An asterisk before 'EC' indicates that this is an amendment to an existing enzyme rather than a new enzyme entry.
Common name: δ4-3-oxosteroid 5β-reductase
Reaction: (1) 5β-cholestan-3-one + NADP+ = cholest-4-en-3-one + NADPH + H+
(2) 17,21-dihydroxy-5β-pregnane-3,11,20-trione + NADP+ = cortisone + NADPH + H+
Glossary: cortisone = 17,21-dihydroxypregn-4-ene-3,11,20-trione
For diagram click here.
Other name(s): 3-oxo-δ4-steroid 5β-reductase; 5β-reductase; androstenedione 5β-reductase; cholestenone 5β-reductase; cortisone 5β-reductase; cortisone β-reductase; cortisone δ4-5β-reductase; steroid 5β-reductase; testosterone 5β-reductase; δ4-3-ketosteroid 5β-reductase; δ4-5β-reductase; δ4-hydrogenase; 4,5β-dihydrocortisone:NADP+ δ4-oxidoreductase; 3-oxo-5β-steroid:NADP+ δ4-oxidoreductase
Systematic name: 5β-cholestan-3-one:NADP+ 4,5-oxidoreductase
Comments: The enzyme from human efficiently catalyses the reduction of progesterone, androstenedione, 17α-hydroxyprogesterone and testosterone to 5β-reduced metabolites; it can also act on aldosterone, corticosterone and cortisol, but to a lesser extent [8]. The bile acid intermediates 7α,12α-dihydroxy-4-cholesten-3-one and 7α-hydroxy-4-cholesten-3-one can also act as substrates [9].
Links to other databases: BRENDA, EXPASY, KEGG, ERGO, CAS registry number: 9029-08-7 and 37255-35-9
References:
1. Forchielli, E. and Dorfman, R.I. Separation of δ4-5α- and δ4-5β-hydrogenases from rat liver homogenates. J. Biol. Chem. 223 (1956) 443-448. [PMID: 13376613]
2. Brown-Grant, K., Forchielli, E. and Dorfman, R.I. The δ4-hydrogenases of guinea pig adrenal gland. J. Biol. Chem. 235 (1960) 1317-1320. [PMID: 13805063]
3. Levy, H.R. and Talalay, P. Enzymatic introduction of double bonds into steroid ring A. J. Am. Chem. Soc. 79 (1957) 2658-2659.
4. Tomkins, G.M. The enzymatic reduction of δ4-3-ketosteroids. J. Biol. Chem. 225 (1957) 13-24. [PMID: 13416214]
5. Sugimoto, Y., Yoshida, M. and Tamaoki, B. Purification of 5β-reductase from hepatic cytosol fraction of chicken. J. Steroid Biochem. Mol. Biol. 37 (1990) 717-724. [PMID: 2278855]
6. Furuebisu, M., Deguchi, S. and Okuda, K. Identification of cortisone 5β-reductase as δ4-3-ketosteroid 5β-reductase. Biochim. Biophys. Acta 912 (1987) 110-114. [PMID: 3828348]
7. Okuda, A. and Okuda, K. Purification and characterization of δ4-3-ketosteroid 5β-reductase. J. Biol. Chem. 259 (1984) 7519-7524. [PMID: 6736016]
8. Charbonneau, A. and The, V.L. Genomic organization of a human 5β-reductase and its pseudogene and substrate selectivity of the expressed enzyme. Biochim. Biophys. Acta 1517 (2001) 228-235. [PMID: 11342103]
9. Kondo, K.H., Kai, M.H., Setoguchi, Y., Eggertsen, G., Sjöblom, P., Setoguchi, T., Okuda, K.I. and Björkhem, I. Cloning and expression of cDNA of human δ4-3-oxosteroid 5β-reductase and substrate specificity of the expressed enzyme. Eur. J. Biochem. 219 (1994) 357-363. [PMID: 7508385]
[EC 1.3.1.23 Deleted entry: cholestenone β-reductase. The enzyme is identical to EC 1.3.1.3, δ4-3-oxosteroid 5β-reductase. (EC 1.3.1.23 created 1972, deleted 2005)]
Common name: cholestanetriol 26-monooxygenase
Reaction: 5β-cholestane-3α,7α,12α-triol + NADPH + H+ + O2 = (25R)-5β-cholestane-3α,7α,12α,26-tetraol + NADP+ + H2O
For diagram 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,NADPH:oxygen oxidoreductase (26-hydroxylating)
Comments: Requires ferrodoxin. Acts on cholesterol, cholest-5-en-3β,7α-diol, 7α-hydroxycholest-4-en-3-one, 5β-cholestane-3α,7α-diol as well as 5β-cholestane-3α,7α,12α-triol. With cholesterol as well as 26-hydroxycholesterol, 24-hydroxy- and 25-hydroxycholesterol are also formed. With prolonged treatment, 26-hydroxycholesterol is converted into the corresponding 27-aldehyde and 27-oic acid.
Links to other databases: BRENDA, EXPASY, KEGG, ERGO, CAS registry number: 52227-77-7
References:
1. Okuda, K. and Hoshita, N. Oxidation of 5β-cholestane-3α,7α,12α-triol by rat-liver mitochondria. Biochim. Biophys. Acta 164 (1968) 381-388. [PMID: 4388637]
2. 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]
3. 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]
4. Usui, E., Noshiro, M. and Okuda, K. Molecular cloning of cDNA for vitamin D3 25-hydroxylase from rat liver mitochondria. FEBS Lett. 262 (1990) 135-138. [PMID: 2318307]
5. 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. [PMID: 10512735]
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., Puchkaev, A. and Björkhem, I. Putative helix F contributes to regioselectivity of hydroxylation in mitochondrial cytochrome P450 27A1. Biochemistry 40 (2001) 7621-7629. [PMID: 11412116]
Common name: lithocholate 6β-hydroxylase
Reaction: lithocholate + NADPH + H+ + O2 = 6β-hydroxylithocholate + NADP+ + H2O
For diagram click here.
Glossary: lithocholic acid = 3α-hydroxy-5β-cholan-26-oic acid
murideoxycholic acid = 3α,6β-dihydroxy-5β-cholan-26-oic acid
Other name(s): lithocholate 6β-monooxygenase; CYP3A10; 6β-hydroxylase; cytochrome P450 3A10/lithocholic acid 6β-hydroxylase
Systematic name: lithocholate,NADPH:oxygen oxidoreductase (6β-hydroxylating)
Comments: A heme-thiolate protein (P-450). Expression of the gene for this enzyme is 50-fold higher in male compared to female hamsters [1].
References:
1. Teixeira, J. and Gil, G. Cloning, expression, and regulation of lithocholic acid 6β-hydroxylase. J. Biol. Chem. 266 (1991) 21030-21036. [PMID: 1840595]
2. Chang, T.K., Teixeira, J., Gil, G. and Waxman, D.J. The lithocholic acid 6β-hydroxylase cytochrome P-450, CYP 3A10, is an active catalyst of steroid-hormone 6β-hydroxylation. Biochem. J. 291 (1993) 429-433. [PMID: 8484723]
3. Subramanian, A., Wang, J. and Gil, G. STAT 5 and NF-Y are involved in expression and growth hormone-mediated sexually dimorphic regulation of cytochrome P450 3A10/lithocholic acid 6β-hydroxylase. Nucleic Acids Res. 26 (1998) 2173-2178. [PMID: 9547277]
4. Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137-174. [PMID: 12543708]
Common name: 7α-hydroxycholest-4-en-3-one 12α-hydroxylase
Reaction: 7α-hydroxycholest-4-en-3-one + NADPH + H+ + O2 = 7α,12α-dihydroxycholest-4-en-3-one + NADP+ + H2O
For diagram 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,NADPH:oxygen oxidoreductase (12α-hydroxylating)
Comments: A heme-thiolate protein (P-450). Requires EC 1.6.2.4, NADPH—hemoprotein 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 [2].
References:
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]
Common name: 5β-cholestane-3α,7α-diol 12α-hydroxylase
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 [3]. The enzyme can also hydroxylate the substrate at the 25 and 26 position, but to a lesser extent [1].
References:
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]
Common name: taurochenodeoxycholate 6α-hydroxylase
Reaction: (1) taurochenodeoxycholate + NADPH + H+ + O2 = taurohyocholate + NADP+ + H2O
(2) lithocholate + NADPH + H+ + O2 = hyodeoxycholate + NADP+ + H2O
For diagram click here.
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-cholanoate
Other name(s): CYP3A4; CYP4A21; taurochenodeoxycholate 6α-monooxygenase
Systematic name: taurochenodeoxycholate,NADPH:oxygen oxidoreductase (6α-hydroxylating)
Comments: A heme-thiolate protein (P-450). 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].
References:
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]
Common name: cholesterol 24-hydroxylase
Reaction: cholesterol + NADPH + H+ + O2 = (24S)-24-hydroxycholesterol + NADP+ + H2O
For diagram click here.
Glossary: cholesterol = cholest-5-en-3β-ol
Other name(s): cholesterol 24-monooxygenase; CYP46; CYP46A1; cholesterol 24S-hydroxylase; cytochrome P450 46A1
Systematic name: cholesterol,NADPH:oxygen oxidoreductase (24-hydroxylating)
Comments: A heme-thiolate protein (P-450). The enzyme can also produce 25-hydroxycholesterol. In addition, it can further hydroxylate the product to 24,25-dihydroxycholesterol and 24,27-dihydroxycholesterol [2]. This reaction is the first step in the enzymatic degradation of cholesterol in the brain as hydroxycholesterol can pass the blood—brain barrier whereas cholesterol cannot [3].
References:
1. Lund, E.G., Guileyardo, J.M. and Russell, D.W. cDNA cloning of cholesterol 24-hydroxylase, a mediator of cholesterol homeostasis in the brain. Proc. Natl. Acad. Sci. USA 96 (1999) 7238-7243. [PMID: 10377398]
2. Mast, N., Norcross, R., Andersson, U., Shou, M., Nakayama, K., Bjorkhem, I. and Pikuleva, I.A. Broad substrate specificity of human cytochrome P450 46A1 which initiates cholesterol degradation in the brain. Biochemistry 42 (2003) 14284-14292. [PMID: 14640697]
3. Lund, E.G., Xie, C., Kotti, T., Turley, S.D., Dietschy, J.M. and Russell, D.W. Knockout of the cholesterol 24-hydroxylase gene in mice reveals a brain-specific mechanism of cholesterol turnover. J. Biol. Chem. 278 (2003) 22980-22988. [PMID: 12686551]
4. Bogdanovic, N., Bretillon, L., Lund, E.G., Diczfalusy, U., Lannfelt, L., Winblad, B., Russell, D.W. and Björkhem, I. On the turnover of brain cholesterol in patients with Alzheimer's disease. Abnormal induction of the cholesterol-catabolic enzyme CYP46 in glial cells. Neurosci. Lett. 314 (2001) 45-48. [PMID: 11698143]
5. Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137-174. [PMID: 12543708]
Common name: 24-hydroxycholesterol 7α-hydroxylase
Reaction: (24R)-cholest-5-ene-3β,24-diol + NADPH + H+ + O2 = (24R)-cholest-5-ene-3β,7α,24-triol + NADP+ + H2O
For diagram click here.
Other name(s): 24-hydroxycholesterol 7α-monooxygenase; CYP39A1; CYP39A1 oxysterol 7α-hydroxylase
Systematic name: (24R)-cholest-5-ene-3β,24-diol,NADPH:oxygen oxidoreductase (7α-hydroxylating)
Comments: A heme-thiolate protein (P-450) that is found in liver microsomes and in ciliary non-pigmented epithelium [2]. The enzyme is specific for (24R)-cholest-5-ene-3β,24-diol as substrate.
References:
1. Li-Hawkins, J., Lund, E.G., Bronson, A.D. and Russell, D.W. Expression cloning of an oxysterol 7α-hydroxylase selective for 24-hydroxycholesterol. J. Biol. Chem. 275 (2000) 16543-16549. [PMID: 10748047]
2. Ikeda, H., Ueda, M., Ikeda, M., Kobayashi, H. and Honda, Y. Oxysterol 7α-hydroxylase (CYP39A1) in the ciliary nonpigmented epithelium of bovine eye. Lab. Invest. 83 (2003) 349-355. [PMID: 12649335]
3. Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137-174. [PMID: 12543708]
Common name: 25-hydroxycholesterol 7α-hydroxylase
Reaction: (1) cholest-5-ene-3β,25-diol + NADPH + H+ + O2 = cholest-5-ene-3β,7α,25-triol + NADP+ + H2O
(2) cholest-5-ene-3β,27-diol + NADPH + H+ + O2 = cholest-5-ene-3β,7α,27-triol + NADP+ + H2O
For diagram click here.
Other name(s): 25-hydroxycholesterol 7α-monooxygenase; CYP7B1; CYP7B1 oxysterol 7α-hydroxylase
Systematic name: cholest-5-ene-3β,25-diol,NADPH:oxygen oxidoreductase (7α-hydroxylating)
Comments: A heme-thiolate protein (P-450). Unlike EC 1.14.13.99, 24-hydroxycholesterol 7α-monooxygenase, which is specific for its oxysterol substrate, this enzyme can also metabolize the oxysterols 24,25-epoxycholesterol, 22-hydroxycholesterol and 24-hydroxycholesterol, but to a lesser extent [2].
References:
1. Toll, A., Wikvall, K., Sudjana-Sugiaman, E., Kondo, K.H. and Björkhem, I. 7α hydroxylation of 25-hydroxycholesterol in liver microsomes. Evidence that the enzyme involved is different from cholesterol 7α-hydroxylase. Eur. J. Biochem. 224 (1994) 309-316. [PMID: 7925343]
2. Li-Hawkins, J., Lund, E.G., Bronson, A.D. and Russell, D.W. Expression cloning of an oxysterol 7α-hydroxylase selective for 24-hydroxycholesterol. J. Biol. Chem. 275 (2000) 16543-16549. [PMID: 10748047]
3. Ren, S., Marques, D., Redford, K., Hylemon, P.B., Gil, G., Vlahcevic, Z.R. and Pandak, W.M. Regulation of oxysterol 7α-hydroxylase (CYP7B1) in the rat. Metabolism 52 (2003) 636-642. [PMID: 12759897]
4. Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137-174. [PMID: 12543708]
Common name: cholesterol 25-hydroxylase
Reaction: cholesterol + AH2 + O2 = 25-hydroxycholesterol + A + H2O
For diagram click here.
Glossary: cholesterol = cholest-5-en-3β-ol
Other name(s): cholesterol 25-monooxygenase
Systematic name: cholesterol,hydrogen-donor:oxygen oxidoreductase (25-hydroxylating)
Comments: Unlike most other sterol hydroxylases, this enzyme is not a cytochrome P-450. Instead, it uses diiron cofactors to catalyse the hydroxylation of hydrophobic substrates [1]. The diiron cofactor can be either Fe-O-Fe or Fe-OH-Fe and is bound to the enzyme through interactions with clustered histidine or glutamate residues [4,5]. In cell cultures, this enzyme down-regulates cholesterol synthesis and the processing of sterol regulatory element binding proteins (SREBPs).
References:
1. Lund, E.G., Kerr, T.A., Sakai, J., Li, W.P. and Russell, D.W. cDNA cloning of mouse and human cholesterol 25-hydroxylases, polytopic membrane proteins that synthesize a potent oxysterol regulator of lipid metabolism. J. Biol. Chem. 273 (1998) 34316-34327. [PMID: 9852097]
2. Chen, J.J., Lukyanenko, Y. and Hutson, J.C. 25-Hydroxycholesterol is produced by testicular macrophages during the early postnatal period and influences differentiation of Leydig cells in vitro. Biol. Reprod. 66 (2002) 1336-1341. [PMID: 11967195]
3. Lukyanenko, Y., Chen, J.J. and Hutson, J.C. Testosterone regulates 25-hydroxycholesterol production in testicular macrophages. Biol. Reprod. 67 (2002) 1435-1438. [PMID: 12390873]
4. Fox, B.G., Shanklin, J., Ai, J., Loehr, T.M. and Sanders-Loehr, J. Resonance Raman evidence for an Fe-O-Fe center in stearoyl-ACP desaturase. Primary sequence identity with other diiron-oxo proteins. Biochemistry 33 (1994) 12776-12786. [PMID: 7947683]
5. Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137-174. [PMID: 12543708]
Common name: bile-acid 7α-dehydroxylase
Reaction: (1) deoxycholate + NAD+ + H2O = cholate + NADH + H+
(2) lithocholate + NAD+ + H2O = chenodeoxycholate + NADH + H+
For diagram click here.
Glossary: deoxycholic acid = 3α,12α-dihydroxy-5β-cholan-26-oic acid
Other name(s): cholate 7α-dehydroxylase; 7α-dehydroxylase; bile acid 7-dehydroxylase
Systematic name: deoxycholate:NAD+ oxidoreductase
Comments: This enzyme is highly specific for bile-acid substrates and requires a free C-24 carboxy group and an unhindered 7α-hydroxy group on the B-ring of the steroid nucleus for activity. May be regulated by the ratio of NAD+ to NADH [2].
References:
1. White, B.A., Cacciapuoti, A.F., Fricke, R.J., Whitehead, T.R., Mosbach, E.H. and Hylemon, P.B. Cofactor requirements for 7α-dehydroxylation of cholic and chenodeoxycholic acid in cell extracts of the intestinal anaerobic bacterium, Eubacterium species V.P.I. 12708. J. Lipid Res. 22 (1981) 891-898. [PMID: 7276750]
2. White, B.A., Paone, D.A., Cacciapuoti, A.F., Fricke, R.J., Mosbach, E.H. and Hylemon, P.B. Regulation of bile acid 7-dehydroxylase activity by NAD+ and NADH in cell extracts of Eubacterium species V.P.I. 12708. J. Lipid Res. 24 (1983) 20-27. [PMID: 6833878]
3. Coleman, J.P., White, W.B. and Hylemon, P.B. Molecular cloning of bile acid 7-dehydroxylase from Eubacterium sp. strain VPI 12708. J. Bacteriol. 169 (1987) 1516-1521. [PMID: 3549693]
4. Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137-174. [PMID: 12543708]
Common name: 3α,7α,12α-trihydroxy-5β-cholestanoyl-CoA 24-hydroxylase
Reaction: (25R)-3α,7α,12α-trihydroxy-5β-cholestan-26-oyl-CoA + H2O + acceptor = (24R,25R)-3α,7α,12α,24-tetrahydroxy-5β-cholestan-26-oyl-CoA + reduced acceptor
For diagram click here.
Other name(s): trihydroxycoprostanoyl-CoA oxidase; THC-CoA oxidase; THCA-CoA oxidase; 3α,7α,12α-trihydroxy-5β-cholestanoyl-CoA oxidase; 3α,7α,12α-trihydroxy-5β-cholestan-26-oate 24-hydroxylase
Systematic name: (25R)-3α,7α,12α-trihydroxy-5β-cholestan-26-oyl-CoA:acceptor 24-oxidoreductase (24R-hydroxylating)
Comments: Requires ATP. The reaction in mammals possibly involves dehydrogenation to give a 24(25)-double bond followed by hydration [1]. However, in amphibians such as the Oriental fire-bellied toad (Bombina orientalis), it is probable that the product is formed via direct hydroxylation of the saturated side chain of (25R)-3α,7α,12α-trihydroxy-5β-cholestan-26-oate and not via hydration of a 24(25) double bond [5]. In microsomes, the free acid is preferred to the coenzyme A ester, whereas in mitochondria, the coenzyme A ester is preferred to the free-acid form of the substrate [1].
References:
1. Gustafsson, J. Biosynthesis of cholic acid in rat liver. 24-Hydroxylation of 3α,7α,12α-trihydroxy-5β-cholestanoic acid. J. Biol. Chem. 250 (1975) 8243-8247. [PMID: 240854]
2. Schepers, L., Van Veldhoven, P.P., Casteels, M., Eyssen, H.J. and Mannaerts, G.P. Presence of three acyl-CoA oxidases in rat liver peroxisomes. An inducible fatty acyl-CoA oxidase, a noninducible fatty acyl-CoA oxidase, and a noninducible trihydroxycoprostanoyl-CoA oxidase. J. Biol. Chem. 265 (1990) 5242-5246. [PMID: 2156865]
3. Dieuaide-Noubhani, M., Novikov, D., Baumgart, E., Vanhooren, J.C., Fransen, M., Goethals, M., Vandekerckhove, J., Van Veldhoven, P.P. and Mannaerts, G.P. Further characterization of the peroxisomal 3-hydroxyacyl-CoA dehydrogenases from rat liver. Relationship between the different dehydrogenases and evidence that fatty acids and the C27 bile acids di- and tri-hydroxycoprostanic acids are metabolized by separate multifunctional proteins. Eur. J. Biochem. 240 (1996) 660-666. [PMID: 8856068]
4. Dieuaide-Noubhani, M., Novikov, D., Baumgart, E., Vanhooren, J.C., Fransen, M., Goethals, M., Vandekerckhove, J., Van Veldhoven, P.P. and Mannaerts, G.P. Erratum report. Further characterization of the peroxisomal 3-hydroxyacyl-CoA dehydrogenases from rat liver. Relationship between the different dehydrogenases and evidence that fatty acids and the C27 bile acids di- and tri-hydroxycoprostanic acids are metabolized by separate multifunctional proteins. Eur. J. Biochem. 243 (1997) 537. [PMID: 8856068]
5. Pedersen, J.I., Eggertsen, G., Hellman, U., Andersson, U. and Björkhem, I. Molecular cloning and expression of cDNA encoding 3α,7α,12α-trihydroxy-5β-cholestanoyl-CoA oxidase from rabbit liver. J. Biol. Chem. 272 (1997) 18481-18489. [PMID: 9218493]
6. Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137-174. [PMID: 12543708]
Common name: bile acid-CoA:amino acid N-acyltransferase
Reaction: choloyl-CoA + glycine = CoA + glycocholate
For diagram click here.
Other name(s): glycine—taurine N-acyltransferase; amino acid N-choloyltransferase; BAT; glycine N-choloyltransferase; BACAT; cholyl-CoA glycine-taurine N-acyltransferase; cholyl-CoA:taurine N-acyltransferase
Systematic name: choloyl-CoA:glycine N-choloyltransferase
Comments: Also acts on CoA derivatives of other bile acids. Taurine and 2-fluoro-β-alanine can act as substrates, but more slowly [4]. The enzyme can also conjugate fatty acids to glycine and can act as a very-long-chain acyl-CoA thioesterase [7]. Bile-acid—amino-acid conjugates serve as detergents in the gastrointestinal tract, solubilizing long chain fatty acids, mono- and diglycerides, fat-soluble vitamins and cholesterol [4]. This is the second enzyme in a two-step process leading to the conjugation of bile acids with amino acids; the first step is the conversion of bile acids into their acyl-CoA thioesters, which is catalysed by EC 6.2.1.7, cholate—CoA ligase.
Links to other databases: BRENDA, EXPASY, KEGG, ERGO, CAS registry number: 74506-32-4
References:
1. Czuba, B. and Vessey, D.A. Kinetic characterization of cholyl-CoA glycine-taurine N-acyltransferase from bovine liver. J. Biol. Chem. 255 (1980) 5296-5299. [PMID: 7372637]
2. Jordan, T.W., Lee, R. and Lim, W.C. Isoelectric focussing of soluble and particulate benzoyl-CoA and cholyl-CoA:amino acid N-acyltransferases from rat liver. Biochem. Int. 1 (1980) 325-330.
3. Vessey, D.A. The co-purification and common identity of cholyl CoA:glycine- and cholyl CoA:taurine-N-acyltransferase activities from bovine liver. J. Biol. Chem. 254 (1979) 2059-2063. [PMID: 422567]
4. Johnson, M.R., Barnes, S., Kwakye, J.B. and Diasio, R.B. Purification and characterization of bile acid-CoA:amino acid N-acyltransferase from human liver. J. Biol. Chem. 266 (1991) 10227-10233. [PMID: 2037576]
5. 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]
6. He, D., Barnes, S. and Falany, C.N. Rat liver bile acid CoA:amino acid N-acyltransferase: expression, characterization, and peroxisomal localization. J. Lipid Res. 44 (2003) 2242-2249. [PMID: 12951368]
7. O'Byrne, J., Hunt, M.C., Rai, D.K., Saeki, M. and Alexson, S.E. The human bile acid-CoA:amino acid N-acyltransferase functions in the conjugation of fatty acids to glycine. J. Biol. Chem. 278 (2003) 34237-34244. [PMID: 12810727]
Common name: propanoyl-CoA C-acyltransferase
Reaction: 3α,7α,12α-trihydroxy-5β-cholanoyl-CoA + propanoyl-CoA = CoA + 3α,7α,12α-trihydroxy-24-oxo-5β-cholestanoyl-CoA
For diagram click here.
Other name(s): peroxisomal thiolase 2; sterol carrier protein-χ; SCPχ; PTE-2 (ambiguous)
Systematic name: 3α,7α,12α-trihydroxy-5β-cholanoyl-CoA:propanoyl-CoA C-acyltransferase
Comments: Also acts on dihydroxy-5β-cholestanoyl-CoA and other branched chain acyl-CoA derivatives. The enzyme catalyses the penultimate step in the formation of bile acids. The bile acid moiety is transferred from the acyl-CoA thioester (RCO-SCoA) to either glycine or taurine (NH2R') by EC 2.3.1.65, bile acid-CoA:amino acid N-acyltransferase [4].
References:
1. Pedersen, J.I. and Gustafsson, J. Conversion of 3α,7α,12α-trihydroxy-5β-cholestanoic acid into cholic acid by rat liver peroxisomes. FEBS Lett. 121 (1980) 345-348. [PMID: 7461136]
2. Kase, F., Björkhem, I. and Pedersen, J.I. Formation of cholic acid from 3α,7α,12α-trihydroxy-5β-cholestanoic acid by rat liver peroxisomes. J. Lipid Res. 24 (1983) 1560-1567. [PMID: 6668450]
3. Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137-174. [PMID: 12543708]
4. Falany, C.N., Johnson, M.R., Barnes, S. and Diasio, R.B. Glycine and taurine conjugation of bile acids by a single enzyme. Molecular cloning and expression of human liver bile acid CoA:amino acid N-acyltransferase. J. Biol. Chem. 269 (1994) 19375-19379. [PMID: 8034703]
Common 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
For diagram click here or here.
Glossary: 3'-phosphoadenylyl sulfate (PAPS): nucleotide sulfate
glycolithocholate sulfate = N-(3α-sulfooxy-5β-cholan-26-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
Systematic name: 3'-phosphoadenylyl-sulfate:glycolithocholate sulfotransferase
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 2.8.2.2 (alcohol sulfotransferase) and EC 2.8.2.34 (glycochenodeoxycholate sulfotransferase)]. May be identical to EC 2.8.2.2 [3].
Links to other databases: BRENDA, EXPASY, KEGG, ERGO, CAS registry number: 65802-92-8
References:
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]
Common name: glycochenodeoxycholate sulfotransferase
Reaction: 3'-phosphoadenylyl sulfate + glycochenodeoxycholate = adenosine 3',5'-bisphosphate + glycochenodeoxycholate 7-sulfate
For diagram click here.
Glossary: 3'-phosphoadenylyl sulfate (PAPS): nucleotide sulfate
glycochenodeoxycholate 7-sulfate = N-(3α-hydroxy-7α-sulfooxy-5β-cholan-26-oyl)glycine
Other name(s): bile acid:3'-phosphoadenosine-5'-phosphosulfate sulfotransferase; bile acid:PAPS:sulfotransferase; BAST
Systematic name: 3'-phosphoadenylyl-sulfate:glycochenodeoxycholate 7-sulfotransferase
Comments: The enzyme specifically sulfates glycochenodeoxycholate at the 7α-position (see also EC 2.8.2.14 bile-salt sulfotransferase). The monohydroxy bile acids glycolithocholate, chenodeoxycholate and ursodeoxycholate act as inhibitors.
References:
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]
Common name: choloyl-CoA hydrolase
Reaction: choloyl-CoA + H2O = cholate + CoA
For diagram click here.
Other name(s): PTE-2 (ambiguous); choloyl-coenzyme A thioesterase; chenodeoxycholoyl-coenzyme A thioesterase; peroxisomal acyl-CoA thioesterase 2
Systematic name: choloyl-CoA hydrolase
Comments: Also acts on chenodeoxycholoyl-CoA and to a lesser extent on short- and medium- to long-chain acyl-CoAs, and other substrates, including trihydroxycoprostanoyl-CoA, hydroxymethylglutaryl-CoA and branched chain acyl-CoAs, all of which are present in peroxisomes. The enzyme is strongly inhibited by CoA and may be involved in controlling CoA levels in the peroxisome [1].
References:
1. Hunt, M.C., Solaas, K., Kase, B.F. and Alexson, S.E. Characterization of an acyl-coA thioesterase that functions as a major regulator of peroxisomal lipid metabolism. J. Biol. Chem. 277 (2002) 1128-1138. [PMID: 11673457]
2. Solaas, K., Sletta, R.J., Soreide, O. and Kase, B.F. Presence of choloyl- and chenodeoxycholoyl-coenzyme A thioesterase activity in human liver. Scand. J. Clin. Lab. Invest. 60 (2000) 91-102. [PMID: 10817395]
3. Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137-174. [PMID: 12543708]
Common name: 3α,7α,12α-trihydroxy-5β-cholest-24-enoyl-CoA hydratase
Reaction: (24R,25R)-3α,7α,12α,24-tetrahydroxy-5β-cholestanoyl-CoA = (24E)-3α,7α,12α-trihydroxy-5β-cholest-24-enoyl-CoA + H2O
For diagram click here.
Other name(s): 46 kDa hydratase 2
Systematic name: (24R,25R)-3α,7α,12α,24-tetrahydroxy-5β-cholestanoyl-CoA hydro-lyase
Comments: This enzyme forms part of the rat peroxisomal multifunctional enzyme perMFE-2, which also exhibits a dehydrogenase activity. The enzyme is involved in the β-oxidation of the cholesterol side chain in the cholic-acid-biosynthesis pathway.
References:
1. Qin, Y.M., Haapalainen, A.M., Conry, D., Cuebas, D.A., Hiltunen, J.K. and Novikov, D.K. Recombinant 2-enoyl-CoA hydratase derived from rat peroxisomal multifunctional enzyme 2: role of the hydratase reaction in bile acid synthesis. Biochem. J. 328 (1997) 377-382. [PMID: 9371691]
2. Xu, R. and Cuebas, D.A. The reactions catalyzed by the inducible bifunctional enzyme of rat liver peroxisomes cannot lead to the formation of bile acids. Biochem. Biophys. Res. Commun. 221 (1996) 271-278. [PMID: 8619845]
3. Kinoshita, T., Miyata, M., Ismail, S.M., Fujimoto, Y., Kakinuma, K., Kokawa, N.I. and Morisaki, M. Synthesis and determination of stereochemistry of four diastereoisomers at the C-24 and C-25 positions of 3α,7α,12α,24-tetrahydroxy-5β-cholestan-26-oic acid and cholic acid. Chem. Pharm. Bull. 36 (1988) 134-141.
4. Fujimoto, Y., Kinoshita, T., Oya, I., Kakinuma, K., Ismail, S.M., Sonoda, Y., Sato, Y. and Morisaki, M. Non-stereoselective conversion of the four diastereoisomers at the C-24 and C-25 positions of 3α,7α,12α,24-tetrahydroxy-5β-cholestan-26-oic acid and cholic acid. Chem. Pharm. Bull. 36 (1988) 142-145.
5. Kurosawa, T., Sato, M., Nakano, H., Fujiwara, M., Murai, T., Yoshimura, T. and Hashimoto, T. Conjugation reactions catalyzed by bifunctional proteins related to β-oxidation in bile acid biosynthesis. Steroids 66 (2001) 107-114. [PMID: 11146090]
6. Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137-174. [PMID: 12543708]
Common name: cholate—CoA ligase
Reaction: (1) ATP + cholate + CoA = AMP + diphosphate + choloyl-CoA
(2) ATP + 3α,7α,12α-trihydroxy-5β-cholestanoate + CoA = AMP + diphosphate + 3α,7α,12α-trihydroxy-5β-cholestanoyl-CoA
For diagram click here.
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. This membrane-bound enzyme catalyses the first step in the conjugation of bile acids with amino acids, converting bile acids into their acyl-CoA thioesters. The second step involves EC 2.3.1.65, bile acid-CoA:amino acid N-acyltransferase and converts the acyl-CoA thioester into the corresponding N-acyl amidate by conjugation with glycine or taurine [5]. Chenodeoxycholate, deoxycholate, lithocholate and trihydroxycoprostanoate can also act as substrates [6].
Links to other databases: BRENDA, EXPASY, KEGG, ERGO, CAS registry number: 9027-90-1 and 118732-04-0
References:
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. 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]
6. 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 6.2.1.29 Deleted entry: 3α,7α,12α-trihydroxy-5β-cholestanate—CoA ligase. The enzyme is identical to EC 6.2.1.7, cholate—CoA ligase (EC 6.2.1.29 created 1992, deleted 2005)]