The Enzyme Database

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Accepted name: cholestanetriol 26-monooxygenase
Reaction: 5β-cholestane-3α,7α,12α-triol + 6 reduced adrenodoxin + 6 H+ + 3 O2 = (25R)-3α,7α,12α-trihydroxy-5β-cholestan-26-oate + 6 oxidized adrenodoxin + 4 H2O (overall reaction)
(1a) 5β-cholestane-3α,7α,12α-triol + 2 reduced adrenodoxin + 2 H+ + O2 = (25R)-5β-cholestane-3α,7α,12α,26-tetraol + 2 oxidized adrenodoxin + H2O
(1b) (25R)-5β-cholestane-3α,7α,12α,26-tetraol + 2 reduced adrenodoxin + 2 H+ + O2 = (25R)-3α,7α,12α-trihydroxy-5β-cholestan-26-al + 2 oxidized adrenodoxin + 2 H2O
(1c) (25R)-3α,7α,12α-trihydroxy-5β-cholestan-26-al + 2 reduced adrenodoxin + 2 H+ + O2 = (25R)-3α,7α,12α-trihydroxy-5β-cholestan-26-oate + 2 oxidized adrenodoxin + H2O
For diagram of cholic acid biosynthesis (sidechain), click here
Other name(s): 5β-cholestane-3α,7α,12α-triol 26-hydroxylase; 5β-cholestane-3α,7α,12α-triol hydroxylase; cholestanetriol 26-hydroxylase; sterol 27-hydroxylase; sterol 26-hydroxylase; cholesterol 27-hydroxylase; CYP27A; CYP27A1; cytochrome P450 27A1′
Systematic name: 5β-cholestane-3α,7α,12α-triol,adrenodoxin:oxygen oxidoreductase (26-hydroxylating)
Comments: This mitochondrial cytochrome P-450 enzyme requires adrenodoxin. It catalyses the first three sterol side chain oxidations in bile acid biosynthesis via the neutral (classic) pathway. Can also act on cholesterol, cholest-5-ene-3β,7α-diol, 7α-hydroxycholest-4-en-3-one, and 5β-cholestane-3α,7α-diol. The enzyme can also hydroxylate cholesterol at positions 24 and 25. The initial source of the electrons is NADPH, which transfers the electrons to the adrenodoxin via EC, adrenodoxin-NADP+ reductase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 52227-77-7
1.  Masui, T., Herman, R. and Staple, E. The oxidation of 5β-cholestane-3α,7α,12α,26-tetraol to 5β-cholestane-3α,7α,12α-triol-26-oic acid via 5β-cholestane-3α,7α,12α-triol-26-al by rat liver. Biochim. Biophys. Acta 117 (1966) 266–268. [DOI] [PMID: 5914340]
2.  Okuda, K. and Hoshita, N. Oxidation of 5β-cholestane-3α,7α,12α-triol by rat-liver mitochondria. Biochim. Biophys. Acta 164 (1968) 381–388. [DOI] [PMID: 4388637]
3.  Wikvall, K. Hydroxylations in biosynthesis of bile acids. Isolation of a cytochrome P-450 from rabbit liver mitochondria catalyzing 26-hydroxylation of C27-steroids. J. Biol. Chem. 259 (1984) 3800–3804. [PMID: 6423637]
4.  Andersson, S., Davis, D.L., Dahlbäck, H., Jörnvall, H. and Russell, D.W. Cloning, structure, and expression of the mitochondrial cytochrome P-450 sterol 26-hydroxylase, a bile acid biosynthetic enzyme. J. Biol. Chem. 264 (1989) 8222–8229. [PMID: 2722778]
5.  Dahlback, H. and Holmberg, I. Oxidation of 5β-cholestane-3α,7α,12α-triol into 3α,7α,12α-trihydroxy-5β-cholestanoic acid by cytochrome P-45026 from rabbit liver mitochondria. Biochem. Biophys. Res. Commun. 167 (1990) 391–395. [DOI] [PMID: 2322231]
6.  Holmberg-Betsholtz, I., Lund, E., Björkhem, I. and Wikvall, K. Sterol 27-hydroxylase in bile acid biosynthesis. Mechanism of oxidation of 5β-cholestane-3α,7α,12α,27-tetrol into 3α,7α,12α-trihydroxy-5β-cholestanoic acid. J. Biol. Chem. 268 (1993) 11079–11085. [PMID: 8496170]
7.  Pikuleva, I.A., Babiker, A., Waterman, M.R. and Bjorkhem, I. Activities of recombinant human cytochrome P450c27 (CYP27) which produce intermediates of alternative bile acid biosynthetic pathways. J. Biol. Chem. 273 (1998) 18153–18160. [DOI] [PMID: 9660774]
8.  Furster, C., Bergman, T. and Wikvall, K. Biochemical characterization of a truncated form of CYP27A purified from rabbit liver mitochondria. Biochem. Biophys. Res. Commun. 263 (1999) 663–666. [DOI] [PMID: 10512735]
9.  Pikuleva, I.A., Puchkaev, A. and Björkhem, I. Putative helix F contributes to regioselectivity of hydroxylation in mitochondrial cytochrome P450 27A1. Biochemistry 40 (2001) 7621–7629. [DOI] [PMID: 11412116]
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