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Information on EC 1.14.18.11 - plant 4alpha-monomethylsterol monooxygenase and Organism(s) Arabidopsis thaliana and UniProt Accession Q9ZW22
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1.14.18.11 plant 4alpha-monomethylsterol monooxygenaseIUBMB Comments
This plant enzyme catalyses a step in the biosynthesis of sterols. It acts on the methyl group of the 4alpha-methylated intermediates 24-ethylidenelophenol and 24-methylidenelophenol and catalyses three successive oxidations, turning it into a carboxyl group. The carboxylate is subsequently removed by EC 1.1.1.418, plant 3beta-hydroxysteroid-4alpha-carboxylate 3-dehydrogenase (decarboxylating). Unlike the fungal/animal enzyme EC 1.14.18.9, 4alpha-methylsterol monooxygenase, this enzyme is not able to act on 4,4-dimethylated substrates. That activity, which occurs earlier in the pathway, is performed in plants by a second enzyme, EC 1.14.18.10, plant 4,4-dimethylsterol C-4alpha-methyl-monooxygenase.
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The taxonomic range for the selected organisms is: Arabidopsis thaliana
The enzyme appears in selected viruses and cellular organisms
The enzyme appears in selected viruses and cellular organisms
Reaction Schemes
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Synonyms
smo2-1, smo2-2, 4alpha-mso, sterol-4alpha-methyl oxidase 2, 
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topSYNONYM 
ORGANISM
UNIPROT
COMMENTARY 
LITERATURE
SMO2
SMO2
-
-
-
-
SYSTEMATIC NAME
IUBMB Comments
24-ethylidenelophenol,ferrocytochrome-b5:oxygen oxidoreductase (C-4alpha-methyl-hydroxylating)
This plant enzyme catalyses a step in the biosynthesis of sterols. It acts on the methyl group of the 4alpha-methylated intermediates 24-ethylidenelophenol and 24-methylidenelophenol and catalyses three successive oxidations, turning it into a carboxyl group. The carboxylate is subsequently removed by EC 1.1.1.418, plant 3beta-hydroxysteroid-4alpha-carboxylate 3-dehydrogenase (decarboxylating). Unlike the fungal/animal enzyme EC 1.14.18.9, 4alpha-methylsterol monooxygenase, this enzyme is not able to act on 4,4-dimethylated substrates. That activity, which occurs earlier in the pathway, is performed in plants by a second enzyme, EC 1.14.18.10, plant 4,4-dimethylsterol C-4alpha-methyl-monooxygenase.
SUBSTRATE
PRODUCT
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate)
(Substrate)
LITERATURE
(Substrate)
(Substrate)
COMMENTARY
(Product)
(Product)
LITERATURE
(Product)
(Product)
Reversibility
r=reversible
ir=irreversible
?=not specified
r=reversible
ir=irreversible
?=not specified
3beta-hydroxy-4beta-methyl-5alpha-cholest-7-ene-4alpha-carbaldehyde + a ferrocytochrome + O2
3beta-hydroxy-4beta-methyl-5alpha-cholest-7-ene-4alpha-carboxylate + a ferricytochrome + H2O
step 3 of 3 of the overall reaction
-
-
?
4,4-dimethyl-5alpha-cholest-7-en-3beta-ol + a ferrocytochrome + O2
4beta-hydroxymethyl-4alpha-methyl-5alpha-cholest-7-en-3beta-ol + a ferricytochrome + H2O
step 1 of 3 of the overall reaction
-
-
?
4beta-hydroxymethyl-4alpha-methyl-5alpha-cholest-7-en-3beta-ol + a ferrocytochrome + O2
3beta-hydroxy-4beta-methyl-5alpha-cholest-7-ene-4alpha-carbaldehyde + a ferricytochrome + H2O
step 2 of 3 of the overall reaction
-
-
?
(3alpha,4alpha,5alpha,10alpha,13alpha,20S)-4-methyl-9,19-cycloergosta-7,24(28)-dien-3-ol + 6 ferrocytochrome b5 + 3 O2 + 6 H+
(3alpha,4alpha,5alpha,10alpha,13alpha,20S)-3-hydroxy-9,19-cycloergosta-7,24(28)-diene-4-carboxylic acid + 6 ferricytochrome b5 + 4 H2O
-
-
-
-
ir
(3alpha,4alpha,5alpha,10alpha,13alpha,20S)-4-methylcholest-7-en-3-ol + 6 ferrocytochrome b5 + 3 O2 + 6 H+
(3alpha,4alpha,5alpha,10alpha,13alpha,20S)-3-hydroxycholest-7-ene-4-carboxylic acid + 6 ferricytochrome b5 + 4 H2O
-
-
-
-
ir
24-ethylidenelophenol + 6 ferrocytochrome b5 + 3 O2 + 6 H+
3beta,4alpha,5alpha-3-hydroxystigmasta-7,24(28)-diene-4-carboxylate + 6 ferricytochrome b5 + 4 H2O
-
-
-
-
?
24-methylidenelophenol + 6 ferrocytochrome b5 + 3 O2 + 6 H+
3beta-hydroxyergosta-7,24(241)-dien-4alpha-carboxylate + 6 ferricytochrome b5 + 4 H2O
-
-
-
-
ir
3beta-hydroxy-4beta-methyl-5alpha-cholest-7-ene-4alpha-carbaldehyde + a ferrocytochrome + O2
3beta-hydroxy-4beta-methyl-5alpha-cholest-7-ene-4alpha-carboxylate + a ferricytochrome + H2O
step 3 of 3 of the overall reaction
-
-
?
4,4-dimethyl-5alpha-cholest-7-en-3beta-ol + a ferrocytochrome + O2
4beta-hydroxymethyl-4alpha-methyl-5alpha-cholest-7-en-3beta-ol + a ferricytochrome + H2O
step 1 of 3 of the overall reaction
-
-
?
4beta-hydroxymethyl-4alpha-methyl-5alpha-cholest-7-en-3beta-ol + a ferrocytochrome + O2
3beta-hydroxy-4beta-methyl-5alpha-cholest-7-ene-4alpha-carbaldehyde + a ferricytochrome + H2O
step 2 of 3 of the overall reaction
-
-
?
additional information
?
-
conversion of cycloartenol into functional phytosterol requires the removal of 2 methyl groups at C4 by the enzymic complex including the sterol 4alpha-methyl oxidase SMO
-
-
?
additional information
?
-
conversion of cycloartenol into functional phytosterol requires the removal of 2 methyl groups at C4 by the enzymic complex including the sterol 4alpha-methyl oxidase SMO
-
-
?
additional information
?
-
conversion of cycloartenol into functional phytosterol requires the removal of 2 methyl groups at C4 by the enzymic complex including the sterol 4alpha-methyl oxidase SMO
-
-
?
additional information
?
-
conversion of cycloartenol into functional phytosterol requires the removal of 2 methyl groups at C4 by the enzymic complex including the sterol 4alpha-methyl oxidase SMO
-
-
?
NATURAL SUBSTRATE
NATURAL PRODUCT
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate)
(Substrate)
LITERATURE
(Substrate)
(Substrate)
COMMENTARY
(Product)
(Product)
LITERATURE
(Product)
(Product)
REVERSIBILITY
r=reversible
ir=irreversible
?=not specified
r=reversible
ir=irreversible
?=not specified
additional information
?
-
conversion of cycloartenol into functional phytosterol requires the removal of 2 methyl groups at C4 by the enzymic complex including the sterol 4alpha-methyl oxidase SMO
-
-
?
additional information
?
-
conversion of cycloartenol into functional phytosterol requires the removal of 2 methyl groups at C4 by the enzymic complex including the sterol 4alpha-methyl oxidase SMO
-
-
?
additional information
?
-
conversion of cycloartenol into functional phytosterol requires the removal of 2 methyl groups at C4 by the enzymic complex including the sterol 4alpha-methyl oxidase SMO
-
-
?
additional information
?
-
conversion of cycloartenol into functional phytosterol requires the removal of 2 methyl groups at C4 by the enzymic complex including the sterol 4alpha-methyl oxidase SMO
-
-
?
COFACTOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
METALS and IONS
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
INHIBITOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
ORGANISM
COMMENTARY
LITERATURE
UNIPROT
SEQUENCE DB
SOURCE
isozyme SMO2-1; 2 distinct enzyme families exist with 3 and 2 isozymes belonging to them, respectively
SwissProt
GENERAL INFORMATION
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
metabolism
enzyme expression in a yeast erg25 ergosterol auxotroph, lacking sterol-4alpha-methyl oxidase activity, restores growth and endogenous ergosterol synthesis
malfunction
-
when silencing the enzyme, an important accumulation of 4alpha-methyl-DELTA7-sterols is found, with no change in the levels of 4,4-dimethylsterols
metabolism
-
the enzyme is involved in the removal of the second C4-methyl group of phytosterol precursors
UNIPROT
ENTRY NAME
ORGANISM
NO. OF AA
NO. OF TRANSM. HELICES
MOLECULAR WEIGHT[Da]
SOURCE
SEQUENCE
LOCALIZATION PREDICTION
The reliability class of the localization prediction ranges from 1 (very reliable) to 5 (not reliable).
The reliability class of the localization prediction ranges from 1 (very reliable) to 5 (not reliable). SMO21_ARATH
272
4
31649
Swiss-Prot
other Location (Reliability: 5)
SUBUNIT
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
additional information
additional information
enzyme possesses 3 His-rich motifs common for membrane-bound non-heme iron oxygenases
additional information
enzyme possesses 3 His-rich motifs common for membrane-bound non-heme iron oxygenases
additional information
enzyme possesses 3 His-rich motifs common for membrane-bound non-heme iron oxygenases
additional information
enzyme possesses 3 His-rich motifs common for membrane-bound non-heme iron oxygenases
CLONED (Commentary)
ORGANISM
UNIPROT
LITERATURE
DNA and amino acid sequence determination and analysis, expression in enzyme-lacking Saccharomyces cerevisiae strain erg25
expressed in Saccharomyces cerevisiae erg25 ergosterol auxotroph strain
DNA and amino acid sequence determination and analysis, expression in enzyme-lacking Saccharomyces cerevisiae strain erg25
REF.
AUTHORS
TITLE
JOURNAL
VOL.
PAGES
YEAR
ORGANISM (UNIPROT)
PUBMED ID
SOURCE
Darnet, S.; Rahier, A.
Plant sterol biosynthesis: identification of two distinct families of sterol 4alpha-methyl oxidases
Biochem. J.
378
889-898
2004
Arabidopsis thaliana (Q8VWZ8), Arabidopsis thaliana (Q9ZW22), Nicotiana benthamiana (Q5J954), Nicotiana tabacum (Q6YAU6)
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
Arabidopsis thaliana (Q9ZW22)
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