This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: nitrate assimilation
|Superclasses:||Degradation/Utilization/Assimilation → Inorganic Nutrients Metabolism → Nitrogen Compounds Metabolism → Nitrate Reduction|
Some taxa known to possess this pathway include : Arabidopsis thaliana col
In plants and algae nitrate is an important source of nitrogen. Nitrate assimilation begins with the uptake of nitrate from the soil by the root. Root epidermal and cortical cells are the first to actively transport nitrate into their cytosols. Nitrate then crosses the endodermis of the root and is released into the xylem. After long distance transport up the xylem, nitrate is again actively transported into the cells of the leaf. Once in the cell, nitrate can be stored in the vacuole (due to toxicity) or reduced to nitrite by the enzyme nitrate reductase (NR).
Four classes of nitrate reductases are known - a eukaryotic class, and three prokaryotic classes. The eukaryotic nitrate reductases are found in plants, algae and fungi, and are involved in assimilation of nitrate. They are composed of two identical subunits, and contain a MoO2-molybdopterin cofactor and an FAD prosthetic group. In general, plant enzymes prefer NADH as the electron donor ( E.C. 126.96.36.199) and fungal enzymes prefer NADPH ( E.C. 188.8.131.52), although some enzymes were reported to accept either of these compounds ( E.C. 184.108.40.206) [Beevers64]. Example for eukaryotic enzymes include the assimilatory nitrate reductase (NADH) from Arabidopsis thaliana and the assimilatory nitrate reductase (NADPH) from Neurospora crassa.
Nitrite is transported into the chloroplast, where it is reduced to ammonia by nitrite reductase (NiR). The final step of the pathway is the incorporation of ammonia into glutamine by glutamine synthetase [Elliot94].
Variants: nitrate reduction I (denitrification), nitrate reduction III (dissimilatory), nitrate reduction IV (dissimilatory), nitrate reduction V (assimilatory), nitrate reduction VI (assimilatory), nitrate reduction VII (denitrification), nitrate reduction VIII (dissimilatory), nitrate reduction IX (dissimilatory), nitrate reduction X (periplasmic, dissimilatory)
Beevers64: Beevers, L, Flesher, D., Hageman, R.H. (1964). "Studies on the pyridine nucleotide specificity of nitrate reductase in higher plants and its relationship to sulfhydryl level." Biochim Biophys Acta 89:453-64. PMID: 14209328
Alibhai94: Alibhai M, Villafranca JJ (1994). "Kinetic and mutagenic studies of the role of the active site residues Asp-50 and Glu-327 of Escherichia coli glutamine synthetase." Biochemistry 33(3);682-6. PMID: 7904829
Amaya05: Amaya KR, Kocherginskaya SA, Mackie RI, Cann IK (2005). "Biochemical and mutational analysis of glutamine synthetase type III from the rumen anaerobe Ruminococcus albus 8." J Bacteriol 187(21);7481-91. PMID: 16237031
Balakrishnan78: Balakrishnan MS, Villafranca JJ (1978). "Distance determinations between the metal ion sites of Escherichia coli glutamine synthetase by electron paramagnetic resonance using Cr(III)--nucleotides as paramagnetic substrate analogues." Biochemistry 17(17);3531-8. PMID: 28753
Bender77: Bender RA, Janssen KA, Resnick AD, Blumenberg M, Foor F, Magasanik B (1977). "Biochemical parameters of glutamine synthetase from Klebsiella aerogenes." J Bacteriol 129(2);1001-9. PMID: 14104
CohenKupiec93: Cohen-Kupiec R, Gurevitz M, Zilberstein A (1993). "Expression of glnA in the cyanobacterium Synechococcus sp. strain PCC 7942 is initiated from a single nif-like promoter under various nitrogen conditions." J Bacteriol 175(23);7727-31. PMID: 7902350
Crawford88: Crawford NM, Smith M, Bellissimo D, Davis RW (1988). "Sequence and nitrate regulation of the Arabidopsis thaliana mRNA encoding nitrate reductase, a metalloflavoprotein with three functional domains." Proc Natl Acad Sci U S A 1988;85(14);5006-10. PMID: 3393528
Dahlquist75: Dahlquist FW, Purich DL (1975). "Regulation of Escherichia coli glutamine synthetase. Evidence for the action of some feedback modifiers at the active site of the unadenylylated enzyme." Biochemistry 14(9);1980-9. PMID: 235974
Dhalla94: Dhalla AM, Li B, Alibhai MF, Yost KJ, Hemmingsen JM, Atkins WM, Schineller J, Villafranca JJ (1994). "Regeneration of catalytic activity of glutamine synthetase mutants by chemical activation: exploration of the role of arginines 339 and 359 in activity." Protein Sci 3(3);476-81. PMID: 7912599
Hofmann78: Hofmann GE, Glaunsinger WS (1978). "EPR investigation of the Mn(II) binding sites in glutamine synthetase (Escherichia coli W). I. High-affinity binding sites." J Biochem (Tokyo) 83(6);1769-78. PMID: 27502
Hofmann78a: Hofmann GE, Glaunsinger WS (1978). "EPR investigation of the Mn(II) binding sites in glutamine synthetase (Escherichia coli W). II. Intermediate-affinity binding sites." J Biochem (Tokyo) 83(6);1779-82. PMID: 27503
Ishiyama04: Ishiyama K, Inoue E, Watanabe-Takahashi A, Obara M, Yamaya T, Takahashi H (2004). "Kinetic properties and ammonium-dependent regulation of cytosolic isoenzymes of glutamine synthetase in Arabidopsis." J Biol Chem 279(16);16598-605. PMID: 14757761
Kingdon67: Kingdon HS, Stadtman ER (1967). "Regulation of glutamine synthetase. X. Effect of growth conditions on the susceptibility of Escherichia coli glutamine synthetase to feedback inhibition." J Bacteriol 94(4);949-57. PMID: 4860919
Listrom97: Listrom CD, Morizono H, Rajagopal BS, McCann MT, Tuchman M, Allewell NM (1997). "Expression, purification, and characterization of recombinant human glutamine synthetase." Biochem J 328 ( Pt 1);159-63. PMID: 9359847
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