EC - Plant 4,4-dimethylsterol C-4α-methyl-monooxygenase

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IntEnz Enzyme Nomenclature


Accepted name:
plant 4,4-dimethylsterol C-4α-methyl-monooxygenase
Other name:
SMO1 (gene name)
Systematic name:
24-methylenecycloartanol,ferrocytochrome-b5:oxygen oxidoreductase (C-4α-methyl-hydroxylating)



This plant enzyme catalyses a step in the biosynthesis of sterols. It acts on the 4α-methyl group of the 4,4-dimethylated intermediate 24-methylenecycloartanol and catalyses three successive oxidations, turning it into a carboxyl group. The carboxylate is subsequently removed by EC, plant 3β-hydroxysteroid-4α-carboxylate 3-dehydrogenase (decarboxylating), which also catalyses the epimerization of the remaining 4β-methyl into the 4α position. Unlike the fungal/animal enzyme EC, 4α-methylsterol monooxygenase, this enzyme is not able to remove the methyl group from C-4-monomethylated substrates. That activity is performed in plants by a second enzyme, EC, plant 4α-monomethylsterol monooxygenase.

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB


  1. Pascal, S., Taton, M., Rahier, A.
    Plant sterol biosynthesis. Identification and characterization of two distinct microsomal oxidative enzymatic systems involved in sterol C4-demethylation.
    J. Biol. Chem. 268 : 11639-11654 (1993). [PMID: 8505296]
  2. Rahier, A., Smith, M., Taton, M.
    The role of cytochrome b5 in 4alpha-methyl-oxidation and C5(6) desaturation of plant sterol precursors.
    Biochem. Biophys. Res. Commun. 236 : 434-437 (1997). [PMID: 9240456]
  3. Darnet, S., Bard, M., Rahier, A.
    Functional identification of sterol-4alpha-methyl oxidase cDNAs from Arabidopsis thaliana by complementation of a yeast erg25 mutant lacking sterol-4alpha-methyl oxidation.
    FEBS Lett. 508 : 39-43 (2001). [PMID: 11707264]
  4. Darnet, S., Rahier, A.
    Plant sterol biosynthesis: identification of two distinct families of sterol 4alpha-methyl oxidases.
    Biochem. J. 378 : 889-898 (2004). [PMID: 14653780]

[EC created 2019]