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Information on EC 1.8.1.2 - assimilatory sulfite reductase (NADPH)
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EC Tree
1.8.1.2 assimilatory sulfite reductase (NADPH)IUBMB Comments
Contains siroheme, [4Fe-4S] cluster, FAD and FMN. The enzyme, which catalyses the six-electron reduction of sulfite to sulfide, is involved in sulfate assimilation in bacteria and yeast. Different from EC 1.8.99.5, dissimilatory sulfite reductase, which is involved in prokaryotic sulfur-based energy metabolism. cf. EC 1.8.7.1, assimilatory sulfite reductase (ferredoxin).
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Word Map
- 1.8.1.2
- sulfur
- siroheme
-
dissimilatory
- hemoprotein
- desulfovibrio
-
sulfate-reducing
- thiosulfate
-
six-electron
-
desulfoviridin
- o-acetylserine
-
sulfhydrylase
- dsrab
-
sulfurylase
- 5'-phosphosulfate
- hildenborough
-
ferredoxin-dependent
- o-acetyl-l-serine
-
exchange-coupled
- desulfotomaculum
- brewing
- nutrition
- medicine
- synthesis
The expected taxonomic range for this enzyme is: Bacteria, Eukaryota, Archaea
Synonyms
sulfite reductase, met10, sir-fp, sir-hp, nadph-sulfite reductase, sirhp, desulforubidin, cysij, nadph-dependent sulfite reductase, coenzyme f420-dependent sulfite reductase, 
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SYNONYM 
ORGANISM
UNIPROT
COMMENTARY 
LITERATURE
CNG03990
CysIJ
desulforubidin
-
-
-
-
EC 1.8.99.1
-
-
formerly, part transferred
-
H2S-NADP oxidoreductase
-
-
-
-
MET10
NADPH-dependent sulfite reductase
NADPH-sulfite reductase
reductase, sulfite (reduced nicotinamide adenine dinucleotide phosphate)
-
-
-
-
SIR
SIR-FP
-
-
-
-
SIR-HP
SiR/SiRHP
SIRHP
-
-
-
-
sulfite reductase
NADPH-dependent sulfite reductase
-
-
-
-
NADPH-sulfite reductase
-
-
-
-
SIR-HP
-
-
-
-
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REACTION
REACTION DIAGRAM
COMMENTARY
ORGANISM
UNIPROT
LITERATURE
hydrogen sulfide + 3 NADP+ + 3 H2O = sulfite + 3 NADPH + 3 H+
-
-
-
-
hydrogen sulfide + 3 NADP+ + 3 H2O = sulfite + 3 NADPH + 3 H+
ping-pong mechanism
-
hydrogen sulfide + 3 NADP+ + 3 H2O = sulfite + 3 NADPH + 3 H+
mechanism of electron transfer
-
hydrogen sulfide + 3 NADP+ + 3 H2O = sulfite + 3 NADPH + 3 H+
electron flow sequence: NADPH-FAD-FMN
-
hydrogen sulfide + 3 NADP+ + 3 H2O = sulfite + 3 NADPH + 3 H+
electron flow sequence: NADPH-FAD-FMN
-
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REACTION TYPE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
oxidation
redox reaction
-
-
-
-
reduction
additional information
oxidation
-
-
-
-
reduction
-
-
-
-
additional information
-
sodium salts of thiosulfate and sulfate do not serve as the electron acceptor for reduced F420 oxidation by Fsr. Also, Fsr can not use NADH and NADPH for the reduction of sulfite.
additional information
-
the N-terminal half of Fsr represents a H2F420 dehydrogenase and the C-terminal half a dissimilatory-type siroheme sulfite reductase, and Fsr catalyzes the corresponding partial reactions
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PATHWAY SOURCE
PATHWAYS
BRENDA
-
,
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SYSTEMATIC NAME
IUBMB Comments
hydrogen-sulfide:NADP+ oxidoreductase
Contains siroheme, [4Fe-4S] cluster, FAD and FMN. The enzyme, which catalyses the six-electron reduction of sulfite to sulfide, is involved in sulfate assimilation in bacteria and yeast. Different from EC 1.8.99.5, dissimilatory sulfite reductase, which is involved in prokaryotic sulfur-based energy metabolism. cf. EC 1.8.7.1, assimilatory sulfite reductase (ferredoxin).
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CAS REGISTRY NUMBER
COMMENTARY
9029-35-0
-
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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
1,1'-dimethyl-4,4'-bipyridinium dichloride + NADPH
NADPH + oxidized 1,1'-dimethyl-4,4'-bipyridinium dichloride
-
i.e. paraquat, a herbicide
-
-
?
hydrogen sulfide + 3 NADP+ + 3 H2O
sulfite + 3 NADPH + 3 H+
-
-
-
-
?
NADP+ + reduced methyl viologen
NADPH + oxidized methyl viologen
-
-
-
-
?
hydroxylamine + NADPH
ammonia + NADP+
-
NADPH can be replaced by reduced methyl viologen
-
?
nitrite + NADPH
ammonia + NADP+
-
NADPH can be replaced by reduced methyl viologen, the latter reaction is catalyzed by hemoprotein subunit alone
-
-
?
nitrite + NADPH
ammonia + NADP+
-
-
-
-
?
sulfite + 3 NADPH + 3 H+
hydrogen sulfide + 3 NADP+ + 3 H2O
-
-
-
?
sulfite + 3 NADPH + 3 H+
hydrogen sulfide + 3 NADP+ + 3 H2O
-
essential enzyme in the global sulfur cycle
-
-
?
sulfite + 3 NADPH + 3 H+
hydrogen sulfide + 3 NADP+ + 3 H2O
the electron transfer occurs via multiple pathways, bypassing the need for electrons to move intra-molecularly from the NADH to the FAD to the FMN and then in cis to SiRHP. In this way, SiR effectively raises the local concentration of electrons relative to SiRHP active sites to facilitate the full six electron reduction of SO32- to S2-
-
-
?
sulfite + 3 NADPH + 3 H+
hydrogen sulfide + 3 NADP+ + 3 H2O
-
-
-
?
sulfite + NADPH
sulfide + NADP+ + H2O
-
reduction of sulfite by reduced methyl viologen is catalyzed by hemoprotein subunit alone
-
-
?
sulfite + NADPH
sulfide + NADP+ + H2O
-
NADPH can be replaced by reduced methyl viologen
-
-
?
sulfite + NADPH
sulfide + NADP+ + H2O
-
NADPH can be replaced by reduced methyl viologen
-
?
sulfite + NADPH
sulfide + NADP+ + H2O
-
reduction of sulfite by reduced methyl viologen is catalyzed by hemoprotein subunit alone
-
-
?
sulfite + NADPH
sulfide + NADP+ + H2O
-
NADPH can be replaced by reduced methyl viologen
-
-
?
sulfite + NADPH
sulfide + NADP+ + H2O
-
-
-
-
?
sulfite + NADPH
sulfide + NADP+ + H2O
-
reduction of sulfite by reduced methyl viologen is catalyzed by hemoprotein subunit alone
-
-
?
sulfite + NADPH + H+
sulfide + NADP+ + H2O
-
no physiological nitrite reductase
-
-
?
additional information
?
-
the enzyme catalyzes the reduction of sulfite to sulfide
-
-
-
additional information
?
-
the enzyme catalyzes the reduction of sulfite to sulfide
-
-
-
additional information
?
-
the enzyme catalyzes the reduction of sulfite to sulfide
-
-
-
additional information
?
-
-
transfer of hydrogen from NADPH to 3-acetylpyridineadenine dinucleotide phosphate
-
-
?
additional information
?
-
-
transfer of hydrogen from NADPH to 3-acetylpyridineadenine dinucleotide phosphate
-
-
?
additional information
?
-
-
transfer of hydrogen from NADPH to 3-acetylpyridineadenine dinucleotide phosphate
-
-
?
additional information
?
-
-
reduction of sulfite, nitrite, and hydroxylamine by NADPH requires catalytic activities of both subunits, reduction of sulfite, nitrite, and hydroxylamine by methyl viologen requires hemoprotein subunit
-
-
?
additional information
?
-
-
reduction of sulfite, nitrite, and hydroxylamine by NADPH requires catalytic activities of both subunits, reduction of sulfite, nitrite, and hydroxylamine by methyl viologen requires hemoprotein subunit
-
-
?
additional information
?
-
-
reduction of sulfite, nitrite, and hydroxylamine by NADPH requires catalytic activities of both subunits, reduction of sulfite, nitrite, and hydroxylamine by methyl viologen requires hemoprotein subunit
-
-
?
additional information
?
-
-
reactions catalyzed by flavoprotein subunit alone: transfer of electrons from NADPH to cytochrome c, ferricyanide, dichlorphenolindophenol, menadione, FMN, FAD, O2
-
-
?
additional information
?
-
-
reactions catalyzed by flavoprotein subunit alone: transfer of electrons from NADPH to cytochrome c, ferricyanide, dichlorphenolindophenol, menadione, FMN, FAD, O2
-
-
?
additional information
?
-
-
reactions catalyzed by flavoprotein subunit alone: transfer of electrons from NADPH to cytochrome c, ferricyanide, dichlorphenolindophenol, menadione, FMN, FAD, O2
-
-
?
additional information
?
-
-
reactions catalyzed by flavoprotein subunit alone: transfer of electrons from NADPH to cytochrome c, ferricyanide, dichlorphenolindophenol, menadione, FMN, FAD, O2
-
-
?
additional information
?
-
-
can generate tyrosil radicals e.g. for transfer of electrons to the iron center of metR2, small subunit of ribonucletide reductase
-
-
?
additional information
?
-
-
transfer of hydrogen from NADPH to 3-acetylpyridineadenine dinucleotide phosphate
-
-
?
additional information
?
-
-
reduction of sulfite, nitrite, and hydroxylamine by NADPH requires catalytic activities of both subunits, reduction of sulfite, nitrite, and hydroxylamine by methyl viologen requires hemoprotein subunit
-
-
?
additional information
?
-
-
reactions catalyzed by flavoprotein subunit alone: transfer of electrons from NADPH to cytochrome c, ferricyanide, dichlorphenolindophenol, menadione, FMN, FAD, O2
-
-
?
additional information
?
-
-
reactions catalyzed by flavoprotein subunit alone: transfer of electrons from NADPH to cytochrome c, ferricyanide, dichlorphenolindophenol, menadione, FMN, FAD, O2
-
-
?
additional information
?
-
-
reactions catalyzed by flavoprotein subunit alone: transfer of electrons from NADPH to cytochrome c, ferricyanide, dichlorphenolindophenol, menadione, FMN, FAD, O2
-
-
?
additional information
?
-
-
reactions catalyzed by flavoprotein subunit alone: transfer of electrons from NADPH to cytochrome c, ferricyanide, dichlorphenolindophenol, menadione, FMN, FAD, O2
-
-
?
additional information
?
-
-
by production of the population synchronizer H2S involved in ultradian metabolic oscillation
-
-
?
additional information
?
-
-
transfer of hydrogen from NADPH to 3-acetylpyridineadenine dinucleotide phosphate
-
-
?
additional information
?
-
-
transfer of hydrogen from NADPH to 3-acetylpyridineadenine dinucleotide phosphate
-
-
?
additional information
?
-
-
reduction of sulfite, nitrite, and hydroxylamine by NADPH requires catalytic activities of both subunits, reduction of sulfite, nitrite, and hydroxylamine by methyl viologen requires hemoprotein subunit
-
-
?
additional information
?
-
-
reduction of sulfite, nitrite, and hydroxylamine by NADPH requires catalytic activities of both subunits, reduction of sulfite, nitrite, and hydroxylamine by methyl viologen requires hemoprotein subunit
-
-
?
additional information
?
-
-
reactions of FMN depleted enzyme
-
-
?
additional information
?
-
-
reactions catalyzed by flavoprotein subunit alone: transfer of electrons from NADPH to cytochrome c, ferricyanide, dichlorphenolindophenol, menadione, FMN, FAD, O2
-
-
?
additional information
?
-
-
reactions catalyzed by flavoprotein subunit alone: transfer of electrons from NADPH to cytochrome c, ferricyanide, dichlorphenolindophenol, menadione, FMN, FAD, O2
-
-
?
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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
hydrogen sulfide + 3 NADP+ + 3 H2O
sulfite + 3 NADPH + 3 H+
-
-
-
-
?
sulfite + 3 NADPH + 3 H+
hydrogen sulfide + 3 NADP+ + 3 H2O
-
-
-
?
sulfite + 3 NADPH + 3 H+
hydrogen sulfide + 3 NADP+ + 3 H2O
-
essential enzyme in the global sulfur cycle
-
-
?
sulfite + 3 NADPH + 3 H+
hydrogen sulfide + 3 NADP+ + 3 H2O
-
-
-
?
sulfite + NADPH + H+
sulfide + NADP+ + H2O
-
no physiological nitrite reductase
-
-
?
additional information
?
-
-
can generate tyrosil radicals e.g. for transfer of electrons to the iron center of metR2, small subunit of ribonucletide reductase
-
-
?
additional information
?
-
-
by production of the population synchronizer H2S involved in ultradian metabolic oscillation
-
-
?
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COFACTOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
FAD
flavoprotein. The electron transfer occurs via multiple pathways, bypassing the need for electrons to move intra-molecularly from the NADH to the FAD to the FMN and then in cis to SiRHP. In this way, SiR effectively raises the local concentration of electrons relative to SiRHP active sites to facilitate the full six electron reduction of SO32- to S2-
flavin
-
treatment with ammonium sulfate causes dissociation of FMN but retetion of FAD and heme
flavin
-
4 FAD and 4 FMN per mol of enzyme
flavin
-
treatment with p-chloromercuriphenylsulfonate causes dissociation of FMN but retetion of FAD and heme
heme
-
tetrahydroporphyrin of isobacteriochlorin type with eight carboxylic side chains
heme
-
2 fully metallated sirohemes per mol of enzyme, S=9/2 EPR iron-sulfur cluster
heme
-
hemoprotein subunit contains one siroheme and one Fe4S4 center per polypeptide
siroheme
siroheme-containing subunit of the multimeric hemoflavoprotein NADPH-dependent sulfite reductase. Siroheme is an iron-containing isobacteriochlorin, that does not work alone but is covalently coupled to a Fe4S4 cluster through one of the cluster's ligands
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METALS and IONS
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
Iron-sulfur cluster
Iron-sulfur cluster
-
4Fe-4S, 4 mol per tetramer of hemoprotein subunit, bound to hemoprotein subunit
Iron-sulfur cluster
-
hemoprotein subunit contains one siroheme and one Fe4S4 center per polypeptide, heme is in high spin Fe3+ state
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INHIBITOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
iodonium diphenyl chloride
-
acts on NADPH- and FAD-binding domain of flavoprotein component
p-chloromercuribenzoate
-
NADPH-dependent activities
additional information
-
inhibitory potency of metal ions, overview, no inhibition by Na+, K+, and Mg2+
-
CN-
-
severe inhibition of NADPH-sulfite,-nitrite,-hydroxylamine reductase, no inhibition of methyl viologen-sulfite reductase, small extent of inhibition of NADPH dependent reduction of cytochrome c, ferricyanide, quinones etc.
CN-
-
only when added with NADPH prior to substrate, sulfite prevents NADPH-reduced form from irreversible conversion by CN-; severe inhibition of NADPH-sulfite,-nitrite,-hydroxylamine reductase, no inhibition of methyl viologen-sulfite reductase, small extent of inhibition of NADPH dependent reduction of cytochrome c, ferricyanide, quinones etc.
Sulfide
-
reduction of sulfite, nitrite, hydroxylamine by reduced methyl viologen
Sulfide
-
reduction of sulfite, nitrite, hydroxylamine by reduced methyl viologen
Sulfide
-
reduction of sulfite, nitrite, hydroxylamine by reduced methyl viologen
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ACTIVATING COMPOUND
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
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DISEASE
TITLE OF PUBLICATION
LINK TO PUBMED
Invasive Pulmonary Aspergillosis
Exploration of Sulfur Assimilation of Aspergillus fumigatus Reveals Biosynthesis of Sulfur-Containing Amino Acids as a Virulence Determinant.
Starvation
Sulfite Reductase Co-suppression in Tobacco Reveals Detoxification Mechanisms and Downstream Responses Comparable to Sulfate Starvation.
Starvation
Transcriptional and Proteomic Profiling of Aspergillus flavipes in Response to Sulfur Starvation.
Tuberculosis
Siroheme- and [Fe4-S4]-dependent NirA from Mycobacterium tuberculosis is a sulfite reductase with a covalent Cys-Tyr bond in the active site.
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KM VALUE [mM]
SUBSTRATE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
0.021
reduced F420
-
at a fixed sulfite concentration of 0.29 mM and within a reduced F420 concentration range of 0.004-0.06 mM
0.08
FAD