Transferred entry: taurochenodeoxycholate 6α-hydroxylase. Now EC, taurochenodeoxycholate 6α-hydroxylase
[EC created 2005, deleted 2018]
Transferred entry: 1,8-cineole 2-exo-monooxygenase. Now EC, 1,8-cineole 2-exo-monooxygenase
[EC created 2012, deleted 2017]
Accepted name: 1,8-cineole 2-exo-monooxygenase
Reaction: 1,8-cineole + [reduced NADPH—hemoprotein reductase] + O2 = 2-exo-hydroxy-1,8-cineole + [oxidized NADPH—hemoprotein reductase] + H2O
Glossary: 1,8-cineole = 1,3,3-trimethyl-2-oxabicyclo[2.2.2]octane
2-exo-hydroxy-1,8-cineole = (1R,4S,6S)-1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-6-ol
Other name(s): CYP3A4
Systematic name: 1,8-cineole,[reduced NADPH—hemoprotein reductase]:oxygen oxidoreductase (2-exo-hydroxylating)
Comments: A cytochrome P-450 (heme-thiolate) protein. The mammalian enzyme, expressed in liver microsomes, performs a variety of oxidation reactions of structurally unrelated compounds, including steroids, fatty acids, and xenobiotics. cf. EC, quinine 3-monooxygenase, EC, taurochenodeoxycholate 6-hydroxylase and EC, albendazole monooxygenase (sulfoxide-forming).
1.  Miyazawa, M., Shindo, M. and Shimada, T. Oxidation of 1,8-cineole, the monoterpene cyclic ether originated from Eucalyptus polybractea, by cytochrome P450 3A enzymes in rat and human liver microsomes. Drug Metab. Dispos. 29 (2001) 200–205. [PMID: 11159812]
2.  Miyazawa, M. and Shindo, M. Biotransformation of 1,8-cineole by human liver microsomes. Nat. Prod. Lett. 15 (2001) 49–53. [PMID: 11547423]
3.  Miyazawa, M., Shindo, M. and Shimada, T. Roles of cytochrome P450 3A enzymes in the 2-hydroxylation of 1,4-cineole, a monoterpene cyclic ether, by rat and human liver microsomes. Xenobiotica 31 (2001) 713–723. [PMID: 11695850]
[EC created 2012 as EC, transferred 2017 to EC, modified 2018]
Accepted name: taurochenodeoxycholate 6α-hydroxylase
Reaction: (1) taurochenodeoxycholate + [reduced NADPH—hemoprotein reductase] + O2 = taurohyocholate + [oxidized NADPH—hemoprotein reductase] + H2O
(2) lithocholate + [reduced NADPH—hemoprotein reductase] + O2 = hyodeoxycholate + [oxidized NADPH—hemoprotein reductase] + H2O
Glossary: taurochenodeoxycholic acid = N-(3α,7α-dihydroxy-5β-cholan-24-oyl)taurine
taurohyocholic acid = N-(3α,6α,7α-trihydroxy-5β-cholan-24-oyl)taurine
hyodeoxycholate = 3α,6α-dihydroxy-5β-cholan-24-oate
lithocholate = 3α-hydroxy-5β-cholan-24-oate
Other name(s): CYP3A4; CYP4A21; taurochenodeoxycholate 6α-monooxygenase
Systematic name: taurochenodeoxycholate,[reduced NADPH—hemoprotein reductase]:oxygen oxidoreductase (6α-hydroxylating)
Comments: A cytochrome P-450 (heme-thiolate) protein. Requires cytochrome b5 for maximal activity. Acts on taurochenodeoxycholate, taurodeoxycholate and less readily on lithocholate and chenodeoxycholate. In adult pig (Sus scrofa), hyocholic acid replaces cholic acid as a primary bile acid [5].
1.  Araya, Z. and Wikvall, K. 6α-Hydroxylation of taurochenodeoxycholic acid and lithocholic acid by CYP3A4 in human liver microsomes. Biochim. Biophys. Acta 1438 (1999) 47–54. [PMID: 10216279]
2.  Araya, Z., Hellman, U. and Hansson, R. Characterisation of taurochenodeoxycholic acid 6α-hydroxylase from pig liver microsomes. Eur. J. Biochem. 231 (1995) 855–861. [PMID: 7649186]
3.  Kramer, W., Sauber, K., Baringhaus, K.H., Kurz, M., Stengelin, S., Lange, G., Corsiero, D., Girbig, F., Konig, W. and Weyland, C. Identification of the bile acid-binding site of the ileal lipid-binding protein by photoaffinity labeling, matrix-assisted laser desorption ionization-mass spectrometry, and NMR structure. J. Biol. Chem. 276 (2001) 7291–7301. [PMID: 11069906]
4.  Lundell, K., Hansson, R. and Wikvall, K. Cloning and expression of a pig liver taurochenodeoxycholic acid 6α-hydroxylase (CYP4A21): a novel member of the CYP4A subfamily. J. Biol. Chem. 276 (2001) 9606–9612. [PMID: 11113117]
5.  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]
6.  Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137–174. [PMID: 12543708]
[EC created 2005 asEC, transferred 2018 to EC]
Accepted name: 5β-cholestane-3α,7α-diol 12α-hydroxylase
Reaction: (1) 5β-cholestane-3α,7α-diol + [reduced NADPH—hemoprotein reductase] + O2 = 5β-cholestane-3α,7α,12α-triol + [oxidized NADPH—hemoprotein reductase] + H2O
(2) 7α-hydroxycholest-4-en-3-one + [reduced NADPH—hemoprotein reductase] + O2 = 7α,12α-dihydroxycholest-4-en-3-one + [oxidized NADPH—hemoprotein reductase] + H2O
(3) chenodeoxycholate + [reduced NADPH—hemoprotein reductase] + O2 = cholate + [oxidized NADPH—hemoprotein reductase] + H2O
Glossary: chenodeoxycholate = 3α,7α-dihydroxy-5β-cholan-24-oate
cholate = 3α,7α-12α-trihydroxy-5β-cholan-24-oate
Other name(s): 5β-cholestane-3α,7α-diol 12α-monooxygenase; sterol 12α-hydroxylase (ambiguous); CYP8B1; cytochrome P450 8B1; 7α-hydroxycholest-4-en-3-one 12α-hydroxylase; 7α-hydroxy-4-cholesten-3-one 12α-monooxygenase; chenodeoxycholate 12α monooxygenase
Systematic name: 5β-cholestane-3α,7α-diol,[reduced NADPH—hemoprotein reductase]:oxygen oxidoreductase (12α-hydroxylating)
Comments: A cytochrome P-450 (heme-thiolate) protein found in mammals. This is the key enzyme in the biosynthesis of the bile acid cholate. The enzyme can also hydroxylate 5β-cholestane-3α,7α-diol at the 25 and 26 position, but to a lesser extent [2].
1.  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]
2.  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]
3.  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]
4.  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]
5.  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]
6.  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]
7.  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 4alpha. Biochim. Biophys. Acta 1583 (2002) 63–73. [PMID: 12069850]
8.  Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137–174. [PMID: 12543708]
9.  Fan, L., Joseph, J.F., Durairaj, P., Parr, M.K. and Bureik, M. Conversion of chenodeoxycholic acid to cholic acid by human CYP8B1. Biol. Chem. 400 (2019) 625–628. [PMID: 30465713]
[EC created 2005 as EC, transferred 2018 to EC (EC created 2005 as EC, transferred 2015 to EC, incorporated 2020) , modified 2020]
Transferred entry: bile-acid 7α-dehydroxylase. Now EC, bile-acid 7α-dehydroxylase. It is now known that FAD is the acceptor and not NAD+ as was thought previously
[EC created 2005, deleted 2006]
Deleted entry: bile-acid 7α-dehydroxylase. Now known to be catalyzed by multiple enzymes.
[EC created 2005 as EC, transferred 2006 to EC, transferred 2014 to EC, deleted 2016]
Transferred entry: bile-acid 7α-dehydroxylase. Now classified as EC, bile-acid 7α-dehydroxylase.
[EC created 2005 as EC, transferred 2006 to EC, deleted 2014]
Accepted name: bile-salt sulfotransferase
Reaction: (1) 3′-phosphoadenylyl sulfate + glycolithocholate = adenosine 3′,5′-bisphosphate + glycolithocholate 3-sulfate
(2) 3′-phosphoadenylyl sulfate + taurolithocholate = adenosine 3′,5′-bisphosphate + taurolithocholate sulfate
Glossary: glycolithocholate 3-sulfate = N-(3α-sulfooxy-5β-cholan-24-oyl)glycine
Other name(s): BAST I; bile acid:3′-phosphoadenosine-5′-phosphosulfate sulfotransferase; bile salt:3′phosphoadenosine-5′-phosphosulfate:sulfotransferase; bile acid sulfotransferase I; glycolithocholate sulfotransferase; 3′-phosphoadenylyl-sulfate:glycolithocholate sulfotransferase
Systematic name: 3′-phosphoadenylyl-sulfate:glycolithocholate sulfonotransferase
Comments: The formation of sulfate esters of bile acids is an essential step in the prevention of toxicity by monohydroxy bile acids in many species [3]. This enzyme is both a bile salt and a 3-hydroxysteroid sulfotransferase. In addition to the 5β-bile acid glycolithocholate, deoxycholate, 3β-hydroxy-5-cholenoate and dehydroepiandrosterone (3β-hydroxyandrost-5-en-17-one) also act as substrates [see also EC (alcohol sulfotransferase) and EC (glycochenodeoxycholate sulfotransferase)]. May be identical to EC [3].
1.  Chen, L.-J., Bolt, R.J. and Admirand, W.H. Enzymatic sulfation of bile salts. Partial purification and characterization of an enzyme from rat liver that catalyzes the sulfation of bile salts. Biochim. Biophys. Acta 480 (1977) 219–227. [PMID: 831833]
2.  Barnes, S., Waldrop, R., Crenshaw, J., King, R.J. and Taylor, K.B. Evidence for an ordered reaction mechanism for bile salt: 3′phosphoadenosine-5′-phosphosulfate: sulfotransferase from rhesus monkey liver that catalyzes the sulfation of the hepatotoxin glycolithocholate. J. Lipid Res. 27 (1986) 1111–1123. [PMID: 3470420]
3.  Barnes, S., Buchina, E.S., King, R.J., McBurnett, T. and Taylor, K.B. Bile acid sulfotransferase I from rat liver sulfates bile acids and 3-hydroxy steroids: purification, N-terminal amino acid sequence, and kinetic properties. J. Lipid Res. 30 (1989) 529–540. [PMID: 2754334]
4.  Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137–174. [PMID: 12543708]
[EC created 1978, modified 2005]
Accepted name: glycochenodeoxycholate sulfotransferase
Reaction: 3′-phosphoadenylyl sulfate + glycochenodeoxycholate = adenosine 3′,5′-bisphosphate + glycochenodeoxycholate 7-sulfate
Glossary: 3′-phosphoadenylyl sulfate = PAPS
glycochenodeoxycholate 7-sulfate = N-(3α-hydroxy-7α-sulfooxy-5β-cholan-24-oyl)glycine
Other name(s): bile acid:3′-phosphoadenosine-5′-phosphosulfate sulfotransferase; bile acid:PAPS:sulfotransferase; BAST; 3′-phosphoadenylyl-sulfate:glycochenodeoxycholate 7-sulfotransferase
Systematic name: 3′-phosphoadenylyl-sulfate:glycochenodeoxycholate 7-sulfonotransferase
Comments: The enzyme specifically sulfates glycochenodeoxycholate at the 7α-position (see also EC bile-salt sulfotransferase). The monohydroxy bile acids glycolithocholate, chenodeoxycholate and ursodeoxycholate act as inhibitors.
1.  Barnes, S., Burhol, P.G., Zander, R., Haggstrom, G., Settine, R.L. and Hirschowitz, B.I. Enzymatic sulfation of glycochenodeoxycholic acid by tissue fractions from adult hamsters. J. Lipid Res. 20 (1979) 952–959. [PMID: 533830]
2.  Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137–174. [PMID: 12543708]
[EC created 2005]
Accepted name: chenodeoxycholoyltaurine hydrolase
Reaction: chenodeoxycholoyltaurine + H2O = chenodeoxycholate + taurine
Glossary: chenodeoxycholate = 3α,7α-dihydroxy-5β-cholan-24-oate
Systematic name: chenodeoxycholoyltaurine amidohydrolase
Comments: Some other taurine conjugates are hydrolysed, but not glycine conjugates of bile acids.
1.  Kawamoto, K., Horibe, I. and Uchida, K. Purification and characterization of a new hydrolase for conjugated bile acids, chenodeoxycholyltaurine hydrolase, from Bacteroides vulgatus. J. Biochem. (Tokyo) 106 (1989) 1049–1053. [PMID: 2628421]
[EC created 1992]
Accepted name: cholate—CoA ligase
Reaction: (1) ATP + cholate + CoA = AMP + diphosphate + choloyl-CoA
(2) ATP + (25R)-3α,7α,12α-trihydroxy-5β-cholestan-26-oate + CoA = AMP + diphosphate + (25R)-3α,7α,12α-trihydroxy-5β-cholestanoyl-CoA
Glossary: cholate = 3α,7α,12α-trihydroxy-5β-cholan-24-oate
trihydroxycoprostanoate = 3α,7α,12α-trihydroxy-5β-cholestan-26-oate
Other name(s): BAL; bile acid CoA ligase; bile acid coenzyme A ligase; choloyl-CoA synthetase; choloyl coenzyme A synthetase; cholic thiokinase; cholate thiokinase; cholic acid:CoA ligase; 3α,7α,12α-trihydroxy-5β-cholestanoyl coenzyme A synthetase; 3α,7α,12α-trihydroxy-5β-cholestanoate-CoA ligase; 3α,7α,12α-trihydroxy-5β-cholestanoate-CoA synthetase; THCA-CoA ligase; 3α,7α,12α-trihydroxy-5β-cholestanate—CoA ligase; 3α,7α,12α-trihydroxy-5β-cholestanate:CoA ligase (AMP-forming); cholyl-CoA synthetase; trihydroxycoprostanoyl-CoA synthetase
Systematic name: cholate:CoA ligase (AMP-forming)
Comments: Requires Mg2+ for activity. The mammalian enzyme is membrane-bound and catalyses the first step in the conjugation of bile acids with amino acids, converting bile acids into their acyl-CoA thioesters. Chenodeoxycholate, deoxycholate, lithocholate and trihydroxycoprostanoate can also act as substrates [7]. The bacterial enzyme is soluble and participates in an anaerobic bile acid 7 α-dehydroxylation pathway [5].
1.  Elliott, W.H. The enzymic activation of cholic acid by guinea-pig-liver microsomes. Biochem. J. 62 (1956) 427–433. [PMID: 13303991]
2.  Elliott, W.H. The breakdown of adenosine triphosphate accompanying cholic acid activation by guinea-pig liver microsomes. Biochem. J. 65 (1957) 315–321. [PMID: 13403911]
3.  Prydz, K., Kase, B.F., Björkhem, I. and Pedersen, J.I. Subcellular localization of 3α,7α-dihydroxy- and 3α,7α,12α-trihydroxy-5β-cholestanoyl-coenzyme A ligase(s) in rat liver. J. Lipid Res. 29 (1988) 997–1004. [PMID: 3183523]
4.  Schepers, L., Casteels, M., Verheyden, K., Parmentier, G., Asselberghs, S., Eyssen, H.J. and Mannaerts, G.P. Subcellular distribution and characteristics of trihydroxycoprostanoyl-CoA synthetase in rat liver. Biochem. J. 257 (1989) 221–229. [PMID: 2521999]
5.  Mallonee, D.H., Adams, J.L. and Hylemon, P.B. The bile acid-inducible baiB gene from Eubacterium sp. strain VPI 12708 encodes a bile acid-coenzyme A ligase. J. Bacteriol. 174 (1992) 2065–2071. [PMID: 1551828]
6.  Wheeler, J.B., Shaw, D.R. and Barnes, S. Purification and characterization of a rat liver bile acid coenzyme A ligase from rat liver microsomes. Arch. Biochem. Biophys. 348 (1997) 15–24. [PMID: 9390170]
7.  Falany, C.N., Xie, X., Wheeler, J.B., Wang, J., Smith, M., He, D. and Barnes, S. Molecular cloning and expression of rat liver bile acid CoA ligase. J. Lipid Res. 43 (2002) 2062–2071. [PMID: 12454267]
[EC created 1961 (EC created 1992, incorporated 2005), modified 2005]