Nitrate Assimilation: Nitrate and Nitrite Reductases

Ipomoea cells grown in a medium containing ammonium and nitrate preferentially used ammonium during the initial stages of growth but in the later stages assimilated nitrate rapidly regardless of the presence or absence of ammonium. Cells grown on nitrate and maintained at pH 4.8 released ammonia into the medium, whereas when they were maintained at pH 6.5 they secreted nitrite. The enzymes of nitrate assimilation were inducible by nitrate and the activities changed considerably in response to nitrogen source. The addition of ammonium 3 days after inoculation to cells highly induced for the reductases did not result in the suppression of further synthesis of the enzymes. The levels of nitrate (EC 1.6.6.1) and nitrite (EC 1.6.6.4) reductases detected in cells grown on ammonium as the nitrogen source were about 25% and 66%, respectively, of the fully induced level. The addition of nitrate to ammonium-assimilating cells resulted in a low level of induction of both reductases. Addition of nitrite had no effect. With both ammonium and nitrate initially present in the medium, the ammonium was utilized quickly but no induction of the reductases was observed for 24 h. the time interval when the assimilation of nitrate was low. This was followed by the induction of the enzymes to a higher level than the activity in cultures of similar age that had been grown continually in nitrate, supplied at the same concentration. Thus, for nitrate and nitrite reductases, repression-like effects were produced by ammonium.

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Induction of the Nitrate AssimilationnirAOperon and Protein-Protein Interactions in the Maturation of Nitrate and Nitrite Reductases in the Cyanobacterium Anabaena sp. Strain PCC 7120

Journal of Bacteriology ◽

10.1128/jb.00198-15 ◽

2015 ◽

Vol 197 (14) ◽

pp. 2442-2452 ◽

Cited By ~ 8

Author(s):

José E. Frías ◽

Enrique Flores

Keyword(s):

Nitrate Reductase ◽

Protein Interactions ◽

Nitrite Reductase ◽

Nitrate Assimilation ◽

Protein Protein Interactions ◽

Content Type ◽

Nitrite Reductases ◽

Nitrate And Nitrite ◽

Pcc 7120 ◽

Assimilation System

ABSTRACTNitrate is widely used as a nitrogen source by cyanobacteria, in which the nitrate assimilation structural genes frequently constitute the so-callednirAoperon. This operon contains the genes encoding nitrite reductase (nirA), a nitrate/nitrite transporter (frequently an ABC-type transporter;nrtABCD), and nitrate reductase (narB). In the model filamentous cyanobacteriumAnabaenasp. strain PCC 7120, which can fix N2in specialized cells termed heterocysts, thenirAoperon is expressed at high levels only in media containing nitrate or nitrite and lacking ammonium, a preferred nitrogen source. Here we examined the genes downstream of thenirAoperon inAnabaenaand found that a small open reading frame of unknown function,alr0613, can be cotranscribed with the operon. The next gene in the genome,alr0614(narM), showed an expression pattern similar to that of thenirAoperon, implying correlated expression ofnarMand the operon. A mutant ofnarMwith an insertion mutation failed to produce nitrate reductase activity, consistent with the idea that NarM is required for the maturation of NarB. BothnarMandnarBmutants were impaired in the nitrate-dependent induction of thenirAoperon, suggesting that nitrite is an inducer of the operon inAnabaena. It has previously been shown that the nitrite reductase protein NirA requires NirB, a protein likely involved in protein-protein interactions, to attain maximum activity. Bacterial two-hybrid analysis confirmed possible NirA-NirB and NarB-NarM interactions, suggesting that the development of both nitrite reductase and nitrate reductase activities in cyanobacteria involves physical interaction of the corresponding enzymes with their cognate partners, NirB and NarM, respectively.IMPORTANCENitrate is an important source of nitrogen for many microorganisms that is utilized through the nitrate assimilation system, which includes nitrate/nitrite membrane transporters and the nitrate and nitrite reductases. Many cyanobacteria assimilate nitrate, but regulation of the nitrate assimilation system varies in different cyanobacterial groups. In the N2-fixing, heterocyst-forming cyanobacteria, thenirAoperon, which includes the structural genes for the nitrate assimilation system, is expressed in the presence of nitrate or nitrite if ammonium is not available to the cells. Here we studied the genes required for production of an active nitrate reductase, providing information on the nitrate-dependent induction of the operon, and found evidence for possible protein-protein interactions in the maturation of nitrate reductase and nitrite reductase.

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Primary nitrogen assimilation in higher plants and its regulation

Canadian Journal of Botany ◽

10.1139/b94-094 ◽

1994 ◽

Vol 72 (6) ◽

pp. 739-750 ◽

Cited By ~ 117

Author(s):

Ann Oaks

Keyword(s):

Nitrogen Assimilation ◽

Higher Plants ◽

Nitrate Assimilation ◽

Glutamate Synthase ◽

Ammonium Assimilation ◽

Cellular Organization ◽

Nitrite Reductases ◽

Leaf Tissues ◽

Nitrate And Nitrite ◽

Key Words Nitrate

Characteristics of the enzymes involved in the assimilation of NO3− and NH4+, in particular the nitrate and nitrite reductases, glutamine synthetase, glutamate synthase, glutamate dehydrogenase, glutamate decarboxylase, and asparagine synthetase, are described. The cellular organization of these enzymes in root and leaf tissues are assessed in view of recent research developments that utilize various tissue blotting techniques. Regulation of nitrate assimilation is analyzed at the physiological, biochemical, and molecular levels. Key words: nitrate, ammonium, assimilation, regulation.

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Light-Independent Nitrogen Assimilation in Plant Leaves: Nitrate Incorporation into Glutamine, Glutamate, Aspartate, and Asparagine Traced by 15N

Plants ◽

10.3390/plants9101303 ◽

2020 ◽

Vol 9 (10) ◽

pp. 1303

Author(s):

Tadakatsu Yoneyama ◽

Akira Suzuki

Keyword(s):

Amino Acids ◽

Nitrogen Assimilation ◽

Nitrate Assimilation ◽

Glutamate Synthase ◽

Enzymatic Reactions ◽

Nitrite Reductases ◽

Leaf Tissues ◽

Nitrate And Nitrite ◽

Cellular Compartments ◽

Donor System

Although the nitrate assimilation into amino acids in photosynthetic leaf tissues is active under the light, the studies during 1950s and 1970s in the dark nitrate assimilation provided fragmental and variable activities, and the mechanism of reductant supply to nitrate assimilation in darkness remained unclear. 15N tracing experiments unraveled the assimilatory mechanism of nitrogen from nitrate into amino acids in the light and in darkness by the reactions of nitrate and nitrite reductases, glutamine synthetase, glutamate synthase, aspartate aminotransferase, and asparagine synthetase. Nitrogen assimilation in illuminated leaves and non-photosynthetic roots occurs either in the redundant way or in the specific manner regarding the isoforms of nitrogen assimilatory enzymes in their cellular compartments. The electron supplying systems necessary to the enzymatic reactions share in part a similar electron donor system at the expense of carbohydrates in both leaves and roots, but also distinct reducing systems regarding the reactions of Fd-nitrite reductase and Fd-glutamate synthase in the photosynthetic and non-photosynthetic organs.

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Nitrate Respiration in Thermus thermophilus NAR1: from Horizontal Gene Transfer to Internal Evolution

Genes ◽

10.3390/genes11111308 ◽

2020 ◽

Vol 11 (11) ◽

pp. 1308

Author(s):

Mercedes Sánchez-Costa ◽

Alba Blesa ◽

José Berenguer

Keyword(s):

Gene Transfer ◽

Horizontal Gene Transfer ◽

Nadh Dehydrogenase ◽

Thermus Thermophilus ◽

Nitrate Respiration ◽

Small Plasmid ◽

Nitrite Reductases ◽

Nitrite Respiration ◽

Nitrate And Nitrite ◽

Internal Evolution

Genes coding for enzymes of the denitrification pathway appear randomly distributed among isolates of the ancestral genus Thermus, but only in few strains of the species Thermus thermophilus has the pathway been studied to a certain detail. Here, we review the enzymes involved in this pathway present in T. thermophilus NAR1, a strain extensively employed as a model for nitrate respiration, in the light of its full sequence recently assembled through a combination of PacBio and Illumina technologies in order to counteract the systematic errors introduced by the former technique. The genome of this strain is divided in four replicons, a chromosome of 2,021,843 bp, two megaplasmids of 370,865 and 77,135 bp and a small plasmid of 9799 pb. Nitrate respiration is encoded in the largest megaplasmid, pTTHNP4, within a region that includes operons for O2 and nitrate sensory systems, a nitrate reductase, nitrate and nitrite transporters and a nitrate specific NADH dehydrogenase, in addition to multiple insertion sequences (IS), suggesting its mobility-prone nature. Despite nitrite is the final product of nitrate respiration in this strain, the megaplasmid encodes two putative nitrite reductases of the cd1 and Cu-containing types, apparently inactivated by IS. No nitric oxide reductase genes have been found within this region, although the NorR sensory gene, needed for its expression, is found near the inactive nitrite respiration system. These data clearly support that partial denitrification in this strain is the consequence of recent deletions and IS insertions in genes involved in nitrite respiration. Based on these data, the capability of this strain to transfer or acquire denitrification clusters by horizontal gene transfer is discussed.

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