MetaCyc Enzyme: 7α-hydroxycholest-4-en-3-one 12α-hydroxylase

Synonyms: CYP12

Species: Oryctolagus cuniculus

Subunit composition of 7α-hydroxycholest-4-en-3-one 12α-hydroxylase = [POR][CYP8B1]
         NADPH-cytochrome P450 reductase = POR (summary available)
         cytochrome P450 8B1 = CYP8B1 (summary available)

Gene-Reaction Schematic

Gene-Reaction Schematic

Created 15-Oct-2008 by Fulcher CA, SRI International

Enzymatic reaction of: 7α-hydroxycholest-4-en-3-one 12α-hydroxylase

Inferred from experiment

Synonyms: 7α-hydroxy-4-cholesten-3-one 12α-hydroxylase, sterol 12α-hydroxylase, 7α-hydroxy-4-cholesten-3-one 12α-monooxygenase, 7α-hydroxycholest-4-en-3-one,NADPH:oxygen oxidoreductase (12α-hydroxylating)

EC Number:

7α-hydroxycholest-4-en-3-one + 2 a ferrocytochrome b5 + 2 H+ + oxygen → 7α,12α-dihydroxycholest-4-en-3-one + 2 a ferricytochrome b5 + H2O

The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

In Pathways: bile acid biosynthesis, neutral pathway

This enzyme requires NADPH-cytochrome P450 reductase for its activity. It was assayed using the reductase, phospholipid and a NADPH regenerating system. Inclusion of cytochrome b5 enhanced the activity [Ishida92].

The level of this enzyme activity determines the relative amounts of cholate and chenodeoxycholate (or other species-specific bile acid) produced in the liver. The 12α hydroxylation leads to cholate biosynthesis (reviewed in [Russell03] and [Norlin07]).

This enzyme also catalyzes EC ( 5β-cholestane-3α,7α-diol + NAD(P)H + oxygen + H+ → 5β-cholestane-3α,7α,12α-triol + NAD(P)+ + H2O) and has broad substrate specificity, although 7α-hydroxycholest-4-en-3-one was the more efficient substrate. Recombinant enzyme was also demonstrated to have these activities [Andersson98].

Component enzyme of 7α-hydroxycholest-4-en-3-one 12α-hydroxylase : NADPH-cytochrome P450 reductase

Gene: POR Accession Number: G-10911 (MetaCyc)

Molecular Weight: 76.588 kD (from nucleotide sequence)

Molecular Weight: 77.0 kD (experimental) [Black82]

Unification Links: Protein Model Portal:P00389, SMR:P00389, UniProt:P00389

Relationship Links: InterPro:IN-FAMILY:IPR001094, InterPro:IN-FAMILY:IPR001433, InterPro:IN-FAMILY:IPR001709, InterPro:IN-FAMILY:IPR003097, InterPro:IN-FAMILY:IPR008254, InterPro:IN-FAMILY:IPR017927, InterPro:IN-FAMILY:IPR017938, InterPro:IN-FAMILY:IPR023173, InterPro:IN-FAMILY:IPR023208, InterPro:IN-FAMILY:IPR029039, Pfam:IN-FAMILY:PF00175, Pfam:IN-FAMILY:PF00258, Pfam:IN-FAMILY:PF00667, Prints:IN-FAMILY:PR00369, Prints:IN-FAMILY:PR00371, Prosite:IN-FAMILY:PS50902, Prosite:IN-FAMILY:PS51384

n oxidized hemoproteins + NADPH + H+ = n reduced hemoproteins + NADP+

The enzyme is believed to form a stable, 1:1 complex with cytochrome P450 (in [Black82]).

The native apparent molecular mass was determined by SDS-PAGE [Black82].

Subunit of 7α-hydroxycholest-4-en-3-one 12α-hydroxylase: cytochrome P450 8B1

Synonyms: CYPVIIIB1

Gene: CYP8B1 Accession Number: G-10912 (MetaCyc)

Locations: endoplasmic reticulum membrane

Molecular Weight: 57.494 kD (from nucleotide sequence)

Molecular Weight: 50.0 kD (experimental) [Ishida92]

GO Terms:
Cellular Component:
GO:0005789 - endoplasmic reticulum membrane [Ishida92]

Unification Links: Protein Model Portal:O02766, UniProt:O02766

Relationship Links: InterPro:IN-FAMILY:IPR001128, InterPro:IN-FAMILY:IPR002403, InterPro:IN-FAMILY:IPR024204, InterPro:IN-FAMILY:IPR030686, Pfam:IN-FAMILY:PF00067, Prints:IN-FAMILY:PR00465, Prosite:IN-FAMILY:PS00086

The apparent molecular mass was determined by SDS-PAGE [Ishida92].

The enzyme is liver-specific. The gene CYP8B1 encoding the enzyme is transcriptionally regulated (reviewed in [Norlin07] and [Russell03]).


Andersson98: Andersson U, Eggertsen G, Bjorkhem I (1998). "Rabbit liver contains one major sterol 12alpha-hydroxylase with broad substrate specificity." Biochim Biophys Acta 1389(2);150-4. PMID: 9461256

Black82: Black SD, Coon MJ (1982). "Structural features of liver microsomal NADPH-cytochrome P-450 reductase. Hydrophobic domain, hydrophilic domain, and connecting region." J Biol Chem 257(10);5929-38. PMID: 6802823

Ishida92: Ishida H, Noshiro M, Okuda K, Coon MJ (1992). "Purification and characterization of 7 alpha-hydroxy-4-cholesten-3-one 12 alpha-hydroxylase." J Biol Chem 267(30);21319-23. PMID: 1400444

Norlin07: Norlin M, Wikvall K (2007). "Enzymes in the conversion of cholesterol into bile acids." Curr Mol Med 7(2);199-218. PMID: 17346171

Russell03: Russell DW (2003). "The enzymes, regulation, and genetics of bile acid synthesis." Annu Rev Biochem 72;137-74. PMID: 12543708

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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