Information on EC 1.17.98.1 - bile-acid 7alpha-dehydroxylase

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The enzyme appears in viruses and cellular organisms

EC NUMBER
COMMENTARY hide
1.17.98.1
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RECOMMENDED NAME
GeneOntology No.
bile-acid 7alpha-dehydroxylase
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REACTION
REACTION DIAGRAM
COMMENTARY hide
ORGANISM
UNIPROT
LITERATURE
deoxycholate + FAD + H2O = cholate + FADH2
show the reaction diagram
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lithocholate + FAD + H2O = chenodeoxycholate + FADH2
show the reaction diagram
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SYSTEMATIC NAME
IUBMB Comments
deoxycholate:FAD oxidoreductase (7alpha-dehydroxylating)
Under physiological conditions, the reactions form deoxycholate. This enzyme is highly specific for bile-acid substrates and requires a free C-24 carboxy group and an unhindered 7alpha-hydroxy group on the B-ring of the steroid nucleus for activity, as found in cholate and chenodeoxycholate. The reaction is stimulated by the presence of NAD+ but is inhibited by excess NADH. This unusual regulation by the NAD+/NADH ratio is most likely the result of the intermediates being linked at C-24 by an anhydride bond to the 5'-diphosphate of 3'-phospho-ADP [2,5,6]. Allodeoxycholate is also formed as a side-product of the 7alpha-dehydroxylation of cholate [6]. The enzyme is present in intestinal anaerobic bacteria [6], even though its products are important in mammalian physiology.
CAS REGISTRY NUMBER
COMMENTARY hide
85130-33-2
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ORGANISM
COMMENTARY hide
LITERATURE
UNIPROT
SEQUENCE DB
SOURCE
V.P.I. 12708
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Manually annotated by BRENDA team
SUBSTRATE
PRODUCT                       
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate) hide
LITERATURE
(Substrate)
COMMENTARY
(Product) hide
LITERATURE
(Product)
Reversibility
r=reversible
ir=irreversible
?=not specified
3alpha-hydroxy-5beta-6-cholen-24-oic acid + reduced acceptor
lithocholic acid + ?
show the reaction diagram
chenodeoxycholate + reduced acceptor
?
show the reaction diagram
chenodeoxycholate + reduced acceptor
lithocholate + ?
show the reaction diagram
chenodeoxycholate + reduced acceptor
lithocholate + acceptor
show the reaction diagram
cholate + FADH2
deoxycholate + FAD + H2O
show the reaction diagram
cholate + reduced acceptor
?
show the reaction diagram
cholate + reduced acceptor
deoxycholate + ?
show the reaction diagram
cholate + reduced acceptor
deoxycholate + acceptor
show the reaction diagram
ursodeoxycholate + reduced acceptor
?
show the reaction diagram
COFACTOR
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
NAD+
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specific activity increases 4-fold to 6-fold with either cholic acid or chenodeoxycholic acid as substrate in presence of NAD+. NAD+ stimulates 7alpha-dehydroxylation activity without any detectable reduction. Km: 0.13 mM (rection with cholate), 0.06 mM (reaction with chenodexycholate)
INHIBITORS
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
3alpha,7alpha-dihydroxy-7beta-methyl-5beta-cholan-24-oic acid
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0.05 mM, 66% inhibition
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3alpha,7beta-dihydroxy-7alpha-methyl-5beta-cholan-24-oic acid
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0.05 mM, 12% inhibition
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chenodeoxycholate
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substrate inhibition above 0.05 mM
NADPH
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0.5 mM, 62% inhibition of 7alpha-dehydroxylation of cholic acid, 42% inhibition of 7alpha-dehydroxylation of deoxycholic acid
additional information
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the enzyme is not inhibited in the presence of 7xi-methyl-lithocholic acid and ursodeoxycholylsarcosine
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ACTIVATING COMPOUND
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
FADH2
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stimulates reduction when added to reaction mixtures containing NAD+
FMNH2
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stimulates reduction when added to reaction mixtures containing NAD+
NADH
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stimulates 30-50% at low concentrations (below 0.15 mM). 7-Dehydroxylase activity is modulated by the molar ratio of NAD+ to NADH with maximal activity at a NAD+ mole fraction of 0.75 to 0.85
KM VALUE [mM]
SUBSTRATE
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
0.025
cholate
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pH 7.5, 37°C
pH OPTIMUM
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
7
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pH optimum of 7alpha-dehydroxylase activity in whole cells and cell extracts
TEMPERATURE OPTIMUM
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
PDB
SCOP
CATH
ORGANISM
UNIPROT
Clostridium scindens (strain JCM 10418 / VPI 12708)
Clostridium scindens (strain JCM 10418 / VPI 12708)
MOLECULAR WEIGHT
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
114000
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gel filtration
SUBUNITS
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
Purification/COMMENTARY
ORGANISM
UNIPROT
LITERATURE
Cloned/COMMENTARY
ORGANISM
UNIPROT
LITERATURE
expression in Escherichia coli
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EXPRESSION
ORGANISM
UNIPROT
LITERATURE
the enzyme is induced 90fold by cholic acid in cultures of Eubacterium sp. VPI 12708
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the enzyme is induced 90fold by cholic acid in cultures of Eubacterium sp. VPI 12708; the induction of 7alpha-dehydroxylase activity is highly specific requiring a free C-24-carboxyl group and an unhindered 7alpha-hydroxy group on the B ring of the steroid nucleus
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the induction of 7alpha-dehydroxylase activity is highly specific requiring a free C-24-carboxyl group and an unhindered 7alpha-hydroxy group on the B ring of the steroid nucleus
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