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Information on EC 1.7.2.2 - nitrite reductase (cytochrome; ammonia-forming)
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1.7.2.2 nitrite reductase (cytochrome; ammonia-forming)IUBMB Comments
Found as a multiheme cytochrome in many bacteria. The enzyme from Escherichia coli contains five hemes c and requires Ca2+. It also reduces nitric oxide and hydroxylamine to ammonia, and sulfite to sulfide.
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Word Map
- 1.7.2.2
-
six-electron
- desulfovibrio
-
dissimilatory
- succinogenes
-
wolinella
- nitrosomonas
-
ammonification
- thioalkalivibrio
- nitratireducens
- desulfuricans
- chromatium
- flavorubredoxin
- deleyianum
- menaquinol
- hydrogenobacter
-
pentahaem
- hildenborough
- sulfurospirillum
- ferrocytochrome
- flavohemoglobins
-
cxxch
- analysis
The enzyme appears in viruses and cellular organisms
Synonyms
cytochrome c-552, cytochrome c nitrite reductase, ccnir, tvnir, nrfha, octahaem cytochrome c nitrite reductase, hexaheme c-type cytochrome, cytochrome c nitrite reductase complex, nrfa2nrfh complex, ammonia-forming cytochrome c nitrite reductase, 
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SYNONYM 
ORGANISM
UNIPROT
COMMENTARY 
LITERATURE
ccNiR
cytochrome c nitrite reductase
cytochrome c-552
epsilonHao
epsilonproteobacterial hydroxylamine oxidoreductase
Glov_1042
haoA
multihaem c NiR
multiheme nitrite reductase
-
-
-
-
NiR
nirB
NirC
NrfA
SCO2486
SCO2488
TvNiR
WS0969
additional information
cytochrome c nitrite reductase
-
-
-
-
NiR
Marinobacter nauticus 617
-
-
-
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REACTION
REACTION DIAGRAM
COMMENTARY
ORGANISM
UNIPROT
LITERATURE
NH3 + 2 H2O + 6 ferricytochrome c = nitrite + 6 ferrocytochrome c + 7 H+
-
-
-
-
NH3 + 2 H2O + 6 ferricytochrome c = nitrite + 6 ferrocytochrome c + 7 H+
reaction mechanism, overview. NO2- binds to the enzyme ccNIR catalytic heme in the Fe2+ state, accepts two protons, and releases H2O to form a moiety formally written as Fe(II)-[NO+]. The key mechanistic challenge in reducing NO2- is to avoid or overcome formation of the terminal Fe(II)-NO thermodynamic sink through one-electron reduction of Fe(II)-[NO+]. Enzyme ccNIR achieves this by two proton-coupled electron transfer reductions that promptly reduce Fe(II)-[NO+] to Fe(II)-[HNO]. The process involves recharging of the catalytic heme with electrons obtained through transfer from the other hemes of the enzyme and of the heme environment with protons
-
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REACTION TYPE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
oxidation
-
-
-
-
redox reaction
-
-
-
-
reduction
reduction
-
-
-
-
reduction
-
TvNiR catalyzes the reduction of nitrite and hydroxylamine to ammonium ions without the release of any intermediates.
reduction
-
TvNiR catalyzes the reduction of nitrite and hydroxylamine to ammonium ions without the release of any intermediates.
-
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PATHWAY SOURCE
PATHWAYS
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SYSTEMATIC NAME
IUBMB Comments
ammonia:ferricytochrome-c oxidoreductase
Found as a multiheme cytochrome in many bacteria. The enzyme from Escherichia coli contains five hemes c and requires Ca2+. It also reduces nitric oxide and hydroxylamine to ammonia, and sulfite to sulfide.
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CAS REGISTRY NUMBER
COMMENTARY
37256-41-0
-
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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
hydroxylammonium + ferrocytochrome c
NH3 + ferricytochrome c + H2O
-
-
-
-
?
nitrite + 4 ferrocytochrome c + 5 H+
hydroxylamine + H2O + 4 ferricytochrome c
-
cf. EC 1.7.2.6
-
-
?
nitrite + acceptor
NH3 + oxidized acceptor + H2O
Q5F2I3
-
-
-
?
nitrite + ferrocytochrome c + 6 H+
NH3 + ferricytochrome c + 2 H2O
-
-
-
-
?
nitrite + reduced + acceptor
NH3 + oxidized acceptor + H2O
-
-
-
?
nitrite + reduced anthraquinone-2-sulfonate + H+
NH3 + H2O + oxidized anthraquinone-2-sulfonate
about 95% conversion
-
-
?
nitrite + reduced diquat + H+
NH3 + H2O + oxidized diquat
100% conversion
-
-
?
nitrite + reduced indigo carmine + H+
NH3 + H2O + oxidized indigo carmine
75% conversion
-
-
?
nitrite + reduced methyl viologen + H+
NH3 + H2O + oxidized methyl viologen
about 98% conversion
-
-
?
nitrite + reduced phenosafranine + H+
NH3 + H2O + oxidized phenosafranine
about 102% conversion
-
-
?
sulfite + reduced methyl viologen
H2S + oxidized methyl viologen + H2O
Q5F2I3
-
-
-
?
sulfite + reduced methyl viologen + H+
H2S + oxidized methyl viologen + H2O
Q5F2I3
-
-
-
?
ammonia + H2O + oxidized cytochrome C552
nitrite + reduced cytochrome C552
Marinobacter nauticus
-
-
-
-
?
ammonia + H2O + oxidized cytochrome C552
nitrite + reduced cytochrome C552
Marinobacter nauticus 617
-
-
-
-
?
hydroxylamine + benzyl viologen reduced
? + benzyl viologen oxidized
-
-
-
?
hydroxylamine + benzyl viologen reduced
? + benzyl viologen oxidized
-
-
-
?
hydroxylamine + ferricytochrome c
nitrite + ferrocytochrome c
-
-
-
-
r
hydroxylamine + ferricytochrome c
nitrite + ferrocytochrome c
-
-
-
r
hydroxylamine + ferricytochrome c
nitrite + ferrocytochrome c
-
-
-
-
r
hydroxylamine + ferricytochrome c
nitrite + ferrocytochrome c
-
-
-
-
r
hydroxylamine + ferrocytochrome c
NH3 + ferricytochrome c + H2O
-
-
-
-
?
hydroxylamine + ferrocytochrome c
NH3 + ferricytochrome c + H2O
-
-
-
-
?
hydroxylamine + ferrocytochrome c
NH3 + ferricytochrome c + H2O
-
10 mM hydroxylamine
-
-
ir
hydroxylamine + ferrocytochrome c
NH3 + ferricytochrome c + H2O
-
-
-
-
?
hydroxylamine + ferrocytochrome c
NH3 + ferricytochrome c + H2O
-
10 mM hydroxylamine
-
-
ir
hydroxylamine + ferrocytochrome c
NH3 + H2O + ferricytochrome c
-
cf. EC 1.7.99.1
-
-
?
hydroxylamine + ferrocytochrome c
NH3 + H2O + ferricytochrome c
-
cf. EC 1.7.99.1
-
-
r
hydroxylamine + ferrocytochrome c
NH3 + H2O + ferricytochrome c
-
best substrate, cf. EC 1.7.99.1
-
-
r
hydroxylamine + ferrocytochrome c
NH3 + H2O + ferricytochrome c
cf. EC 1.7.99.1
-
-
r
hydroxylamine + ferrocytochrome c
NH3 + H2O + ferricytochrome c
-
cf. EC 1.7.99.1
-
-
r
hydroxylamine + ferrocytochrome c
NH3 + H2O + ferricytochrome c
-
cf. EC 1.7.99.1
-
-
r
hydroxylamine + ferrocytochrome c
NH3 + H2O + ferricytochrome c
-
best substrate, cf. EC 1.7.99.1
-
-
r
hydroxylamine + reduced benzyl viologen
? + oxidized benzyl viologen
-
-
-
?
hydroxylamine + reduced benzyl viologen
? + oxidized benzyl viologen
-
-
-
?
hydroxylamine + reduced benzyl viologen
? + oxidized benzyl viologen
-
-
-
?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
-
-
-
-
?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
-
very low activity
-
-
?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
-
-
-
?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
-
-
-
-
?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
-
best substrate
-
-
?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
-
-
-
-
?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
-
-
-
-
?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
Lacticaseibacillus casei LCR 6013
-
-
-
-
?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
-
-
-
-
?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
-
-
-
?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
-
-
-
-
?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
-
mechanism
-
-
?
nitrite + benzyl viologen reduced + H+
NH4+ + benzyl viologen oxidized + H2O
-
-
-
?
nitrite + benzyl viologen reduced + H+
NH4+ + benzyl viologen oxidized + H2O
-
-
-
?
nitrite + electron donor protein
NH3 + oxidized electron donor protein
-
-
-
-
?
nitrite + electron donor protein
NH3 + oxidized electron donor protein
Lacticaseibacillus casei LCR 6013
-
-
-
-
?
nitrite + ferrocytochrome c
NH3 + ferricytochrome c + H2O
-
-
-
-
?
nitrite + ferrocytochrome c
NH3 + ferricytochrome c + H2O
-
-
-
-
?
nitrite + ferrocytochrome c + H+
NH3 + H2O + ferricytochrome c
-
-
-
?
nitrite + ferrocytochrome c + H+
NH3 + H2O + ferricytochrome c
the periplasmic cytochrome c nitrite reductase, Nrf, system of Escherichia coli utilizes nitrite as a respiratory electron acceptor by reducing it to ammonium. NO is a proposed intermediate in this six-electron reduction and NrfA can use exogenous NO as a substrate
-
-
?
nitrite + ferrocytochrome c + H+
NH3 + H2O + ferricytochrome c
-
protection against NO may involve reductive detoxification in low-oxygen environments, and three enzymes, flavorubredoxin, flavohaemoglobin and cytochrome c nitrite reductase: Determination of a combined role for NorV and NrfA in NO detoxification under anaerobic conditions, overview
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-
?
nitrite + ferrocytochrome c + H+
NH3 + H2O + ferricytochrome c
-
-
-
?
nitrite + ferrocytochrome c + H+
NH3 + H2O + ferricytochrome c
ccNiR catalyzes the six-electron reduction of nitrite to ammonia as the final step in the dissimilatory pathway of nitrate ammonification
-
-
?
nitrite + ferrocytochrome c + H+
NH3 + H2O + ferricytochrome c
nitrite is the preferred substrate. ccNiR is encoded by gene nrfA performing nitrite reduction with formate. Sulfite and nitrite both provide a pair of electrons to form the coordinative bond to the Fe(III) active site of the enzyme
-
-
?
nitrite + reduced methyl viologen
NH3 + H2O + oxidized methyl viologen
-
nitrite and inhibitor CO both bind to the catalytic heme
-
-
?
nitrite + reduced methyl viologen
NH3 + H2O + oxidized methyl viologen
-
-
-
-
?
nitrite + reduced methyl viologen
NH3 + H2O + oxidized methyl viologen
-
-
-
?
nitrite + reduced methyl viologen
NH3 + H2O + oxidized methyl viologen
-
-
-
-
?
nitrite + reduced methyl viologen
NH3 + H2O + oxidized methyl viologen
-
-
-
?
nitrite + reduced methyl viologen
NH3 + H2O + oxidized methyl viologen
-
-
-
-
?
nitrite + reduced methyl viologen
NH3 + H2O + oxidized methyl viologen
Q5F2I3
-
-
-
?
nitrite + reduced methyl viologen
NH3 + H2O + oxidized methyl viologen
-
-
-
?
nitrite + reduced methyl viologen
NH3 + H2O + oxidized methyl viologen
-
-
-
?
nitrite + reduced methyl viologen
NH3 + oxidized methyl viologen + H2O
-
-
-
-
?
nitrite + reduced methyl viologen
NH3 + oxidized methyl viologen + H2O
Q5F2I3
-
-
-
?
nitrite + reduced methyl viologen
NH3 + oxidized methyl viologen + H2O
Trichlorobacter lovleyi
-
-
-
?
nitrite + reduced methyl viologen
NH3 + oxidized methyl viologen + H2O
Trichlorobacter lovleyi DSM 17278
-
-
-
?
NO + 5 ferrocytochrome c + 5 H+
NH3 + H2O + 5 ferricytochrome c
-
important role for the enzyme in nitric oxide management in oxygen-limited environments. Nitric oxide is a key element in host defense against invasive pathogens
-
-
?
NO + 5 ferrocytochrome c + 5 H+
NH3 + H2O + 5 ferricytochrome c
-
-
-
-
?
sulfite + 6 ferrocytochrome c + 6 H+
H2S + 3 H2O + 6 ferricytochrome c
-
-
-
?
sulfite + 6 ferrocytochrome c + 6 H+
H2S + 3 H2O + 6 ferricytochrome c
sulfite and nitrite both provide a pair of electrons to form the coordinative bond to the Fe(III) active site of the enzyme, and the oxygen atoms of sulfite are found to interact with the three active site protein residues conserved within the enzyme family, binding mode of sulfite to the catalytic heme center of ccNiR, overview
-
-
?
additional information
?
-
-
the recombinant enzyme is able to catalyze reduction of nitrite (yielding ammonium) and hydroxylamine, EC 1.7.99.1, whereas hydroxylamine oxidation is negligible
-
-
?
additional information
?
-
the recombinant enzyme is able to catalyze reduction of nitrite (yielding ammonium) and hydroxylamine, EC 1.7.99.1, whereas hydroxylamine oxidation is negligible
-
-
?
additional information
?
-
-
the recombinant enzyme is able to catalyze reduction of nitrite (yielding ammonium) and hydroxylamine, EC 1.7.99.1, whereas hydroxylamine oxidation is negligible
-
-
?
additional information
?
-
-
the recombinant enzyme is able to catalyze reduction of nitrite (yielding ammonium) and hydroxylamine, EC 1.7.99.1, whereas hydroxylamine oxidation is negligible
-
-
?
additional information
?
-
-
active site structure determination and analysis, proton transfer is coupled to electron transfer at the active site, overview
-
-
?
additional information
?
-
-
NrfA from Escherichia coli has a well established role in the respiratory reduction of nitrite to ammonium, it might also participate in NO radical detoxification, detoxifying exogenously generated NO radical encountered during invasion of a human host, overview
-
-
?
additional information
?
-
-
the enzyme shows a common site for reduction of all three substrates as axial ligands to the lysine-coordinated NrfA heme rather than nonspecific NO radical reduction at one of the four His-His coordinated hemes also present in each NrfA subunit. NO radical reduction is initiated at similar potentials to NrfA-catalyzed reduction of nitrite and hydroxylamine
-
-
?
additional information
?
-
the NrfA active site consists of a hexacoordinate high-spin heme with a lysine ligand on the proximal side and water/hydroxide or substrate on the distal side. There are four further highly conserved active site residues including a Q263 positioned near the heme iron for which the side chain, unusually, coordinates a conserved, essential calcium ion, overview. Important function of the Q263-calcium ion pair increasing substrate affinity through its role in supporting a network of hydrogen bonded water molecules stabilizing the active site heme distal ligand, active site structures of native and Q263 mutant NrfA enzymes, overview
-
-
?
additional information
?
-
-
the NrfA active site consists of a hexacoordinate high-spin heme with a lysine ligand on the proximal side and water/hydroxide or substrate on the distal side. There are four further highly conserved active site residues including a Q263 positioned near the heme iron for which the side chain, unusually, coordinates a conserved, essential calcium ion, overview. Important function of the Q263-calcium ion pair increasing substrate affinity through its role in supporting a network of hydrogen bonded water molecules stabilizing the active site heme distal ligand, active site structures of native and Q263 mutant NrfA enzymes, overview
-
-
?
additional information
?
-
-
no nitrate or sulfite reductase activity
-
-
?
additional information
?
-
-
not accepted electron donors: NADH, NADPH, ubiquinol-1, menadiol, formate, D-lactate, sn-glycerol-3-phosphate
-
-
?
additional information
?
-
-
no nitrate or sulfite reductase activity
-
-
?
additional information
?
-
-
not accepted electron donors: NADH, NADPH, ubiquinol-1, menadiol, formate, D-lactate, sn-glycerol-3-phosphate
-
-
?
additional information
?
-
-
electron domor protein from strain Lactobacillus casei LCR 6013 and cytochrome c are the most effecitive for nitrite degradation
-
-
-
additional information
?
-
Lacticaseibacillus casei LCR 6013
-
electron domor protein from strain Lactobacillus casei LCR 6013 and cytochrome c are the most effecitive for nitrite degradation
-
-
-
additional information
?
-
-
the recombinant enzyme is able to catalyze reduction of nitrite (yielding ammonium) and hydroxylamine, EC 1.7.99.1, whereas hydroxylamine oxidation is negligible
-
-
?
additional information
?
-
protein film voltammetry shows that all detected electron transfer steps are one-electron in nature. Enzyme displays substrate inhibition during nitrite turnover and negative cooperativity during hydroxylamine turnover
-
-
?
additional information
?
-
-
protein film voltammetry shows that all detected electron transfer steps are one-electron in nature. Enzyme displays substrate inhibition during nitrite turnover and negative cooperativity during hydroxylamine turnover
-
-
?
additional information
?
-
enzyme catalyzes the six-electron reduction of nitrite to ammonia in vivo, but oxidizes hydroxylamine in the presence of large quantities of this substrate, yielding nitrite as the sole free nitrogenous product, reaction of EC 1.7.2.6
-
-
?
additional information
?
-
-
enzyme catalyzes the six-electron reduction of nitrite to ammonia in vivo, but oxidizes hydroxylamine in the presence of large quantities of this substrate, yielding nitrite as the sole free nitrogenous product, reaction of EC 1.7.2.6
-
-
?
additional information
?
-
-
no reaction with chloride, bromate and nitrate
-
-
?
additional information
?
-
-
the enzyme possesses also peroxidase activity
-
-
?
additional information
?
-
-
no reaction with chloride, bromate and nitrate
-
-
?
additional information
?
-
-
the enzyme possesses also peroxidase activity
-
-
?
additional information
?
-
-
the enzyme catalyzes the last step in the metabolic pathway of nitrate dissimilation
-
-
?
additional information
?
-
ccNiR also reduces sulfite to sulfide linking the biogeochemical cycles of nitrogen and of sulfur
-
-
?
additional information
?
-
-
ccNiR also reduces sulfite to sulfide linking the biogeochemical cycles of nitrogen and of sulfur
-
-
?
additional information
?
-
simulation of the kinetics of the reduction process reveals that the complex recharging process can be accomplished in two possible ways: either through two consecutive proton-coupled electron transfers or in the form of three consecutive elementary steps involving reduction, proton-coupled electron transfers and protonation. Recharging through two proton-coupled electron transfers is a means of overcoming the predicted deep energetic minimum that is calculated to occur at the stage of the Fe(II)-NO radical intermediate. The radical transfer role for the active-site Tyr218, cannot be confirmed. The highly conserved calcium located in the direct proximity of the active site plays an important role in the substrate conversion through the facilitation of the proton transfer steps
-
-
?
additional information
?
-
the first event in the second halfcycle is the reduction of the HNO intermediate, which is accomplished by two proton-coupled electron transfer reactions. Two isomeric radical intermediates, HNOH radial and H2NO radical, are formed. Both intermediates are readily transformed into hydroxylamine, most likely through intramolecular proton transfer from either Arg114 or His277. An extra proton must enter the active site of the enzyme to initiate heterolytic cleavage of the N-O bond. As a result of N-O bond cleavage, the H2N+ intermediate is formed. It picks up an electron, forming H2N+ radical, which in turn reacts with Tyr218. The intramolecular reaction with Tyr218 in the final step of the nitrite reduction process leads directly to the final product, ammonia. Dissociation of the final product proceeds concomitantly with a change in spin state
-
-
?
additional information
?
-
simulation of the kinetics of the reduction process reveals that the complex recharging process can be accomplished in two possible ways: either through two consecutive proton-coupled electron transfers or in the form of three consecutive elementary steps involving reduction, proton-coupled electron transfers and protonation. Recharging through two proton-coupled electron transfers is a means of overcoming the predicted deep energetic minimum that is calculated to occur at the stage of the Fe(II)-NO radical intermediate. The radical transfer role for the active-site Tyr218, cannot be confirmed. The highly conserved calcium located in the direct proximity of the active site plays an important role in the substrate conversion through the facilitation of the proton transfer steps
-
-
?
additional information
?
-
the first event in the second halfcycle is the reduction of the HNO intermediate, which is accomplished by two proton-coupled electron transfer reactions. Two isomeric radical intermediates, HNOH radial and H2NO radical, are formed. Both intermediates are readily transformed into hydroxylamine, most likely through intramolecular proton transfer from either Arg114 or His277. An extra proton must enter the active site of the enzyme to initiate heterolytic cleavage of the N-O bond. As a result of N-O bond cleavage, the H2N+ intermediate is formed. It picks up an electron, forming H2N+ radical, which in turn reacts with Tyr218. The intramolecular reaction with Tyr218 in the final step of the nitrite reduction process leads directly to the final product, ammonia. Dissociation of the final product proceeds concomitantly with a change in spin state
-
-
?
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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
nitrite + 4 ferrocytochrome c + 5 H+
hydroxylamine + H2O + 4 ferricytochrome c
-
cf. EC 1.7.2.6
-
-
?
nitrite + acceptor
NH3 + oxidized acceptor + H2O
Q5F2I3
-
-
-
?
NO + 5 ferrocytochrome c + 5 H+
NH3 + H2O + 5 ferricytochrome c
-
important role for the enzyme in nitric oxide management in oxygen-limited environments. Nitric oxide is a key element in host defense against invasive pathogens
-
-
?
sulfite + 6 ferrocytochrome c + 6 H+
H2S + 3 H2O + 6 ferricytochrome c
-
-
-
?
hydroxylamine + ferricytochrome c
nitrite + ferrocytochrome c
-
-
-
-
r
hydroxylamine + ferricytochrome c
nitrite + ferrocytochrome c
-
-
-
r
hydroxylamine + ferricytochrome c
nitrite + ferrocytochrome c
-
-
-
-
r