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Information on EC 1.14.13.246 - 4beta-methylsterol monooxygenase

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IUBMB Comments
Contains a Rieske [2Fe-2S] iron-sulfur cluster. This bacterial enzyme (SdmA) participates in the biosynthesis of bacterial sterols. Together with SdmB it forms an enzyme system that removes one methyl group from the C-4 position of 4,4-dimethylated steroid molecules. SdmA catalyses three successive oxidations of the C-4beta methyl group, turning it into a carboxylate group; the second enzyme, SdmB, is a bifunctional enzyme that catalyses two different activities. As EC 1.1.1.417, 3beta-hydroxysteroid-4beta-carboxylate 3-dehydrogenase (decarboxylating), it catalyses an oxidative decarboxylation that results in reduction of the 3beta-hydroxy group at the C-3 carbon to an oxo group. As EC 1.1.1.270, 3beta-hydroxysteroid 3-dehydrogenase, it reduces the 3-oxo group back to a 3beta-hydroxyl. Unlike the animal/fungal enzyme EC 1.14.18.9, 4alpha-methylsterol monooxygenase, and the plant enzymes EC 1.14.18.10, plant 4,4-dimethylsterol C-4alpha-methyl-monooxygenase, and EC 1.14.18.11, plant 4alpha-monomethylsterol monooxygenase, this enzyme acts preferentially on the 4beta-methyl group. Since no epimerization of the remaining C-4alpha methyl group occurs, the enzyme can only remove one methyl group, leaving a 4alpha-monomethylated product. Known substrates include 4,4-dimethyl-5alpha-cholest-8-en-3beta-ol and 14-demethyllanosterol.
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The expected taxonomic range for this enzyme is: Methylococcus capsulatus
Reaction Schemes
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Synonyms
SdmA, more
REACTION
REACTION DIAGRAM
COMMENTARY hide
ORGANISM
UNIPROT
LITERATURE
a 3beta-hydroxy-4,4-dimethylsteroid + 3 NADH + 3 H+ + 3 O2 = a 3beta-hydroxy-4alpha-methylsteroid-4beta-carboxylate + 3 NAD+ + 4 H2O
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overall reaction
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a 3beta-hydroxy-4,4-dimethylsteroid + NADH + H+ + O2 = a 3beta-hydroxy-4beta-hydroxymethyl-4alpha-methylsteroid + NAD+ + H2O
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(1a)
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a 3beta-hydroxy-4beta-formyl-4alpha-methylsteroid + NADH + H+ + O2 = a 3beta-hydroxy-4alpha-methylsteroid-4beta-carboxylate + NAD+ + H2O
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(1c)
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a 3beta-hydroxy-4beta-hydroxymethyl-4alpha-methylsteroid + NADH + H+ + O2 = a 3beta-hydroxy-4beta-formyl-4alpha-methylsteroid + NAD+ + 2 H2O
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(1b)
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