state expression levels of glnA, glnN, amt1, gifA and gifB in the PII-deficient mutant suggested that Synechocystis sp. strain PCC 6803 has a mechanism for regulation of the subset of the NtcA-regulated genes related directly to ammonium assimilation.
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PMID:Effects of PII deficiency on expression of the genes involved in ammonium utilization in the cyanobacterium Synechocystis sp. Strain PCC 6803. 1654 96

The catabolism of nuclear-encoded stromal proteins was investigated in intact chloroplasts isolated mechanically from pea (Pisum sativum) leaves. Glutamine synthetase, phosphoribulokinase, and nitrite reductase (quantified by immunoblotting) were more rapidly degraded in the light than in the dark. Furthermore, the degradation rates depended on exogenously supplied metabolites. For example, 2-oxoglutarate accelerated the catabolism of all three enzymes in chloroplasts incubated in the light, whereas oxaloacetate stabilized glutamine synthetase and at the same time destabilized the other two enzymes.
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PMID:Effects of light and external solutes on the catabolism of nuclear-encoded stromal proteins in intact chloroplasts isolated from pea leaves. 1665 46

Density gradient separation of plastids from leaf and root tissue was carried out. The distribution in the gradients of the activity of the following enzymes was determined: nitrite reductase, glutamine synthetase, acetolactate synthetase, aspartate aminotransferase, catalase, cytochrome oxidase, and triosephosphate isomerase. The distribution of chlorophyll was followed in gradients from leaf tissue. The presence of plastids that have retained their stroma enzymes was denoted by a peak of triosephosphate isomerase activity. Coincidental with this peak were bands of nitrite reductase, acetolactate synthetase, glutamine synthetase, and aspartate aminotransferase activity. The results suggest that most, if not all, the nitrite reductase and acetolactate synthetase activity of the cell is in the plastids. The plastids were found to contain only part of the total glutamine synthetase, aspartate aminotransferase, and triosephosphate dehydrogenase activity in the cell. Some evidence was obtained for low levels of glutamate dehydrogenase activity in chloroplasts.
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PMID:The location of nitrite reductase and other enzymes related to amino Acid biosynthesis in the plastids of root and leaves. 1665 26

Intercellular distribution of enzymes involved in amino nitrogen synthesis was studied in leaves of species representing three C(4) groups, i.e. Sorghum bicolor, Zea mays, Digitaria sanguinalis (NADP malic enzyme type); Panicum miliaceum (NAD malic enzyme type); and Panicum maximum (phosphoenolpyruvate carboxykinase type). Nitrate reductase, nitrite reductase, glutamine synthetase, and glutamate synthase were predominantly localized in mesophyll cells of all the species, except in P. maximum where nitrite reductase had similar activity on a chlorophyll basis, in both mesophyll and bundle sheath cells. NADH-glutamate dehydrogenase was concentrated in the bundle sheath cells, while NADPH-glutamate dehydrogenase was localized in both mesophyll and bundle sheath cells. The activities of nitrate-assimilating enzymes, except for nitrate reductase, were high enough to account for the proposed in vivo rates of nitrate assimilation.Based on the differential centrifugation of cell homogenates of P. miliaceum, mesophyll chloroplasts appear to be the major site of nitrate assimilation since nitrite reductase, glutamine synthetase, glutamate synthase, and NADPH-glutamate dehydrogenase were primarily localized in the chloroplast fraction. Both the glutamine synthetase-glutamate synthase and glutamate dehydrogenase pathways were considered as alternative routes of amino nitrogen synthesis.
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PMID:Distribution of Nitrate-assimilating Enzymes between Mesophyll Protoplasts and Bundle Sheath Cells in Leaves of Three Groups of C(4) Plants. 1665 90

The effects of nitrogen source NO(3) (-) or NH(4) (+) on nitrogen metabolism during the first 2 weeks of germination of the rice seedling (Oryza sativa L., var. IR22) grown in nutrient solution containing 40 mug/ml N were studied. Total, soluble protein, and free amino N levels were higher in the NH(4) (+)-grown seedling, particularly during the 1st week of germination. Asparagine accounted for most of the difference in free amino acid level, in both the root and the shoot. Nitrate and nitrite reductase activities were present mainly in the shoot and were higher in the NO(3) (-)-grown seedling, whereas the activity of glutamate dehydrogenase and glutamine synthetase in the root tended to be lower than that of the NH(4) (+)-grown seedling during the 1st week of germination. Glycolate oxidase and catalase activities were present mainly in the shoot. Maximum activity of the above five enzymes occurred 7 to 10 days after germination. Differences in the zymograms of nitrate reductase, glutamate dehydrogenase, and catalase were mainly between shoot and root and not from N source. Nitrite reductase bands were observed only in plants grown in plants grown in NO(3) (-).Ten-day-old seedlings of three rices differing in level of grain protein did not differ in the level of N fractions and of enzyme activities, which were consistent with their differences in grain protein content.
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PMID:Aspects of nitrogen metabolism in the rice seedling. 1665

Chloroplasts were prepared from peas (Pisum sativum) in glucose-phosphate medium. In the presence of dl-glyceraldehyde, they catalyzed nitrite-dependent O(2) evolution (mean of 13 preparations, 17.5 mumole per mg chlorophyll per hour, sd 3.64). The optimum concentration of nitrite was 0.5 mm; 0.12 mm nitrite supported V(max)/2. The reaction was accompanied by the consumption of nitrite; 55 to 80% of the nitrite-N consumed was recovered as ammonia. In short experiments (less than 10 minutes) the O(2) to nitrite ratio approached 1.5, but thereafter decreased. There was no nitrite-dependent O(2) evolution with chloroplasts from plants grown without added nitrate but such chloroplasts could assimilate ammonia at about the usual rate. The results are consistent with the reduction of nitrite to ammonia involving nitrate-induced nitrite reductase and a reductant generated by the chloroplast electron transport chain.In the presence of ADP, pyrophosphate, and MgCl(2) the O(2) to nitrite ratio was typically 0.5 to 0.6 and the recovery of nitrite-N as ammonia about 60%. Under these conditions, alpha-ketoglutarate increased the O(2) to nitrite ratio (0.9-1.35) and the recovery of nitrite-N as ammonia decreased to 27%. These data and the results of nitrite plus ammonia addition experiments (with and without alpha-ketoglutarate) are attributed to incorporation of nitrite-N into glutamate via the chloroplast enzymes nitrite reductase, glutamine synthetase, and glutamate synthetase.
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PMID:Light-dependent Assimilation of Nitrite by Isolated Pea Chloroplasts. 1666 Mar 65

Cell organelles have been isolated from protoplast lysates and total homogenates obtained from root tips of Pisum sativum L. (cv Little Marvel) and Medicago media Pers. (cv Saranac) grown in hydroponics with nitrate nutrient solutions. Density-gradient and differential centrifugation procedures have been used to prepare mitochondria-and plastid-enriched fractions in which glutamine synthetase (GS) activity was estimated. Even when purified protoplasts were gently ruptured, significant breakage of plastids occurred during preparation as shown by the high proportion of nitrite reductase recovered in the soluble fraction. Of the total GS activity recovered, up to 20% was associated with the plastid fraction, depending on the source of plant material and the GS assay utilized; when corrected for recovery of the plastid marker nitrite reductase, it was calculated that 15 to 57% of alfalfa and 14 to 64% of pea root GS was located in the plastids. A true biosynthetic assay in which glutamine production was monitored by high performance liquid chromatography was devised to estimate the physiological significance of the transferase and the semibiosynthetic assays currently used for activity measurements. When compared with the true and semibiosynthetic assays, the transferase assay for GS appeared to underestimate the root plastid enzyme. Root plastid GS was partially purified by ion-exchange chromatography, and results show that the isoenzyme found in root plastids is different from chloroplastic or cytosolic GS.
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PMID:Isoenzymes of Glutamine Synthetase in Roots of Pea (Pisum sativum L. cv Little Marvel) and Alfalfa (Medicago media Pers. cv Saranac). 1666 16

The specific activities of nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase were determined in intact protoplasts and intact chloroplasts from Chlamydomonas reinhardtii. After correction for contamination, the data were used to calculate the portion of each enzyme in the algal chloroplast. The chloroplast of C. reinhardtii contained all enzyme activities for nitrogen assimilation, except nitrate reductase, which could not be detected in this organelle. Glutamate synthase (NADH- and ferredoxin-dependent) and glutamate dehydrogenase were located exclusively in the chloroplast, while for nitrite reductase and glutamine synthetase an extraplastidic activity of about 20 and 60%, respectively, was measured. Cells grown on ammonium, instead of nitrate as nitrogen source, had a higher total cellular activity of the NADH-dependent glutamate synthase (+95%) and glutamate dehydrogenase (+33%) but less activity of glutamine synthetase (-10%). No activity of nitrate reductase could be detected in ammonium-grown cells. The distribution of nitrogen-assimilating enzymes among the chloroplast and the rest of the cell did not differ significantly between nitrate-grown and ammonium-grown cells. Only the plastidic portion of the glutamine synthetase increased to about 80% in cells grown on ammonium (compared to about 40% in cells grown on nitrate).
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PMID:Localization of Nitrogen-Assimilating Enzymes in the Chloroplast of Chlamydomonas reinhardtii. 1666 9

The effect of nitrate application on glutamine synthetase activity in roots of pea (Pisum sativum L.) seedlings (2 weeks old) was studied. Separation of organelles from root fragments by sucrose density-gradient centrifugation revealed that both nitrite reductase and glutamine synthetase activities increased in root plastids as a response to nitrate application and that no such response was induced by ammonium application. Glutamine synthetase activity was also found to increase in plastids with distance from apex in nitrate-treated plants, the highest specific activity being located in the fourth 1-centimeter segment. Separation by SDS-PAGE and characterization by Western blotting showed that cytosolic glutamine synthetase contains one subunit polypeptide (28 kilodaltons) and that plastid glutamine synthetase contains both the 38-kilodalton subunit and a heavier subunit. When nitrate was present in the nutrient solution, the heavier subunit increased in abundance in protein fractions obtained from purified root plastids.
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PMID:Tissue and Cellular Distribution of Glutamine Synthetase in Roots of Pea (Pisum sativum) Seedlings. 1666 62


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