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Information on EC 1.6.5.5 - NADPH:quinone reductase
for references in articles please use BRENDA:EC1.6.5.5
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EC Tree 1 Oxidoreductases
1.6 Acting on NADH or NADPH
1.6.5 With a quinone or similar compound as acceptor
1.6.5.5 NADPH:quinone reductase
IUBMB Comments
A zinc enzyme, specific for NADPH. Catalyses the one-electron reduction of certain quinones, with the orthoquinones 1,2-naphthoquinone and 9,10-phenanthrenequinone being the best substrates . Dicoumarol [cf. EC 1.6.5.2 NAD(P)H dehydrogenase (quinone)] and nitrofurantoin are competitive inhibitors with respect to the quinone substrate. The semiquinone free-radical product may be non-enzymically reduced to the hydroquinone or oxidized back to quinone in the presence of O2 . In some mammals, the enzyme is abundant in the lens of the eye, where it is identified with the protein ζ-crystallin.
The expected taxonomic range for this enzyme is: Bacteria, Eukaryota, Archaea
- 1.6.5.5
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1.6.99.2
- flavin
- lens
- fmn
- flavoproteins
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two-electron
- dicumarol
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nadph:quinone-acceptor
- hydroquinone
- semiquinone
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bioreductive
- camel
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pentaerythritol
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tetranitrate
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nadph-quinone
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taxon-specific
- 2-methyl-1,4-naphthoquinone
- 5-aziridin-1-yl-2,4-dinitrobenzamide
- morphinone
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1.6.2.4
- 2,4,6-trinitrotoluene
- eo9
- p-hydroxybenzaldehyde
- 9,10-phenanthrenequinone
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explosives
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nitroaromatic
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alpha,beta-unsaturated
- pastorianus
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single-electron
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enones
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2.5.1.18
- environmental protection
- medicine
showSynonyms
zeta-crystallin, old yellow enzyme, vat-1, nadph:quinone oxidoreductase, tcoye, nad(p)h:menadione oxidoreductase, nad(p)h:(quinone-acceptor) oxidoreductase, nad(p)h-quinone reductase, p1-zcr, zta1p, more
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SYNONYM 
ORGANISM
UNIPROT
COMMENTARY 
LITERATURE
Dehydrogenase, reduced nicotinamide adenine dinucleotide (phosphate) (quinone)
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DT-diaphorase
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EC 1.6.99.2
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formerly
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Flavoprotein NAD(P)H:quinone reductase
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Menadione oxidoreductase
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Menadione reductase
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NAD(P)H dehydrogenase
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NAD(P)H dehydrogenase (quinone)
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NAD(P)H menadione reductase
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NAD(P)H quinone reductase
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NAD(P)H-quinone dehydrogenase
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NAD(P)H-quinone oxidoreductase
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NAD(P)H-quinone reductase
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NAD(P)H:(quinone-acceptor) oxidoreductase
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NAD(P)H:menadione oxidoreductase
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NAD(P)H:paraquat diaphorase
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NADH-menadione reductase
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NADH-menaquinone reductase
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NADH:quinone reductase
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NADPH DT-diaphorase
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NADPH:quinone oxidoreductase
NADPH:quinone reductase
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Naphthoquinone reductase
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ORF 17150
p-Benzoquinone reductase
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P1-zeta-crystallin
P36
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Phylloquinone reductase
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Qor
Quinone reductase
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Reduced NAD(P)H dehydrogenase
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Viologen accepting pyridine nucleotide oxidoreductase
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Vitamin K reductase
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zeta-Crystallin
zeta-crystallin homolog protein
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zeta-crystallin/NADPH:quinone oxidoreductase
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zeta-Crystallin/quinone reductase
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Zta1p
NADPH:quinone oxidoreductase
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zeta-Crystallin
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REACTION
REACTION DIAGRAM
COMMENTARY
ORGANISM
UNIPROT
LITERATURE
NADPH + H+ + 2 quinone = NADP+ + 2 semiquinone
reaction with 9,10-phenanthrenequinone and NADPH proceeds through a ping-pong mechanism
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NADPH + H+ + 2 quinone = NADP+ + 2 semiquinone
reaction with 2,6-dichlorophenolindophenol and NADPH proceeds through a ping-pong mechanism
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NADPH + H+ + 2 quinone = NADP+ + 2 semiquinone
enzyme acts through a one-electron transfer process
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NADPH + H+ + 2 quinone = NADP+ + 2 semiquinone
ping pong reaction mechanism
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NADPH + H+ + 2 quinone = NADP+ + 2 semiquinone
catalytic mechanism analysis, two (four)-electron reduction of nitrobenzenes and single-step (H-) hydride transfer mechanism. NfsA follows a ping-pong mechanism, overview
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NADPH + H+ + 2 quinone = NADP+ + 2 semiquinone
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REACTION TYPE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
oxidation
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reduction
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SYSTEMATIC NAME
IUBMB Comments
NADPH:quinone oxidoreductase
A zinc enzyme, specific for NADPH. Catalyses the one-electron reduction of certain quinones, with the orthoquinones 1,2-naphthoquinone and 9,10-phenanthrenequinone being the best substrates [1]. Dicoumarol [cf. EC 1.6.5.2 NAD(P)H dehydrogenase (quinone)] and nitrofurantoin are competitive inhibitors with respect to the quinone substrate. The semiquinone free-radical product may be non-enzymically reduced to the hydroquinone or oxidized back to quinone in the presence of O2 [1]. In some mammals, the enzyme is abundant in the lens of the eye, where it is identified with the protein zeta-crystallin.
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CAS REGISTRY NUMBER
COMMENTARY
9032-20-6
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SUBSTRATE
PRODUCT
REACTION DIAGRAM
ORGANISM
UNIPROT
LITERATURE
COMMENTARY
Reversibility
r=reversible
ir=irreversible
?=not specified
r=reversible
ir=irreversible
?=not specified
1,2-naphthoquinone + NADPH + H+
1,2-naphthoquinol + NADP+
Substrates: -
Products: -
Products: -
?
1,2-naphthoquinone + NADPH + H+
1,2-naphthosemiquinone + NADP+
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Substrates: production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
1,2-naphthoquinone + NADPH + H+
? + NADP+
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Substrates: the activity with 9,10-phenanthrenequinone and with 1,2-naphthoquinone is equal
Products: -
Products: -
?
1,4-benzoquinone + NADPH + H+
1,4-benzosemiquinone + NADP+
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Substrates: production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
1,4-dihydroxy-9,10-anthraquinone + NADPH + H+
anthracene-1,4,9,10-tetrol + NADP+
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Substrates: -
Products: -
Products: -
?
1,8-dihydroxy-9,10-anthraquinone + NADPH + H+
anthracene-1,8,9,10-tetrol + NADP+
-
Substrates: -
Products: -
Products: -
?
2 1,2-naphthoquinone + NADPH + H+
? + NADP+
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Substrates: the activity with 9,10-phenanthrenequinone and with 1,2-naphthoquinone is equal
Products: -
Products: -
?
2 1,4-benzoquinone + NADPH + H+
2 1,4-benzosemiquinone + NADP+
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Substrates: production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
2 1,4-benzoquinone + NADPH + H+
? + NADP+
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Substrates: weak activity
Products: -
Products: -
?
2 1,4-naphthosemiquinone + NADPH + H+
2 1,4-naphthosemiquinone + NADP+
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Substrates: production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
2 5-hydroxy-1,4-naphthoquinone + NADPH + H+
2 5-hydroxy-1,4-naphthosemiquinone + NADP+
-
Substrates: i.e. juglone. Production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
2 5-hydroxy-2-methyl-1,4-naphthoquinone + NADPH + H+
5-hydroxy-2-methyl-1,4-naphthoquinone + NADP+
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Substrates: i.e. plumbagin. Production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
2 9,10-phenanthrenequinone + NADPH + H+
? + NADP+
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Substrates: 70% of the activity with 9,10-phenanthrenequinone
Products: -
Products: -
?
2 decyl-plastoquinone + NADPH + H+
2 decyl-plastosemiquinone + NADP+
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Substrates: production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
2,3,4,6-tetramethyl-1,4-benzoquinone + NADPH + H+
2,3,4,6-tetramethyl-1,4-benzoquinol + NADP+
Substrates: -
Products: -
Products: -
?
2,3-dichloro-1,4-naphthoquinone + NADPH + H+
2,3-dichloro-1,4-naphthoquinol + NADP+
-
Substrates: -
Products: -
Products: -
?
2,3-dimethoxy-5-methyl-1,4-benzoquinone + NADPH + H+
2,3-dimethoxy-5-methyl-1,4-benzoquinol + NADP+
Substrates: -
Products: -
Products: -
?
2,6-dichlorophenolindophenol + NADH + H+
reduced 2,6-dichlorophenolindophenol + NAD+
Substrates: the enzyme is 25times more specific for NADPH as a substrate than for NADH
Products: -
Products: -
?
2,6-dichlorophenolindophenol + NADPH + H+
reduced 2,6-dichlorophenolindophenol + NADP+
Substrates: the enzyme is 25times more specific for NADPH as a substrate than for NADH
Products: -
Products: -
?
2,6-dimethoxy-1,4-benzoquinone + NADPH + H+
2,6-dimethoxy-1,4-benzoquinol + NADP+
Substrates: -
Products: -
Products: -
?
2,6-dimethyl-1,4-benzoquinone + NADPH + H+
2,6-dimethyl-1,4-benzoquinol + NADP+
-
Substrates: -
Products: -
Products: -
?
2-hydroxy-1,4-naphthoquinone + NADPH + H+
naphthalene-1,2,4-triol + NADP+
-
Substrates: -
Products: -
Products: -
?
2-hydroxy-3-methyl-1,4-naphthoquinone + NADPH + H+
3-methylnaphthalene-1,2,4-triol + NADP+
-
Substrates: -
Products: -
Products: -
?
2-methyl-1,4-benzoquinone + NADPH + H+
2-methyl-1,4-benzoquinol + NADP+
-
Substrates: -
Products: -
Products: -
?
4-hydroxy-2-hexenal + NADPH
4-hydroxy-hexanal + NADP+
Substrates: -
Products: -
Products: -
?
4-hydroxy-2-nonenal + NADPH
4-hydroxy-nonanal + NADP+
Substrates: -
Products: -
Products: -
?
5,8-dihydroxy-1,4-naphthoquinone + NADPH + H+
5,8-dihydroxy-1,4-naphthoquinol + NADP+
-
Substrates: -
Products: -
Products: -
?
5-hydroxy-1,4-naphthoquinone + NADPH + H+
5-hydroxy-1,4-naphthosemiquinone + NADP+
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Substrates: i.e. juglone. Production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
5-hydroxy-1,4-naphthoquinone + NADPH + H+
?
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Substrates: i.e. juglone
Products: -
Products: -
?
5-hydroxy-2-methyl-1,4-naphthoquinone + NADPH
5-hydroxy-2-methyl-1,4-naphthoquinol + NADP+
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Substrates: i.e. plumbagin, 0.9% of the activity with 1,2-naphthoquinone
Products: -
Products: -
?
5-hydroxy-2-methyl-1,4-naphthoquinone + NADPH + H+
5-hydroxy-2-methyl-1,4-naphthosemiquinone + NADP+
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Substrates: i.e. plumbagin. Production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
9,10-anthraquinone-2-sulfonic acid + NADPH + H+
9,10-anthraquinol-2-sulfonic acid + NADP+
-
Substrates: -
Products: -
Products: -
?
9,10-phenanthrenequinone + NADPH + H+
9,10-phenanthrenesemiquinone + NADP+
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Substrates: production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
9,10-phenanthrenequinone + NADPH + H+
? + NADP+
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Substrates: the activity with 9,10-phenanthrenequinone and with 1,2-naphthoquinone is equal
Products: -
Products: -
?
ferricytochrome + NADPH + H+
ferrocytochrome + NADP+
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Substrates: -
Products: -
Products: -
?
methyl-1,4-benzoquinone + NADPH
methyl-1,4-benzoquinol + NADP+
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Substrates: 20.6% of the activity with 1,2-naphthoquinone
Products: -
Products: -
?
NADPH + H+ + 2 2,5-dimethyl-4-benzoquinone
NADP+ + 2 2,5-dimethyl-4-benzosemiquinone
-
Substrates: -
Products: -
Products: -
?
NADPH + H+ + 2 2-hydroxy-1,4-naphthoquinone
NADP+ + 2 2-hydroxy-1,4-naphthosemiquinone
-
Substrates: -
Products: -
Products: -
?
NADPH + H+ + 2 anthraquinone-2-sulfonate
NADP+ + ?
-
Substrates: -
Products: -
Products: -
?
NADPH + H+ + 2 dibromothymoquinone
NADP+ + 2 dibromothymosemiquinone
-
Substrates: -
Products: -
Products: -
?
NADPH + H+ + 2 duroquinone
NADP+ + 2 durosemiquinone
-
Substrates: -
Products: -
Products: -
?
NADPH + H+ + komaroviquinone
NADP+ + ?
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Substrates: reduction of komaroviquinone to its semiquinone radical. Antichagasic activity of komaroviquinone is due to generation of reactive oxygen species catalyzed by Trypanosoma cruzi old yellow enzyme
Products: -
Products: -
?
NADPH + H+ + oxidized 2,6-dichlorophenolindophenol
NADP+ + reduced 2,6-dichlorophenolindophenol
O2 + NADH + H+
?
Substrates: the enzyme displays negligible NAD(P)H:oxidase activity
Products: -
Products: -
?
O2 + NADPH + H+
?
Substrates: the enzyme displays negligible NAD(P)H:oxidase activity
Products: -
Products: -
?
tetramethyl-1,4-benzoquinone + NADPH + H+
tetramethyl-1,4-benzoquinol + NADP+
-
Substrates: -
Products: -
Products: -
?
1,2-naphthoquinone + NADPH
1,2-naphthoquinol + NADP+
-
Substrates: -
Products: -
Products: -
?
1,2-naphthoquinone + NADPH
1,2-naphthoquinol + NADP+
-
Substrates: -
Products: -
Products: -
?
1,4-benzoquinone + NADPH
1,4-benzosemiquinone + NADP+
-
Substrates: -
Products: -
Products: -
?
1,4-benzoquinone + NADPH
1,4-benzosemiquinone + NADP+
-
Substrates: 15.3% of the activity with 1,2-naphthoquinone
Products: -
Products: -
?
1,4-benzoquinone + NADPH + H+
1,4-benzoquinol + NADP+
-
Substrates: -
Products: -
Products: -
?
1,4-benzoquinone + NADPH + H+
1,4-benzoquinol + NADP+
Substrates: -
Products: -
Products: -
?
1,4-naphthoquinone + NADPH + H+
1,4-naphthoquinol + NADP+
-
Substrates: -
Products: -
Products: -
?
1,4-naphthoquinone + NADPH + H+
1,4-naphthoquinol + NADP+
Substrates: -
Products: -
Products: -
?
1,4-naphthoquinone + NADPH + H+
1,4-naphthosemiquinone + NADP+
-
Substrates: -
Products: -
Products: -
?
1,4-naphthoquinone + NADPH + H+
1,4-naphthosemiquinone + NADP+
-
Substrates: -
Products: -
Products: -
?
1,4-naphthoquinone + NADPH + H+
1,4-naphthosemiquinone + NADP+
-
Substrates: 2.6% of the activity with 1,2-naphthoquinone
Products: -
Products: -
?
1,4-naphthoquinone + NADPH + H+
1,4-naphthosemiquinone + NADP+
-
Substrates: production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
2 1,2-naphthoquinone + NADPH + H+
2 1,2-naphthosemiquinone + NADP+
-
Substrates: production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
2 1,2-naphthoquinone + NADPH + H+
2 1,2-naphthosemiquinone + NADP+
-
Substrates: -
Products: -
Products: -
?
2 9,10-phenanthrenequinone + NADPH + H+
2 9,10-phenanthrenesemiquinone + NADP+
-
Substrates: production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
2 9,10-phenanthrenequinone + NADPH + H+
2 9,10-phenanthrenesemiquinone + NADP+
-
Substrates: -
Products: -
Products: -
?
2 9,10-phenanthrenequinone + NADPH + H+
2 9,10-phenanthrenesemiquinone + NADP+
-
Substrates: very strong reduction activity towards large substrates such as 9,10-phenanthrenequinone. The zeta-crystallin-like quinone oxidoreductase catalyzes one-electron reduction of certain quinones to generate semiquinone
Products: -
Products: -
?
2-methyl-1,4-naphthoquinone + NADPH + H+
2-methyl-1,4-naphthoquinol + NADP+
-
Substrates: -
Products: -
Products: -
?
2-methyl-1,4-naphthoquinone + NADPH + H+
2-methyl-1,4-naphthoquinol + NADP+
Substrates: -
Products: -
Products: -
?
5-hydroxy-1,4-naphthoquinone + NADPH
5-hydroxy-1,4-naphthosemiquinone + NADP+
-
Substrates: -
Products: -
Products: -
?
5-hydroxy-1,4-naphthoquinone + NADPH
5-hydroxy-1,4-naphthosemiquinone + NADP+
-
Substrates: i.e. juglone, 12.5% of the activity with 1,2-naphthoquinone
Products: -
Products: -
?
5-hydroxy-1,4-naphthoquinone + NADPH + H+
5-hydroxy-1,4-naphthoquinol + NADP+
-
Substrates: -
Products: -
Products: -
?
5-hydroxy-1,4-naphthoquinone + NADPH + H+
5-hydroxy-1,4-naphthoquinol + NADP+
Substrates: -
Products: -
Products: -
?
9,10-phenanthrenequinone + NADPH
9,10-phenanthrenesemiquinone + NADP+
-
Substrates: -
Products: -
Products: -
?
9,10-phenanthrenequinone + NADPH
9,10-phenanthrenesemiquinone + NADP+
-
Substrates: best substrate
Products: -
Products: -
?
9,10-phenanthrenequinone + NADPH
9,10-phenanthrenesemiquinone + NADP+
-
Substrates: -
Products: -
Products: -
?
9,10-phenanthrenequinone + NADPH
9,10-phenanthrenesemiquinone + NADP+
-
Substrates: 50% of the activity with 1,2-naphthoquinone
Products: -
Products: -
?
9,10-phenanthrenequinone + NADPH + H+
9,10-phenanthrenequinol + NADP+
-
Substrates: -
Products: -
Products: -
?
9,10-phenanthrenequinone + NADPH + H+
9,10-phenanthrenequinol + NADP+
Substrates: -
Products: -
Products: -
?
9,10-phenanthrenequinone + NADPH + H+
9,10-phenanthrenequinol + NADP+
Substrates: one-electron reduction mechanism. Concomitantly with NADPH consumption, generation of superoxide is observed
Products: -
Products: -
?
dichlorophenolindophenol + NADPH + H+
reduced dichlorophenolindophenol + NADP+
-
Substrates: -
Products: -
Products: -
?
dichlorophenolindophenol + NADPH + H+
reduced dichlorophenolindophenol + NADP+
-
Substrates: production of semiquinone by univalent catalysts is detectable by the reduction of ferricytochrome c by the semiquinone to ferrocytochrome c
Products: -
Products: -
?
dichlorophenolindophenol + NADPH + H+
reduced dichlorophenolindophenol + NADP+
-
Substrates: -
Products: -
Products: -
?
menadione + NADPH + H+
menadiol + NADP+
Substrates: -
Products: -
Products: -
?
menadione + NADPH + H+
menadiol + NADP+
Substrates: -
Products: -
Products: -
?
menadione + NADPH + H+
menadiol + NADP+
-
Substrates: -
Products: under aerobic conditions, menadiol is readily oxidized to menadione by two 1-electron steps producing the semiquinone and the parent quinone with concomitant production of superoxide anion, which leads to generation of hydroxyl radicals
Products: under aerobic conditions, menadiol is readily oxidized to menadione by two 1-electron steps producing the semiquinone and the parent quinone with concomitant production of superoxide anion, which leads to generation of hydroxyl radicals
?
menadione + NADPH + H+
menadiol + NADP+
Substrates: -
Products: -
Products: -
?
NADPH + H+ + 2 quinone
NADP+ + 2 semiquinone
-
Substrates: the catalytic cycle of ArsH consists of the acceptance of two electrons from NADPH to reduce the flavin cofactor (reductive half-reaction) and the transfer of these electrons to an acceptor (oxidative half-reaction)
Products: -
Products: -
?
NADPH + H+ + oxidized 2,6-dichlorophenolindophenol
NADP+ + reduced 2,6-dichlorophenolindophenol
-
Substrates: -
Products: -
Products: -
?
NADPH + H+ + oxidized 2,6-dichlorophenolindophenol
NADP+ + reduced 2,6-dichlorophenolindophenol
-
Substrates: -
Products: -
Products: -
?
NADPH + H+ + oxidized 2,6-dichlorophenolindophenol
NADP+ + reduced 2,6-dichlorophenolindophenol
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Substrates: 3.8% of the activity with 1,2-naphthoquinone
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Substrates: no activity with: phylloquinone (vitamin K1), menaquinone (vitamin K2), menadione (vitamin K3) and ferricyanide. Preference for o-quinones over p-quinones, and the inability to recognize menadione and ferricyanide as substrates, clearly distinguishe P1-ZCr and guinea-pig ZCr from the flavin-containing NAD(P)H-quinone oxidoreductases in plants and animals. P1-ZCr also catalyzed the divalent reduction of diamide to 1,2-bis(N,N-dimethylcarbamoyl)hydrazine, with a kcat comparable with that for quinones. Two other azodicarbonyl compounds also served as substrates of P1-ZCr. Guinea-pig ZCr, however, did not catalyze the azodicarbonyl reduction. Hence, plant ZCr is distinct from mammalian ZCr, and can be referred to as NADPH:azodicarbonyl/quinone reductase. The quinone-reducing reaction is accompanied by radical chain reactions to produce superoxide radicals, while the azodicarbonyl reducing reaction is not
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Substrates: no activity with menadione and 9,10-anthraquinone
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Substrates: inactive with: menadione, ubiquinone, 9,10-anthraquinone, vitamin K1, vitamin K2
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Substrates: although in the lens the enzyme is considered to be a crystallin, or lens structural protein, because of its high abundance its enzymatic activity and expression at catalytic levels in other tissues of various species suggest that it has a fundamental physiological role outside the lens, perhaps in the detoxification of xenobiotics
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Substrates: no activity with: phylloquinone (vitamin K1), menaquinone (vitamin K2), menadione (vitamin K3), ferricytochrome and ferricyanide. Preference for o-quinones over p-quinones, and the inability to recognize menadione and ferricyanide as substrates, clearly distinguishe Arabidopsis thaliana P1-ZCr and guinea-pig ZCr from the flavin-containing NAD(P)H-quinone oxidoreductases in plants and animals
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Substrates: NADPH-dependent reduction of quinones and nitroaromatic compounds by NfsA, overview. The reactivity of nitroaromatic compounds (log kcat/Km) follows a linear dependence on their single-electron reduction potential, indicating a limited role for compound structure or active site flexibility in their reactivity. The reactivity of quinones is lower than that of nitroaromatics having similar single-electron reduction potential values, except for the significantly enhanced reactivity of 2-OH-1,4-naphthoquinones. The reduction of quinones by NfsA is most consistent with a single-step (H-) hydride transfer mechanism, quantitative analysis of two-electron reduction of quinones and nitroaromatics, overview
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Substrates: coenzyme Q and tetracycline may be used as electron acceptors, but with much lower specific activities than menadione. Nitro compounds dinitrotoluene, 7-nitrocoumarin, and metronidazole can be used as electron acceptors
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Substrates: coenzyme Q and tetracycline may be used as electron acceptors, but with much lower specific activities than menadione. Nitro compounds dinitrotoluene, 7-nitrocoumarin, and metronidazole can be used as electron acceptors
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Substrates: coenzyme Q and tetracycline may be used as electron acceptors, but with much lower specific activities than menadione. Nitro compounds dinitrotoluene, 7-nitrocoumarin, and metronidazole can be used as electron acceptors
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Substrates: although in the lens the enzyme is considered to be a crystallin, or lens structural protein, because of its high abundance its enzymatic activity and expression at catalytic levels in other tissues of various species suggest that it has a fundamental physiological role outside the lens, perhaps in the detoxification of xenobiotics
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Substrates: the human and yeast enzymes specifically bind to adenine-uracil rich elements (ARE) in RNA, indicating that both enzymes are ARE-binding proteins and that this property has been conserved in zeta-crystallins throughout evolution. This supports a role for zeta-crystallins as trans-acting factors that could regulate the turnover of certain mRNAs
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Substrates: enzyme reduces ortho-quinones in the presence of NADPH but is not active with 2-alkenals
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Substrates: the enzyme does not exhibit nitronate monooxygenase activity (no activity with propionate 3-nitronate, 3-nitropropionate, nitroethane, 2-nitropropane, ethylnitronate, or propyl-2-nitronate) and does not turn over with methyl red, consistent with a lack of azoreductase activity
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Substrates: the human and yeast enzymes specifically bind to adenine-uracil rich elements (ARE) in RNA, indicating that both enzymes are ARE-binding proteins and that this property has been conserved in zeta-crystallins throughout evolution. This supports a role for zeta-crystallins as trans-acting factors that could regulate the turnover of certain mRNAs
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Substrates: enzyme reduces ortho-quinones in the presence of NADPH but is not active with 2-alkenals
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Substrates: although the enzyme is able to stabilize the anionic semiquinone form of the FMN, reduction of quinones involves the hydroquinone form of the flavin cofactor, and the enzymatic reaction occurs through a ping pong-type mechanism. ArsH is able to catalyze one-electron reactions (oxygen and cytocrome c reduction), involving the FMN semiquinone form, but with lower efficiency
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Substrates: QR1 catalyzes the univalent reduction of quinones to semiquinone radicals
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Substrates: QR1 catalyzes the univalent reduction of quinones to semiquinone radicals
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NATURAL SUBSTRATE
NATURAL PRODUCT
REACTION DIAGRAM
ORGANISM
UNIPROT
LITERATURE
COMMENTARY
REVERSIBILITY
r=reversible
ir=irreversible
?=not specified
r=reversible
ir=irreversible
?=not specified
additional information
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Substrates: although in the lens the enzyme is considered to be a crystallin, or lens structural protein, because of its high abundance its enzymatic activity and expression at catalytic levels in other tissues of various species suggest that it has a fundamental physiological role outside the lens, perhaps in the detoxification of xenobiotics
Products: -
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additional information
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Substrates: although in the lens the enzyme is considered to be a crystallin, or lens structural protein, because of its high abundance its enzymatic activity and expression at catalytic levels in other tissues of various species suggest that it has a fundamental physiological role outside the lens, perhaps in the detoxification of xenobiotics
Products: -
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additional information
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Substrates: the human and yeast enzymes specifically bind to adenine-uracil rich elements (ARE) in RNA, indicating that both enzymes are ARE-binding proteins and that this property has been conserved in zeta-crystallins throughout evolution. This supports a role for zeta-crystallins as trans-acting factors that could regulate the turnover of certain mRNAs
Products: -
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additional information
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Substrates: the human and yeast enzymes specifically bind to adenine-uracil rich elements (ARE) in RNA, indicating that both enzymes are ARE-binding proteins and that this property has been conserved in zeta-crystallins throughout evolution. This supports a role for zeta-crystallins as trans-acting factors that could regulate the turnover of certain mRNAs
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COFACTOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
NADH
the enzyme can be reduced with NADPH or NADH with a marked preference for NADPH
NADPH
interference of NADPH on Zta1p binding to RNA is much lower than that of NADPH on human zeta-crystallin, consistent with a weaker binding of NADPH to the yeast enzyme
NADPH
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NADPH binding causes conformational changes in the structure of the enzyme
NADPH
NADPH, but not NADH, competitively prevents binding of zeta-crystallin to RNA, suggesting that the cofactor-binding site is involved in RNA binding
NADPH
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specificity to NADPH, as judged by kcat/Km, is more than 1000fold higher than that to NADH
NADPH
NADPH is located in the cleft between domains I and II. The adenine ring is sandwiched between the main chains of Ala220 and Glu221 and the side chain of Arg292. Ala220 and Glu221 are disordered in apo-QOR
NADPH
the enzyme can be reduced with NADPH or NADH with a marked preference for NADPH
additional information
no cofactor: NADH. Sequence does not contain a flavin-binding motif
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additional information
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no cofactor: NADH. Sequence does not contain a flavin-binding motif
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INHIBITOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
2,5-Dichloro-3,6-dihydroxy-1,4-benzoquinone
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i.e. chloranilic acid, noncompetitive with respect to both NADPH and 9,10-phenanthrenequinone
4-chloromercuribenzoate
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both NADPH and NADP1 suppress the inhibition, but NADH does not
4-Hydroxycoumarin
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reversible time-independent inhibition. Only dicoumarol, 4-hydroxycoumarin and warfarin inhibit in micromolar ranges. 7-Hydroxy-4-methylcoumarin is ineffective. Competitive inhibition with respect to 2,6-dichlorophenolindophenol, uncompetitive with respect to NADPH. Phenolic hydroxyl group at the C-4 position in the coumarin skeleton is important for the maximal inhibition. Sequence of potency for the inhibitors in descending order: dicoumarol, 4-hydroxycoumarin, warfarin, coumarin
Colchicine
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noncompetitive with respect to 9,10-phenanthrenequinone and 1,2-naphthoquinone, uncompetitive with respect to NADPH. Binding of colchicine occurs at or close to the NADPH binding site
coumarin
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reversible time-independent inhibition. Only dicoumarol, 4-hydroxycoumarin and warfarin inhibit in micromolar ranges. 7-Hydroxy-4-methylcoumarin is ineffective. Competitive inhibition with respect to 2,6-dichlorophenolindophenol, uncompetitive with respect to NADPH. Phenolic hydroxyl group at the C-4 position in the coumarin skeleton is important for the maximal inhibition. Sequence of potency for the inhibitors in descending order: dicoumarol, 4-hydroxycoumarin, warfarin, coumarin
emodin
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i.e. an anthraquinone, inhibits the enzymatic activity of NADPH-quinone reductase by binding to the active site. Emodin acts as a competitive inhibitor with respect to 2, 6-dichlorophenolindophenol, and emodin shows cytotoxicity against rat hepatocytes
N-ethylmaleimide
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both NADPH and NADP1 suppress the inhibition, but NADH does not
NADPH
substrate inhibition is observed at NADPH concentrations of more than 0.05 mM
pyridoxal-5'-phosphate
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inactivation follows pseudo-first-order kinetics. NADPH protects against inactivation, 9,10-phenanthrenequinone does not protect. Inhibition is uncompetitive with NADPH and non-competitive with respect to 9,10-phenanthrenequinone
5,5'-dithiobis(2-nitrobenzoate)
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inactivation is caused by a modification of one Cys per subunit, reactivation by dithiothreitol or KCN. NADPH partially protects from inactivation, 9,10-phenanthrenequinone enhances the modification
Cibacron blue 3GA
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inhibits the reaction with NADPH and 9,10-phenanthrenequinone. Linear mixed type inhibition with respect to NADPH and noncompetitive with respect to 9,10-phenanthrenequinone
dicoumarol
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competitive with respect to 2,6-dichlorophenol-indophenol, uncompetitive with respect to NADPH
dicoumarol
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reversible time-independent inhibition. Only dicoumarol, 4-hydroxycoumarin and warfarin inhibit in micromolar ranges. 7-Hydroxy-4-methyl