IUBMB Enzyme Nomenclature


Accepted name: cholest-4-en-3-one 26-monooxygenase [(25S)-3-oxocholest-4-en-26-oate forming]

Reaction: cholest-4-en-3-one + 3 NADH + 3 H+ + 3 O2 = (25S)-3-oxocholest-4-en-26-oate + 3 NAD+ + 4 H2O (overall reaction)
(1a) cholest-4-en-3-one + NADH + H+ + O2 = (25S)-26-hydroxycholest-4-en-3-one + NAD+ + H2O
(1b) (25S)-26-hydroxycholest-4-en-3-one + NADH + H+ + O2 = (25S)-26-oxocholest-4-en-3-one + NAD+ + 2 H2O
(1c) (25S)-26-oxocholest-4-en-3-one + NADH + H+ + O2 = (25S)-3-oxocholest-4-en-26-oate + NAD+ + H2O

Other name(s): CYP125; CYP125A1; cholest-4-en-3-one 27-monooxygenase (misleading); cholest-4-en-3-one,NADH:oxygen oxidoreductase (26-hydroxylating); cholest-4-en-3-one 26-monooxygenase (ambiguous)

Systematic name: cholest-4-en-3-one,NADH:oxygen oxidoreductase [(25S)-3-oxocholest-4-en-26-oate forming]

Comments: This enzyme, found in several bacterial pathogens, is involved in degradation of the host's cholesterol. It catalyses the hydroxylation of the C-26 carbon, followed by oxidation of the alcohol to the carboxylic acid via the aldehyde intermediate, initiating the degradation of the alkyl side-chain of cholesterol [4]. The products are exclusively in the (25S) configuration. It is a two-component system consisting of a P-450 (heme thiolate) oxygenase (Cyp125) and a ferredoxin reductase (most likely KshB, which is also a part of EC , 3-ketosteroid 9α-monooxygenase). The enzyme also accepts cholesterol as a substrate. cf. EC, cholest-4-en-3-one 27-monooxygenase.

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:


1. Rosloniec, K.Z., Wilbrink, M.H., Capyk, J.K., Mohn, W.W., Ostendorf, M., van der Geize, R., Dijkhuizen, L. and Eltis, L.D. Cytochrome P450 125 (CYP125) catalyses C26-hydroxylation to initiate sterol side-chain degradation in Rhodococcus jostii RHA1. Mol. Microbiol. 74 (2009) 1031-1043. [PMID: 19843222]

2. McLean, K.J., Lafite, P., Levy, C., Cheesman, M.R., Mast, N., Pikuleva, I.A., Leys, D. and Munro, A.W. The Structure of Mycobacterium tuberculosis CYP125: molecular basis for cholesterol binding in a P450 needed for host infection. J. Biol. Chem. 284 (2009) 35524-35533. [PMID: 19846552]

3. Capyk, J.K., Kalscheuer, R., Stewart, G.R., Liu, J., Kwon, H., Zhao, R., Okamoto, S., Jacobs, W.R., Jr., Eltis, L.D. and Mohn, W.W. Mycobacterial cytochrome P450 125 (cyp125) catalyzes the terminal hydroxylation of C27 steroids. J. Biol. Chem. 284 (2009) 35534-35542. [PMID: 19846551]

4. Ouellet, H., Guan, S., Johnston, J.B., Chow, E.D., Kells, P.M., Burlingame, A.L., Cox, J.S., Podust, L.M. and de Montellano, P.R. Mycobacterium tuberculosis CYP125A1, a steroid C27 monooxygenase that detoxifies intracellularly generated cholest-4-en-3-one. Mol. Microbiol. 77 (2010) 730-742. [PMID: 20545858]

[EC created 2012, modified 2016]

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