Reaction: 7α-hydroxycholest-4-en-3-one + 2 ferrocytochrome b5 + 2 H+ + O2 = 7α,12α-dihydroxycholest-4-en-3-one + 2 ferricytochrome b5 + + H2O
For diagram of reaction click here.
Other name(s): 7α-hydroxy-4-cholesten-3-one 12α-monooxygenase; CYP12; sterol 12α-hydroxylase (ambiguous); HCO 12α-hydroxylase
Systematic name: 7α-hydroxycholest-4-en-3-one,ferrocytochrome-b5:oxygen oxidoreductase (12α-hydroxylating)
Comments: A P-450 heme-thiolate protein. Requires EC 126.96.36.199, NADPHhemoprotein 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 .
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
1. Ishida, H., Noshiro, M., Okuda, K. and Coon, M.J. Purification and characterization of 7α-hydroxy-4-cholesten-3-one 12α-hydroxylase. J. Biol. Chem. 267 (1992) 21319-21323. [PMID: 1400444]
2. Eggertsen, G., Olin, M., Andersson, U., Ishida, H., Kubota, S., Hellman, U., Okuda, K.I. and Björkhem, I. Molecular cloning and expression of rabbit sterol 12α-hydroxylase. J. Biol. Chem. 271 (1996) 32269-32275. [PMID: 8943286]
3. Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137-174. [PMID: 12543708]