EC - 3β-hydroxysteroid-4β-carboxylate 3-dehydrogenase (decarboxylating)

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IntEnz Enzyme Nomenclature


Accepted name:
3β-hydroxysteroid-4β-carboxylate 3-dehydrogenase (decarboxylating)
Other name:
sdmB (gene name)
Systematic name:
3β-hydroxysteroid-4β-carboxylate:NAD(P)+ 3-oxidoreductase (decarboxylating)



This bacterial enzyme participates in the biosynthesis of bacterial sterols. Together with EC, 4β-methylsterol monooxygenase (SdmA) 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-4β methyl group, turning it into a carboxylate group; SdmB is a bifunctional enzyme that catalyses two different activities. As EC it catalyses an oxidative decarboxylation that results in reduction of the 3β-hydroxy group at the C-3 carbon to an oxo group. As EC, 3β-hydroxysteroid 3-dehydrogenase, it reduces the 3-oxo group back to a 3β-hydroxyl. Since the remaining methyl group at C-4 is in an α orientation, it cannot serve as a substrate for a second round of demethylation by this system.

Links to other databases

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


  1. Lee, A. K., Banta, A. B., Wei, J. H., Kiemle, D. J., Feng, J., Giner, J. L., Welander, P. V.
    C-4 sterol demethylation enzymes distinguish bacterial and eukaryotic sterol synthesis.
    Proc. Natl. Acad. Sci. U.S.A. 115 : 5884-5889 (2018). [PMID: 29784781]

[EC created 2019]