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Information on EC 1.7.1.3 - nitrate reductase (NADPH)
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1.7.1.3 nitrate reductase (NADPH)IUBMB Comments
An iron-sulfur molybdenum flavoprotein.
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Word Map
- 1.7.1.3
- neurospora
- crassa
- nidulans
- molybdenum
-
molybdenum-containing
-
nadph-cytochrome
- molybdopterin
-
positive-acting
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pathway-specific
-
viologen-nitrate
-
reductase-deficient
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nitrogen-related
- tungstate
-
nadh:nitrate
- synthesis
- analysis
- medicine
The enzyme appears in viruses and cellular organisms
Synonyms
nit-3, nadph-nitrate reductase, nadph-dependent nitrate reductase, nadph:nr, nadph:nitrate reductase, nitrate reductase (nadph), assimilatory nadph-nitrate reductase, 
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SYNONYM 
ORGANISM
UNIPROT
COMMENTARY 
LITERATURE
assimilatory NADPH-nitrate reductase
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Assimilatory nitrate reductase
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assimilatory reduced nicotinamide adenine dinucleotide phosphate-nitrate reductase
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EC 1.6.6.3
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formerly
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EC 1.7.99.4
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formerly, part transferred
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MSMEG_2837
NADPH-dependent nitrate reductase
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NADPH-nitrate reductase
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NADPH2:nitrate oxidoreductase
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NADPH:nitrate reductase
narB
nitrate reductase
nitrate reductase (NADPH)
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nitrate reductase (reduced nicotinamide adenine dinucleotide phosphate)
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triphosphopyridine nucleotide-nitrate reductase
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NADPH:nitrate reductase
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REACTION
REACTION DIAGRAM
COMMENTARY
ORGANISM
UNIPROT
LITERATURE
nitrite + NADP+ + H2O = nitrate + NADPH + H+
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nitrite + NADP+ + H2O = nitrate + NADPH + H+
An iron-sulfur molybdenum flavoprotein
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nitrite + NADP+ + H2O = nitrate + NADPH + H+
multicenter redox enzyme. Ser920, Arg921 and Arg932 are suggested to be the key enzymes to investigate for a role in determining pyridine nucleotide specificity. Arg932 may be playing a role in binding the adenine ring of NADPH
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nitrite + NADP+ + H2O = nitrate + NADPH + H+
random order rapid-equilibrium mechanism, two functional parts: 1. heat labile, FAD and haemoprotein containing, binds NADPH and transfers electrons from NADPH via FAD and perhaps cytochrome b to acceptors such as cytochrome c, 2. heat stable, molybdenum containing, accepts electrons from reduced viologen dyes and transfers them to nitrate
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nitrite + NADP+ + H2O = nitrate + NADPH + H+
sulfhydryl groups may participate in the binding of the protein subunits
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REACTION TYPE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
oxidation
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redox reaction
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reduction
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PATHWAY SOURCE
PATHWAYS
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SYSTEMATIC NAME
IUBMB Comments
nitrite:NADP+ oxidoreductase
An iron-sulfur molybdenum flavoprotein.
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CAS REGISTRY NUMBER
COMMENTARY
9029-28-1
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SUBSTRATE
PRODUCT
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate)
(Substrate)
LITERATURE
(Substrate)
(Substrate)
COMMENTARY
(Product)
(Product)
LITERATURE
(Product)
(Product)
Reversibility
r=reversible
ir=irreversible
?=not specified
r=reversible
ir=irreversible
?=not specified
chlorate + NADPH
chlorite + NADP+
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lower affinity than to nitrate, appears to be toxic or its product
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?
ferricytochrome c + NADPH + H+
ferrocytochrome c + NADP+ + H2O
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-
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r
nitrate + reduced anthraquinone 2-sulfonate
nitrite + anthraquinone 2-sulfonate
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-
?
NAD(P)H + H+ + nitrate
NAD(P)+ + nitrite + H2O
A0A8D3X5C3; A0A8D3X5J3
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-
-
?
NAD(P)H + H+ + nitrate
NAD(P)+ + nitrite + H2O
A0A8D3X5C3; A0A8D3X5J3
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?
nitrate + NADPH
nitrite + NADP+
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enzyme is essential for reduction of nitrate to ammonia, under oxic conditions the enzyme is involved in nitrate assimilation, under anoxic conditions the enzyme is used for dissimilatory nitrate reduction, transcription regulation mechanism via ammonium, nitrate, and O2 concentrations, overview
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-
?
nitrate + NADPH
nitrite + NADP+
enzyme is involved in nitrate assimilation
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?
nitrate + NADPH
nitrite + NADP+
enzyme is involved in nitrate assimilation, it serves the nitrogen nutrition of the host plant of Tuber borchii in symbiosis
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-
?
nitrate + NADPH
nitrite + NADP+
enzyme is involved in nitrate assimilation, it serves the nitrogen nutrition of the host plant of Tuber borchii in symbiosis
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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some mutants use hypoxanthine as nitrogen source, 4.5-S cytochrome-c reductase activity
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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4 activities: NADPH-nitrate reductase, FADH-nitrate reductase, reduced methyl viologen-nitrate reductase and NADPH-cytochrome c reductase
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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two associated activities: cytochrome c reductase and reduced viologen dye:nitrate reductase
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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catalyzes the NADPH-linked reduction of ferricyanide and 2,6-dichlorophenolindophenol, chlorate- and bromate-dependent NADPH oxidation, and FMNH-linked nitrate reduction
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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some mutants use hypoxanthine as nitrogen source, 4.5-S cytochrome-c reductase activity
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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associated cytochrome c reductase activity
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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key enzyme in the assimilation path of nitrate to ammonium. Crude extracts possess endogenous NADPH regenerating systems capable of providing reducing equivalents for effective nitrate reduction in vitro
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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20-fold higher activity with NADPH than with NADH
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ir
nitrate + NADPH
nitrite + NADP+ + H2O
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4 activities: NADPH-nitrate reductase, FADH-nitrate reductase, reduced methyl viologen-nitrate reductase and NADPH-cytochrome c reductase
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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4 activities: NADPH-nitrate reductase, FADH-nitrate reductase, reduced methyl viologen-nitrate reductase and NADPH-cytochrome c reductase
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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4 activities: NADPH-nitrate reductase, FADH-nitrate reductase, reduced methyl viologen-nitrate reductase and NADPH-cytochrome c reductase
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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associated FAD-nitrate reductase and methylviologen-nitrate activity
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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first step in nitrate assimilation
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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key enzyme in the assimilation path of nitrate to ammonium. Crude extracts possess endogenous NADPH regenerating systems capable of providing reducing equivalents for effective nitrate reduction in vitro
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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first step in the reduction of nitrate to ammonia, biosynthesis of amino acids and other nitrogen-containing cell constituents
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?
nitrate + NADPH
nitrite + NADP+ + H2O
-
20-fold higher activity with NADPH than with NADH
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ir
nitrate + NADPH
nitrite + NADP+ + H2O
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4 activities: NADPH-nitrate reductase, FADH-nitrate reductase, reduced methyl viologen-nitrate reductase and NADPH-cytochrome c reductase
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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first step in the reduction of nitrate to ammonia, biosynthesis of amino acids and other nitrogen-containing cell constituents
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?
nitrate + reduced methyl viologen
nitrite + oxidized methyl viologen
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?
nitrate + reduced methyl viologen
nitrite + oxidized methyl viologen
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?
reduced methyl viologen + nitrate
oxidized methyl viologen + nitrite + H2O
A0A8D3X5C3; A0A8D3X5J3
the optimum electron donor is methyl viologen plus Na2S2O4
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?
reduced methyl viologen + nitrate
oxidized methyl viologen + nitrite + H2O
A0A8D3X5C3; A0A8D3X5J3
the optimum electron donor is methyl viologen plus Na2S2O4
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?
additional information
?
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enzyme expression is regulated by different inorganic and organic nitrogen sources, e.g. nitrate, ammonium, urea and glutamate, regulatory mechanism of nitrate aquisition in ectomycchorizae, overview
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?
additional information
?
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NADPH-dependent cytochrome c reducing activity by the holo-enzyme is determined with FAD and NADPH spectroscopically at 550 nm and 340 nm. Apo-nitrate reductase has a marginally lower, about 10% reduced cytochrome c reducing activity, which correlates to its 15% reduced heme content
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?
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NATURAL SUBSTRATE
NATURAL PRODUCT
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate)
(Substrate)
LITERATURE
(Substrate)
(Substrate)
COMMENTARY
(Product)
(Product)
LITERATURE
(Product)
(Product)
REVERSIBILITY
r=reversible
ir=irreversible
?=not specified
r=reversible
ir=irreversible
?=not specified
additional information
?
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enzyme expression is regulated by different inorganic and organic nitrogen sources, e.g. nitrate, ammonium, urea and glutamate, regulatory mechanism of nitrate aquisition in ectomycchorizae, overview
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-
?
nitrate + NADPH
nitrite + NADP+
-
enzyme is essential for reduction of nitrate to ammonia, under oxic conditions the enzyme is involved in nitrate assimilation, under anoxic conditions the enzyme is used for dissimilatory nitrate reduction, transcription regulation mechanism via ammonium, nitrate, and O2 concentrations, overview
-
-
?
nitrate + NADPH
nitrite + NADP+
enzyme is involved in nitrate assimilation
-
-
?
nitrate + NADPH
nitrite + NADP+
enzyme is involved in nitrate assimilation, it serves the nitrogen nutrition of the host plant of Tuber borchii in symbiosis
-
-
?
nitrate + NADPH
nitrite + NADP+
enzyme is involved in nitrate assimilation, it serves the nitrogen nutrition of the host plant of Tuber borchii in symbiosis
-
-
?
nitrate + NADPH
nitrite + NADP+ + H2O
-
key enzyme in the assimilation path of nitrate to ammonium. Crude extracts possess endogenous NADPH regenerating systems capable of providing reducing equivalents for effective nitrate reduction in vitro
-
?
nitrate + NADPH
nitrite + NADP+ + H2O
-
first step in nitrate assimilation
-
?
nitrate + NADPH
nitrite + NADP+ + H2O
-
key enzyme in the assimilation path of nitrate to ammonium. Crude extracts possess endogenous NADPH regenerating systems capable of providing reducing equivalents for effective nitrate reduction in vitro
-
?
nitrate + NADPH
nitrite + NADP+ + H2O
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first step in the reduction of nitrate to ammonia, biosynthesis of amino acids and other nitrogen-containing cell constituents
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?
nitrate + NADPH
nitrite + NADP+ + H2O
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first step in the reduction of nitrate to ammonia, biosynthesis of amino acids and other nitrogen-containing cell constituents
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?
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COFACTOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
molybdopterin
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i.e Moco/MPT, binding of molybdenum cofactor to apo-nitrate reductase is independent from other prosthetic groups, molybdenum cofactor-dependent enzyme maturation, overview. Reconstitution of Moco-free nitrate reductase with various amounts of purified Moco carrier protein
cytochrome b557
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involved in intracellular electron transport from NADPH to nitrate
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FAD
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contains 5.91-7.78 nmol FAD per mg of protein, activation of NADPH-nitrate reductase activity
FAD
involved in electron transfer from NADPH to the enzyme molybdenum center where reduction of nitrate to nitrite takes place
heme
involved in electron transfer from NADPH to the enzyme molybdenum center where reduction of nitrate to nitrite takes place
molybdenum cofactor
cofactor is necessary and sufficient to induce dimer formation. The molybdenum center of nitrate reductase reconstituted in vitro from apo-enzyme and cofactor shows an EPR spectrum identical to holo-enzyme. Insertion of this cofactor into the enzyme occurs independent from the insertion of any other NR redox cofactor
molybdenum cofactor
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i.e Moco/MPT, binding of molybdenum cofactor to apo-nitrate reductase is independent from other prosthetic groups, molybdenum cofactor-dependent enzyme maturation, overview. Reconstitution of Moco-free nitrate reductase with various amounts of purified Moco carrier protein
additional information
enzyme amino acid sequence contains a molybdate-cofactor, a cytochrome b5 heme, and a FAD binding domain
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METALS and IONS
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
Fe
Fe2+
Molybdenum
NH4+
-
represses the intracellular NO3- assimilation, which is required for the induction and maintenace of NADPH nitrate reductase, enzyme is regulated by NH4+ at the transcriptional level
additional information
A0A8D3X5C3; A0A8D3X5J3
not inhibitory nor activating: Ba2+, Zn2+, EDTA
Molybdenum
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1 mol per mol enzyme protein, activation of enzyme after urea treatment, little stimulation
Molybdenum
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a functional nitrate reductase can be generated that lacks both the FAD and heme cofactors leaving the Mo active site as the sole redox active centre
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INHIBITOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
NADP+
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inhibits NADPH oxidation, non-competitive with respect to nitrate
nitrite
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competitive with respect to nitrate and non-competitive to NADPH
Phenylglyoxal
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in 0.1 M phosphate, pH 7.3, 4 mM, inactivation after 15 min to 40% and to 20% after 60 min
p-chloromercuribenzoate
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reversion of the inhibition by addition of reduced glutathione
additional information
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cysteine or dithiothreitol relieve or prevent inhibition. Not inhibited by urea, glutamic acid, aspartic acid and ammonia at 10 mM
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additional information
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exogenous ammonium represses enzyme expression under oxic conditions in presence or absence of nitrate, while under anoxic conditions the enzyme is expressed even in the presence of ammonium, promotor activity study
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additional information
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intracellularly accumulated nitrite can inhibit nitrate uptake, addition of nitrite at concentrations above 5 mM is toxic and causes growth retardation
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additional information
the nitrogen sources nitrate, glutamate, and urea induce enzyme expression, but ammonium represses it
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additional information
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protection of inactivation by FAD and restorage by dithiothreitol
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additional information
A0A8D3X5C3; A0A8D3X5J3
not inhibitory nor activating: Ba2+, Zn2+, EDTA
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ACTIVATING COMPOUND
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
FAD
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activates 10fold by addition of 0.004 mM, stabilizes against heat inactivation
additional information
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exogenous nitrate induces the enzyme expression, can be repressed by ammonium under aerobic conditions, but not under anaerobic conditions, promotor activity study
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additional information
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growth stimulation is higher on nitrate than on nitrite
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additional information
the nitrogen sources nitrate, glutamate, and urea induce enzyme expression, but ammonium represses it
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additional information
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enzyme can be reactivated by molybdenum and dithioerythritol
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KM VALUE [mM]
SUBSTRATE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
3
FMNH2