IUBMB Enzyme Nomenclature

EC 1.14.18.9

Accepted name: methylsterol monooxygenase

Reaction: 4,4-dimethyl-5α-cholest-7-en-3β-ol + 6 ferrocytochrome b5 + 3 O2 + 6 H+ = 3β-hydroxy-4β-methyl-5α-cholest-7-ene-4α-carboxylate + 6 ferricytochrome b5 + 4 H2O (overall reaction)
(1a) 4,4-dimethyl-5α-cholest-7-en-3β-ol + 2 ferrocytochrome b5 + O2 + 2 H+ = 4β-hydroxymethyl-4α-methyl-5α-cholest-7-en-3β-ol + 2 ferricytochrome b5 + H2O
(1b) 4β-hydroxymethyl-4α-methyl-5α-cholest-7-en-3β-ol + 2 ferrocytochrome b5 + O2 + 2 H+ = 3β-hydroxy-4β-methyl-5α-cholest-7-ene-4α-carbaldehyde + 2 ferricytochrome b5 + 2 H2O
(1c) 3β-hydroxy-4β-methyl-5α-cholest-7-ene-4α-carbaldehyde + 2 ferrocytochrome b5 + O2 + 2 H+ = 3β-hydroxy-4β-methyl-5α-cholest-7-ene-4α-carboxylate + 2 ferricytochrome b5 + H2O

For diagram of reaction click here

Other name(s): methylsterol hydroxylase; 4-methylsterol oxidase; 4,4-dimethyl-5α-cholest-7-en-3β-ol,hydrogen-donor:oxygen oxidoreductase (hydroxylating)

Systematic name: 4,4-dimethyl-5α-cholest-7-en-3β-ol,ferrocytochrome-b5:oxygen oxidoreductase (hydroxylating)

Comments: Also acts on 4α-methyl-5α-cholest-7-en-3β-ol. The sterol can be based on cycloartenol as well as lanosterol.

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

References:

1. Miller, W.L., Kalafer, M.E., Gaylor, J.L. and Delwicke, C.V. Investigation of the component reactions of oxidative sterol demethylation. Study of the aerobic and anaerobic processes. Biochemistry 6 (1967) 2673-2678. [PMID: 4383278]

2. Gaylor, J.L. and Mason, H.S. Investigation of the component reactions of oxidative sterol demethylation. Evidence against participation of cytochrome P-450. J. Biol. Chem. 243 (1968) 4966-4972. [PMID: 4234469]

3. Brady, D.R., Crowder, R.D. and Hayes, W.J. Mixed function oxidases in sterol metabolism. Source of reducing equivalents. J. Biol. Chem. 255 (1980) 10624-10629. [PMID: 7430141]

4. Fukushima, H., Grinstead, G.F. and Gaylor, J.L. Total enzymic synthesis of cholesterol from lanosterol. Cytochrome b5-dependence of 4-methyl sterol oxidase. J. Biol. Chem. 256 (1981) 4822-4826. [PMID: 7228857]

5. Kawata, S., Trzaskos, J.M. and Gaylor, J.L. Affinity chromatography of microsomal enzymes on immobilized detergent-solubilized cytochrome b5. J. Biol. Chem. 261 (1986) 3790-3799. [PMID: 3949790]

6. Pascal, S., Taton, M. and Rahier, A. Plant sterol biosynthesis. Identification and characterization of two distinct microsomal oxidative enzymatic systems involved in sterol C4-demethylation. J. Biol. Chem. 268 (1993) 11639-11654. [PMID: 8505296]

7. Rahier, A., Smith, M. and Taton, M. The role of cytochrome b5 in 4α-methyl-oxidation and C5(6) desaturation of plant sterol precursors. Biochem. Biophys. Res. Commun. 236 (1997) 434-437. [PMID: 9240456]

[EC 1.14.18.9 created 1972 as EC 1.14.99.16, transferred 2002 to EC 1.14.13.72, transferred 2017 to EC 1.14.18.9]


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