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ENZYME entry: EC 1.1.1.170

Accepted Name
3beta-hydroxysteroid-4alpha-carboxylate 3-dehydrogenase (decarboxylating).
Alternative Name(s)
3beta-hydroxy-4alpha-methylcholestenecarboxylate 3-dehydrogenase (decarboxylating).
3beta-hydroxy-4beta-methylcholestenecarboxylate 3-dehydrogenase (decarboxylating).
3beta-hydroxy-4beta-methylcholestenoate dehydrogenase.
sterol-4alpha-carboxylate 3-dehydrogenase (decarboxylating).
sterol 4alpha-carboxylic decarboxylase.
Reaction catalysed
  • a 3beta-hydroxysteroid-4alpha-carboxylate + NADP(+) <=> a 3-oxosteroid + CO2 + NADPH
  • a 3beta-hydroxysteroid-4alpha-carboxylate + NAD(+) <=> a 3-oxosteroid + CO2 + NADH
Comment(s)
  • The enzyme participates in the biosynthesis of several important sterols such as ergosterol and cholesterol.
  • It is part of a three enzyme system that removes methyl groups from the C-4 position of steroid molecules.
  • The first enzyme, EC 1.14.18.9, catalyzes three successive oxidations of the methyl group, resulting in a carboxyl group; the second enzyme, EC 1.1.1.170, catalyzes an oxidative decarboxylation that results in a reduction of the 3beta-hydroxy group at the C-3 carbon to an oxo group; and the last enzyme, EC 1.1.1.270, reduces the 3-oxo group back to a 3beta-hydroxyl.
  • If a second methyl group remains at the C-4 position, this enzyme also catalyzes its epimerization from 4beta to 4alpha orientation, so it could serve as a substrate for a second round of demethylation.
  • Cf. EC 1.1.1.418.
Cross-references
BRENDA1.1.1.170
EC2PDB1.1.1.170
ExplorEnz1.1.1.170
PRIAM enzyme-specific profiles1.1.1.170
KEGG Ligand Database for Enzyme Nomenclature1.1.1.170
IUBMB Enzyme Nomenclature1.1.1.170
IntEnz1.1.1.170
MEDLINEFind literature relating to 1.1.1.170
MetaCyc1.1.1.170
Rhea expert-curated reactions1.1.1.170
UniProtKB/Swiss-Prot
Q5A1B0, ERG26_CANAL;  O43050, ERG26_SCHPO;  P53199, ERG26_YEAST;  
A9X4U2, HSDD3_ARATH;  Q3ZBE9, NSDHL_BOVIN;  Q54L85, NSDHL_DICDI;  
Q15738, NSDHL_HUMAN;  Q9R1J0, NSDHL_MOUSE;  Q5PPL3, NSDHL_RAT;  

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