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Information on EC 1.7.2.2 - nitrite reductase (cytochrome; ammonia-forming) and Organism(s) Shewanella oneidensis and UniProt Accession Q8EAC7
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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
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dissimilatory
- succinogenes
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wolinella
- nitrosomonas
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ammonification
- thioalkalivibrio
- nitratireducens
- desulfuricans
- chromatium
- flavorubredoxin
- deleyianum
- menaquinol
- hydrogenobacter
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pentahaem
- hildenborough
- sulfurospirillum
- ferrocytochrome
- flavohemoglobins
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cxxch
- analysis
The taxonomic range for the selected organisms is: Shewanella oneidensis
The enzyme appears in selected viruses and cellular organisms
The enzyme appears in selected 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, sco2488, nrfa2nrfh complex, 
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topSYNONYM 
ORGANISM
UNIPROT
COMMENTARY 
LITERATURE
cytochrome c nitrite reductase
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multiheme nitrite reductase
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REACTION TYPE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
redox reaction
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oxidation
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reduction
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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.
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
nitrite + reduced + acceptor
NH3 + oxidized acceptor + H2O
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?
nitrite + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
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?
additional information
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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
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?
additional information
?
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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
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additional information
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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
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additional information
?
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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
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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 + 6 ferrocytochrome c + 7 H+
NH3 + 2 H2O + 6 ferricytochrome c
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COFACTOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
cytochrome c
an enzyme-bound c-type cytochrome with a non-canonical CX2CK motif. CcmI, i.e. cytochrome c maturation system I, an apocytochrome c chaperone, is important and essential for maturation of c-type cytochromes with the non-canonical heme binding motif (HBM) CX2CK, presumably by ensuring that heme attachment at canonical HBMs occurs before apoprotein degradation. Both CcmISo-1 and CcmISo-2 are required for maturation of NrfA. The periplasmic portion of CcmI, CcmI-2, interacts with C-terminus of enzyme NrfA. Heme attachment to the apoprotein is achieved stereochemically by linking of the 2-vinyl and 4-vinyl of heme b via thioether bonds to the N-terminal and C-terminal cysteines, respectively, within heme binding motif. NrfASo is unstable unless heme attachment is timely accomplished, the failure of heme ligation in NrfASo results in rapid degradation, NrfA is rapidly degraded unless properly maturated
INHIBITOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
KM VALUE [mM]
SUBSTRATE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
TURNOVER NUMBER [1/s]
SUBSTRATE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
Ki VALUE [mM]
INHIBITOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
ORGANISM
COMMENTARY
LITERATURE
UNIPROT
SEQUENCE DB
SOURCE
GENERAL INFORMATION
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
metabolism
physiological function
gene SO0265 encodes CcmI, an apocytochrome c chaperone, that is important and essential for maturation of c-type cytochromes with the canonical heme binding motif(s) (HBM and CX2CH) and nitrite reductase NrfA carrying a non-canonical CX2CK motif, respectively. The N-terminal transmembrane segment of CcmI, CcmI-1, is sufficient for maturation of the former but the entire protein is required for maturation of the latter. SirE is not required for maturation of NrfA
metabolism
nitrite-loaded ccNiR is reduced in a concerted two-electron step to generate an [FeNO]7 moiety at the active site, with an associated midpoint potential of +246 mV vs standard hydrogen electrode at pH 7. Cyanide-bound active site reduction is a one-electron process with a midpoint potential of +20 mV, and without a strong-field ligand the active site midpoint potential shifts 70 mV lower still. The [FeNO]7 moiety possesses an spectral signature, different from those normally observed for [FeNO]7 hemes, that may indicate magnetic interaction of the active site with nearby hemes. Catalytic nitrite reduction to ammonia by ccNiR requires an applied potential of at least -120 mV, well below the midpoint potential for [FeNO]7 formation
metabolism
reduction of nitrite-loaded ccNiR by N,N,N',N'-tetramethyl-pphenylenediamine generates a transient intermediate, identified as FeH1II(NO2-), where FeH1 represents the ccNiR active site. FeH1II(NO2-) accumulates rapidly and is then more slowly converted to the two-electron-reduced moiety [FeH1NO]7. ccNiR is not reduced beyond the [FeH1NO]7 state. The midpoint potentials for sequential reduction of FeH1III(NO2-) to FeH1II(NO2-) and then to [FeH1NO]7 are 130 and 370 mV versus the standard hydrogen electrode, respectively. With weak reductants, free NO radical is released from nitrite-loaded ccNiR
PDB
SCOP
CATH
UNIPROT
ORGANISM
CRYSTALLIZATION (Commentary)
ORGANISM
UNIPROT
LITERATURE
UV/Vis spectropotentiometric results yield highly reproducible values for the heme midpoint potentials, which can be assigned to specific hemes in each protomer. Addition of the strong-field ligand cyanide leads to a 70 mV positive shift of the active site's midpoint potential, the cyanide binds to the initially 5-coordinate high-spin heme and triggers a high-spin to low-spin transition. With cyanide present three of the remaining hemes give rise to distinctive and readily assignable EPR spectral changes upon reduction
PROTEIN VARIANTS
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
H268M
one of the EPR-silent heme's histidine axial ligands is replaced with a methionine
K119H
site-directed mutagensis, mutation of the essential lysine residue of the non-canonical HBM (CX2CK), inactive mutant. The mutant NrfA protein displays a similar pattern of rapid degradation like the wild-type without maturation
K119L
site-directed mutagensis, mutation of the essential lysine residue of the non-canonical HBM (CX2CK), inactive mutant. The mutant NrfA protein displays a similar pattern of rapid degradation like the wild-type without maturation
additional information
costruction of a DELTAnrfA mutant enzyme knockout strain, expression of the wild-type enzyme from vector pHG101 can restore the enzyme activity, but not expression of enzyme mutants K119L and K119H
GENERAL STABILITY
ORGANISM
UNIPROT
LITERATURE
NrfASo is unstable unless heme attachment is timely accomplished
CLONED (Commentary)
ORGANISM
UNIPROT
LITERATURE
recombinant expression of wild-type and mutant enzymes in Escherichia coli
APPLICATION
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
analysis
trapping of a putative intermediate by controlling the electrochemical potential at which reduction takes place. An [FeNO}]7 active site is a catalytic intermediate in the ccNiR-mediated reduction of nitrite to ammonia. At low potentials the species is rapidly reduced and does not accumulate, while at higher potentials it is trapped, thus preventing catalytic ammonia formation
REF.
AUTHORS
TITLE
JOURNAL
VOL.
PAGES
YEAR
ORGANISM (UNIPROT)
PUBMED ID
SOURCE
Judd, E.T.; Youngblut, M.; Pacheco, A.A.; Elliott, S.J.
Direct electrochemistry of Shewanella oneidensis cytochrome c nitrite reductase: evidence of interactions across the dimeric interface
Biochemistry
51
10175-10185
2012
Shewanella oneidensis (Q8EAC7), Shewanella oneidensis
Youngblut, M.; Pauly, D.J.; Stein, N.; Walters, D.; Conrad, J.A.; Moran, G.R.; Bennett, B.; Pacheco, A.A.
Shewanella oneidensis cytochrome c nitrite reductase (ccNiR) does not disproportionate hydroxylamine to ammonia and nitrite, despite a strongly favorable driving force
Biochemistry
53
2136-2144
2014
Shewanella oneidensis (Q8EAC7), Shewanella oneidensis
Stein, N.; Love, D.; Judd, E.T.; Elliott, S.J.; Bennett, B.; Pacheco, A.A.
Correlations between the electronic properties of Shewanella oneidensis cytochrome c nitrite reductase (ccNiR) and its structure effects of heme oxidation state and active site ligation
Biochemistry
54
3749-3758
2015
Shewanella oneidensis (Q8EAC7), Shewanella oneidensis
Fu, H.; Jin, M.; Wan, F.; Gao, H.
Shewanella oneidensis cytochrome c maturation component CcmI is essential for heme attachment at the non-canonical motif of nitrite reductase NrfA
Mol. Microbiol.
95
410-425
2015
Shewanella oneidensis (Q8EHC7)
Shahid, S.; Ali, M.; Legaspi-Humiston, D.; Wilcoxen, J.; Pacheco, A.A.
A kinetic investigation of the early steps in cytochrome c nitrite reductase (ccNiR)-catalyzed reduction of nitrite
Biochemistry
60
2098-2115
2021
Shewanella oneidensis (Q8EAC7), Shewanella oneidensis
Ali, M.; Stein, N.; Mao, Y.; Shahid, S.; Schmidt, M.; Bennett, B.; Pacheco, A.A.
Trapping of a putative intermediate in the cytochrome c nitrite Reductase (ccNiR)-catalyzed reduction of nitrite Implications for the ccNiR reaction mechanism
J. Am. Chem. Soc.
141
13358-13371
2019
Shewanella oneidensis (Q8EAC7), Shewanella oneidensis
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