Reaction: 5β-cholestane-3α,7α-diol + NADPH + H+ + O2 = 5β-cholestane-3α,7α,12α-triol + NADP+ + H2O
For diagram click here.
Other name(s): 5β-cholestane-3α,7α-diol 12α-monooxygenase; sterol 12α-hydroxylase (ambiguous); CYP8B1; cytochrome P450 8B1
Systematic name: 5β-cholestane-3α,7α-diol,NADPH:oxygen oxidoreductase (12α-hydroxylating)
Comments: A heme-thiolate protein (P-450). This is the key enzyme in the biosynthesis of the bile acid cholic acid (3α,7α,12α-trihydroxy-5β-cholanoic acid). The activity of this enzyme determines the biosynthetic ratio between cholic acid and chenodeoxycholic acid . The enzyme can also hydroxylate the substrate at the 25 and 26 position, but to a lesser extent .
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:
1. Hansson, R. and Wikvall, K. Hydroxylations in biosynthesis of bile acids. Cytochrome P-450 LM4 and 12α-hydroxylation of 5β-cholestane-3α,7α-diol. Eur. J. Biochem. 125 (1982) 423-429. [PMID: 6811268]
2. Hansson, R. and Wikvall, K. Hydroxylations in biosynthesis and metabolism of bile acids. Catalytic properties of different forms of cytochrome P-450. J. Biol. Chem. 255 (1980) 1643-1649. [PMID: 6766451]
3. Lundell, K. and Wikvall, K. Gene structure of pig sterol 12α-hydroxylase (CYP8B1) and expression in fetal liver: comparison with expression of taurochenodeoxycholic acid 6α-hydroxylase (CYP4A21). Biochim. Biophys. Acta 1634 (2003) 86-96. [PMID: 14643796]
4. del Castillo-Olivares, A. and Gil, G. α1-Fetoprotein transcription factor is required for the expression of sterol 12α-hydroxylase, the specific enzyme for cholic acid synthesis. Potential role in the bile acid-mediated regulation of gene transcription. J. Biol. Chem. 275 (2000) 17793-17799. [PMID: 10747975]
5. Yang, Y., Zhang, M., Eggertsen, G. and Chiang, J.Y. On the mechanism of bile acid inhibition of rat sterol 12α-hydroxylase gene (CYP8B1) transcription: roles of α-fetoprotein transcription factor and hepatocyte nuclear factor 4α. Biochim. Biophys. Acta 1583 (2002) 63-73. [PMID: 12069850]
6. Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137-174. [PMID: 12543708]