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

BRENDA

EC2PDB

ExplorEnz

PRIAM enzyme-specific profiles

KEGG Ligand Database for Enzyme Nomenclature

IUBMB Enzyme Nomenclature

IntEnz

MEDLINE

MetaCyc

Rhea expert-curated reactions

UniProtKB/Swiss-Prot

All UniProtKB/Swiss-Prot entries referenced in this entry, with possibility to download in different formats, align etc.

All ENZYME / UniProtKB/Swiss-Prot entries corresponding to 1.1.1.-
All ENZYME / UniProtKB/Swiss-Prot entries corresponding to 1.1.-.-
All ENZYME / UniProtKB/Swiss-Prot entries corresponding to 1.-.-.-