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

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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)

Two new loci have been found to be clustered with five other genes for the nitrate assimilation pathway in the Chlamydomonas reinhardtii genome. One gene, located close to the 3'-end of the high-affinity nitrate transporter (HANT) gene Nrt 2; 2, corresponds to the nitrite reductase (NiR) structural gene Nii1. This is supported by a number of experimental findings: (i) NiR-deficient mutants have lost Nii1 gene expression; (ii) Nii1 mRNA accumulation is co-regulated with the expression of other structural genes of the nitrate assimilation pathway; (iii) nitrite (nitrate) utilization ability is recovered in the NiR mutants by functional complementation with a wild-type Nii1 gene; (iv) the elucidated NII1 amino acid sequence is highly similar to that of the cyanobacterial and higher-plant enzyme, and contains the predicted domains for plastidic ferredoxin-NiRs. Thus, the mutant phenotype and the mRNA sequence and expression of the Nii1 gene have been unequivocally related. Accumulation of mRNA for the second locus identified. Lde1 (light-dependent expression), was not regulated by nitrogen, but like nitrate-assimilation clustered genes, its expression was down-regulated in the dark.
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PMID:Clustering of the nitrite reductase gene and a light-regulated gene with nitrate assimilation loci in Chlamydomonas reinhardtii. 973 4

We constructed mutant strains lacking the nitrite reductase (NR) gene in Chlamydomonas reinhardtii. Two types of NR mutants were obtained, which either have or lack the high-affinity nitrate transporter (Nrt2;1, Nrt2;2, and Nar2) genes. None of these mutants overexpressed nitrate assimilation gene transcripts nor NR activity in nitrogen-free medium, in contrast to NR mutants. This finding confirms the previous role proposed for NR on its own regulation (autoregulation) and on the other genes for nitrate assimilation in C. reinhardtii. In addition, the NR mutants were used to study nitrate transporters from nitrite excretion. At high CO(2), only strains carrying the above high-affinity nitrate transporter genes excreted stoichiometric amounts of nitrite from 100 microM nitrate in the medium. A double mutant, deficient in both the high-affinity nitrate transporter genes and NR, excreted nitrite at high CO(2) only when nitrate was present at mM concentrations. This suggests that there exists a low-affinity nitrate transporter that might correspond to the nitrate/nitrite transport system III. Moreover, under low CO(2) conditions, the double mutant excreted nitrite from nitrate at micromolar concentrations by a transporter with the properties of the nitrate/nitrite transport system IV.
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PMID:Nitrite reductase mutants as an approach to understanding nitrate assimilation in Chlamydomonas reinhardtii. 1063 Dec 72

Ferredoxin (Fd) from Chlamydomonas reinhardtii is composed of 94 amino-acid residues and a [2Fe-2S] cluster. The homology modelling technique has been used to predict the tertiary structure of C. reinhardtii Fd. The overall structure shows the typical fifth-stranded beta-grasp plus two additional beta-sheets and three alpha-helices. Site-directed mutagenesis of recombinant Fd has allowed us to obtain four point mutants and one double mutant--all mutations being located in the short alpha-helix at the carboxy-terminal segment as well as a triple mutant affected on helix alpha1. Crosslinking studies and measurement of enzymatic activities reveal that the residues changed are critical for the interaction of Fd with glutamate synthase (GOGAT) and nitrite reductase (NiR). Potentiometric analyses of the Fd mutants show that the replacement of glutamate in position 91 drastically changes the redox potential value (70 mV), thereby suggesting that such a glutamate can modulate the reactivity of Fd towards its reaction partners. According to results herein presented, the reported mutations modify the electrostatic interactions within the complex formed between Fd and GOGAT or NiR.
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PMID:Homology predicted structure and functional interaction of ferredoxin from the eukaryotic alga Chlamydomonas reinhardtii with nitrite reductase and glutamate synthase. 1112 98

The in situ localization of the chloroplast enzymes ribulose-1,5-bisphosphate carboxylase (Rubisco), Rubisco activase, ribose-5-phosphate isomerase, glyceraldehyde-3-phosphate dehydrogenase, aldolase, nitrite reductase, ferredoxin-NADP+ reductase, and H+-ATP synthase was studied by immunoelectron microscopy in Chlamydomonas reinhardtii. Immunogold labeling revealed that, despite Rubisco in the pyrenoid matrix, Calvin cycle enzymes, Rubisco activase, nitrite reductase, ferredoxin-NADP+ reductase, and H+-ATP synthase are associated predominantly with chloroplast thylakoid membranes and the inner surface of the pyrenoid membrane. This is in accord with previous enzyme localization studies in higher plants (K.H. Suss, C. Arkona, R. Manteuffel, K. Adler [1993] Proc Natl Acad Sci USA 90: 5514-5518). Pyrenoid tubules do not contain these enzymes. The pyrenoid matrix consists of Rubisco but is devoid of the other photosynthetic enzymes investigated. Evidence for the occurrence of two Rubisco forms differing in their spatial localization has also been obtained: Rubisco form I appears to be membrane associated like other Calvin cycle components, whereas Rubisco form II is confined to the pyrenoid matrix. It is proposed that enzyme form I represents an active Rubisco when assembled into Calvin cycle enzyme complexes, whereas Rubisco form II may be part of a CO2-concentrating mechanism. Pyrenoidal Calvin cycle complexes are thought to be highly active in CO2 fixation and important for the synthesis of starch around the pyrenoid.
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PMID:In Situ Association of Calvin Cycle Enzymes, Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Activase, Ferredoxin-NADP+ Reductase, and Nitrite Reductase with Thylakoid and Pyrenoid Membranes of Chlamydomonas reinhardtii Chloroplasts as Revealed by Immunoelectron Microscopy. 1222 43

Cadmium (Cd(2+)) or copper (Cu(2+)) ions are toxic for Chlamydomonas reinhardtii growth, at 300 microM, and the alga may accumulate about 0.90+/-0.02 and 0.64+/-0.02% of its dry weight, respectively. Metal contamination changes the elemental composition of dried alga biomass, which indicates the possibility to use C. reinhardtii as biosensor and bioremediator of the aquatic contamination by heavy metals. Either, Cd(2+) or Cu(2+), inhibits about 20% of the nitrate consumption rate by the cells, while only Cd(2+) increases about 40% the sulfate consumption rate. The presence of 1 mM calcium (Ca(2+)) in the culture medium increases the C. reinhardtii productivity (about 50%), the nitrate uptake rate (about 20%) and the sulfate uptake rate (about 30%). In addition, Ca(2+) overcomes the Cd(2+) (300 microM) toxicity by decreasing (about 35%) the intracellular accumulation of metal. Sulfur-starvation induces in C. reinhardtii the expression of serine acetyltransferase and O-acetylserine(thiol)lyase activities, but decreases 50% the consumption rate of nitrate by the cells. Sulfate is also required for the full expression of the nitrate reductase (NR), nitrite reductase (NiR) and glutamate synthase activities.
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PMID:Metal toxicity in Chlamydomonas reinhardtii. Effect on sulfate and nitrate assimilation. 1291 98

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 distribution of nitrite reductase (EC 1.7.7.1) in the green algae Chlamydomonas reinhardtii, Monoraphidium braunii, Chlorella fusca, and Scenedesmus obliquus was studied by immunoelectron microscopy. The labeling of ultrathin cryosections was performed with anti-nitrite reductase antibodies followed by gold-labeled goat anti-rabbit antibodies. In C. reinhardtii sections, gold label was mainly associated with the pyrenoid, tonoplast, and plasmalemma. Significant labeling was also detected in the thylakoid region. In all other organisms, label density was lower but distributed in the same locations, except that the plasmalemma of S. obliquus was not significantly labeled. From estimates of the relative volume of different cell regions, we found that approximately 80% of the total enzyme is located in the chloroplastic region (thylakoids plus pyrenoid) of C. reinhardtii, M. braunii, and C. fusca, and 97% in the case of S. obliquus.
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PMID:Immunocytochemical localization of nitrite reductase in green algae. 1666 45

In Chlamydomonas reinhardtii mutants defective at the structural locus for nitrate reductase (nit-1) or at loci for biosynthesis of the molybdopterin cofactor (nit-3, nit-4, or nit-5 and nit-6), both nitrite uptake and nitrite reductase activities were repressed in ammonium-grown cells and expressed at high amounts in nitrogen-free media or in media containing nitrate or nitrite. In contrast, wild-type cells required nitrate induction for expression of high levels of both activities. In mutants defective at the regulatory locus for nitrate reductase (nit-2), very low levels of nitrite uptake and nitrite reductase activities were expressed even in the presence of nitrate or nitrite. Both restoration of nitrate reductase activity in mutants defective at nit-1, nit-3, and nit-4 by isolating diploid strains among them and transformation of a structural mutant upon integration of the wild-type nit-1 gene gave rise to the wild-type expression pattern for nitrite uptake and nitrite reductase activities. Conversely, inactivation of nitrate reductase by tungstate treatment in nitrate, nitrite, or nitrogen-free media made wild-type cells respond like nitrate reductase-deficient mutants with respect to the expression of nitrite uptake and nitrite reductase activities. Our results indicate that nit-2 is a regulatory locus for both the nitrite uptake system and nitrite reductase, and that the nitrate reductase enzyme plays an important role in the regulation of the expression of both enzyme activities.
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PMID:Nitrate Reductase Regulates Expression of Nitrite Uptake and Nitrite Reductase Activities in Chlamydomonas reinhardtii. 1666 56

The RNA-binding protein CHLAMY1 from the green alga Chlamydomonas reinhardtii consists of two subunits. One (named C1) contains three lysine homology motifs and the other (named C3) has three RNA recognition motifs. CHLAMY1 binds specifically to uridine-guanine-repeat sequences and its circadian-binding activity is controlled at the posttranslational level, presumably by time-dependent formation of protein complexes consisting of C1 and C3 or C1 alone. Here we have characterized the role of the two subunits within the circadian system by measurements of a circadian rhythm of phototaxis in strains where C1 or C3 are either up- or down-regulated. Further, we have measured the rhythm of nitrite reductase activity in strains with reduced levels of C1 or C3. In case of changes in the C3 level (both increases and decreases), the acrophase of the phototaxis rhythm and of the nitrite reductase rhythm (C3 decrease) was shifted by several hours from subjective day (maximum in wild-type cells) back towards the night. In contrast, both silencing and overexpression of C1 resulted in disturbed circadian rhythms and arrhythmicity. Interestingly, the expression of C1 is interconnected with that of C3. Our data suggest that CHLAMY1 is involved in the control of the phase angle and period of the circadian clock in C. reinhardtii.
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PMID:A heteromeric RNA-binding protein is involved in maintaining acrophase and period of the circadian clock. 1692 Aug 78

Huge quantities of pesticides are dispersed in the environment, affecting non-target organisms. Since paraquat affects the photosynthetic process, the biochemical composition of affected species should be altered. The effect of paraquat on Chlamydomonas moewusii, a freshwater non-target species, was studied. After 48 h of herbicide exposure, growth rate, dry weight, and chlorophyll a and protein content were affected by paraquat concentrations above 0.05 microM. C/N ratio was also affected due to a decrease in nitrogen content in the dry biomass, while the carbon content remained constant for all paraquat concentrations assayed. Enzymes involved in nitrogen assimilation were affected by paraquat, being nitrate reductase activity more sensitive to paraquat than nitrite reductase. Based on the results obtained in the present study, paraquat exerts adverse effects upon a common freshwater green microalga, thus the application of this herbicide for weed control must be carried out very carefully, so that any disturbance affecting algae will have severe repercussions on higher trophic levels and on the elemental biogeochemical cycles.
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PMID:The herbicide paraquat induces alterations in the elemental and biochemical composition of non-target microalgal species. 1957 94


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