Information on EC 1.14.18.8 - 7alpha-hydroxycholest-4-en-3-one 12alpha-hydroxylase

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The enzyme appears in viruses and cellular organisms

EC NUMBER
COMMENTARY hide
1.14.18.8
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RECOMMENDED NAME
GeneOntology No.
7alpha-hydroxycholest-4-en-3-one 12alpha-hydroxylase
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REACTION
REACTION DIAGRAM
COMMENTARY hide
ORGANISM
UNIPROT
LITERATURE
7alpha-hydroxycholest-4-en-3-one + 2 ferrocytochrome b5 + 2 H+ + O2 = 7alpha,12alpha-dihydroxycholest-4-en-3-one + 2 ferricytochrome b5 + + H2O
show the reaction diagram
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REACTION TYPE
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
redox reaction
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PATHWAY
BRENDA Link
KEGG Link
MetaCyc Link
bile acid biosynthesis, neutral pathway
Primary bile acid biosynthesis
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Metabolic pathways
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SYSTEMATIC NAME
IUBMB Comments
7alpha-hydroxycholest-4-en-3-one,ferrocytochrome-b5:oxygen oxidoreductase (12alpha-hydroxylating)
A P-450 heme-thiolate protein. Requires EC 1.6.2.4, NADPH---hemoprotein reductase and cytochrome b5 for maximal activity. This enzyme is important in bile acid biosynthesis, being responsible for the balance between the formation of cholic acid and chenodeoxycholic acid [2].
CAS REGISTRY NUMBER
COMMENTARY hide
39369-22-7
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55963-45-6
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ORGANISM
COMMENTARY hide
LITERATURE
UNIPROT
SEQUENCE DB
SOURCE
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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
7alpha-hydroxycholest-4-en-3-one + NADH + H+ + O2
7alpha,12alpha-dihydroxycholest-4-en-3-one + NAD+ + H2O
show the reaction diagram
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reaction with NADH shows 15% of the activity with NADPH
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?
7alpha-hydroxycholest-4-en-3-one + NADPH + H+ + O2
7alpha,12alpha-dihydroxycholest-4-en-3-one + NADP+ + H2O
show the reaction diagram
NATURAL SUBSTRATES
NATURAL PRODUCTS
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate) hide
LITERATURE
(Substrate)
COMMENTARY
(Product) hide
LITERATURE
(Product)
REVERSIBILITY
r=reversible
ir=irreversible
?=not specified
7alpha-hydroxycholest-4-en-3-one + NADPH + H+ + O2
7alpha,12alpha-dihydroxycholest-4-en-3-one + NADP+ + H2O
show the reaction diagram
COFACTOR
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
cytochrome b5
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omission of cytochrome b5 resulted in 40% loss of activity
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cytochrome P-450
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cytochrome P450
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omission results in complete loss of activity
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NADH
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15% of the activity with NADPH
NADPH
INHIBITORS
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
5beta-cholestane-3alpha,7alpha,12alpha-triol
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0.066 mM, 62% inhibition
5beta-cholestane-3alpha,7alpha-diol
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0.066 mM, 30% inhibition
Emulgen 913
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0.1% w/v, complete inhibition
MgCl2
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1 mM, 10% inhibition
ACTIVATING COMPOUND
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
additional information
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NADPH-cytochrome P-450 reductase, EC 1.6.2.4, is required for maximal activity
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KM VALUE [mM]
SUBSTRATE
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
0.027
7alpha-hydroxycholest-4-en-3-one
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SPECIFIC ACTIVITY [µmol/min/mg]
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
0.000885
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liver microsome
pH OPTIMUM
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
pH RANGE
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
6 - 7.5
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pH 6.0: about 40% of maximal activity, pH 7.5: about 65% of maximal activity
SOURCE TISSUE
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
SOURCE
LOCALIZATION
ORGANISM
UNIPROT
COMMENTARY hide
GeneOntology No.
LITERATURE
SOURCE
MOLECULAR WEIGHT
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
56000
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non-denaturing PAGE
SUBUNITS
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
?
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x * 50000, SDS-PAGE
POSTTRANSLATIONAL MODIFICATION
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
additional information
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immunoblotting experiment show no correlation between the enzyme activity and the amount of protein, suggesting that post-translational modification may occur
GENERAL STABILITY
ORGANISM
UNIPROT
LITERATURE
stabilized at least 4 weeks under high buffer concentrations such as 300 mM phosphate buffer
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Purification/COMMENTARY
ORGANISM
UNIPROT
LITERATURE
Cloned/COMMENTARY
ORGANISM
UNIPROT
LITERATURE
expression in COS cells
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transfection of COS-M6 cells with the coding part of the cDNA
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EXPRESSION
ORGANISM
UNIPROT
LITERATURE
dexomethasone acutely induces hepatic mRNA levels of cholesterol 7alpha-hydrol Cyp6a1, cholesterol 27-hydrolase Cyp27, and in particular sterol 12alpha-hydrolase Cyp8b1. Neonatal dexomethasone administration leads to increased biliary lipid secretion, decreased Cyp8b1 mRNA expression and a 3fold higher Cyp7a1/Cyp8b1 mRNA ratio in rats at week 8
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in mice deficient for liver receptor homolog LRH-1, basal CYP8B1 mRNA levels are significantly decreased. CYP8B1 repression by farnesoid X receptor FXR is intact in mice deficient for LRH-1 in hepatocytes
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