ExplorEnz: EC 1.14.14.25

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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, PDB, 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]