The Enzyme Database

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EC 1.14.13.98      
Transferred entry: cholesterol 24-hydroxylase. Now EC 1.14.14.25, cholesterol 24-hydroxylase
[EC 1.14.13.98 created 2005, deleted 2016]
 
 
EC 1.14.14.25     
Accepted name: cholesterol 24-hydroxylase
Reaction: cholesterol + [reduced NADPH—hemoprotein reductase] + O2 = (24S)-cholest-5-ene-3β,24-diol + [oxidized NADPH—hemoprotein reductase] + H2O
For diagram of cholic acid biosynthesis (sidechain), click here
Glossary: cholesterol = cholest-5-en-3β-ol
(24S)-24-hydroxycholesterol = (24S)-cholest-5-ene-3β,24-diol
Other name(s): cholesterol 24-monooxygenase; CYP46; CYP46A1; cholesterol 24S-hydroxylase; cytochrome P450 46A1
Systematic name: cholesterol,NADPH—hemoprotein reductase:oxygen oxidoreductase (24-hydroxylating)
Comments: A P-450 heme-thiolate protein. 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 enzymic degradation of cholesterol in the brain as hydroxycholesterol can pass the blood—brain barrier whereas cholesterol cannot [3]. The direct electron donor to the enzyme is EC 1.6.2.4, NADPH—hemoprotein reductase [3].
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 50812-30-1, 213327-78-7
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. [DOI] [PMID: 10377398]
2.  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. [DOI] [PMID: 11698143]
3.  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. [DOI] [PMID: 14640697]
4.  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. [DOI] [PMID: 12686551]
5.  Russell, D.W. The enzymes, regulation, and genetics of bile acid synthesis. Annu. Rev. Biochem. 72 (2003) 137–174. [DOI] [PMID: 12543708]
[EC 1.14.14.25 created 2005 as EC 1.14.13.98, transferred 2016 to EC 1.14.14.25]
 
 
EC 1.14.14.26     
Accepted name: 24-hydroxycholesterol 7α-hydroxylase
Reaction: (24S)-cholest-5-ene-3β,24-diol + [reduced NADPH—hemoprotein reductase] + O2 = (24S)-cholest-5-ene-3β,7α,24-triol + [oxidized NADPH—hemoprotein reductase] + H2O
For diagram of cholesterol catabolism (rings a, B and c), click here
Glossary: (24S)-cholest-5-ene-3β,24-diol = (24S)-24-hydroxycholesterol
Other name(s): 24-hydroxycholesterol 7α-monooxygenase; CYP39A1; CYP39A1 oxysterol 7α-hydroxylase
Systematic name: (24S)-cholest-5-ene-3β,24-diol,NADPH—hemoprotein reductase:oxygen oxidoreductase (7α-hydroxylating)
Comments: A P-450 heme-thiolate protein that is found in liver microsomes and in ciliary non-pigmented epithelium [2]. The enzyme is specific for (24S)-cholest-5-ene-3β,24-diol, which is formed mostly in the brain by EC 1.14.14.25, cholesterol 24-hydroxylase. The direct electron donor to the enzyme is EC 1.6.2.4, NADPH—hemoprotein reductase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 288309-90-0
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. [DOI] [PMID: 10748047]
2.  Ikeda, H., Ueda, M., Ikeda, M., Kobayashi, H. and Honda, Y. Oxysterol 7alpha-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. [DOI] [PMID: 12543708]
[EC 1.14.14.26 created 2005 as EC 1.14.13.99, transferred 2016 to EC 1.14.14.26]
 
 


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