The Enzyme Database

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Accepted name: 3β-hydroxysteroid-4α-carboxylate 3-dehydrogenase (decarboxylating)
Reaction: a 3β-hydroxysteroid-4α-carboxylate + NAD(P)+ = a 3-oxosteroid + CO2 + NAD(P)H
For diagram of sterol ring A modification, click here
Other name(s): 3β-hydroxy-4β-methylcholestenecarboxylate 3-dehydrogenase (decarboxylating); 3β-hydroxy-4β-methylcholestenoate dehydrogenase; sterol 4α-carboxylic decarboxylase; sterol-4α-carboxylate 3-dehydrogenase (decarboxylating) (ambiguous); ERG26 (gene name); NSDHL (gene name)
Systematic name: 3β-hydroxysteroid-4α-carboxylate:NAD(P)+ 3-oxidoreductase (decarboxylating)
Comments: 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, 4α-methylsterol monooxygenase, catalyses three successive oxidations of the methyl group, resulting in a carboxyl group; the second enzyme, EC, catalyses an oxidative decarboxylation that results in a reduction of the 3β-hydroxy group at the C-3 carbon to an oxo group; and the last enzyme, EC, 3β-hydroxysteroid 3-dehydrogenase, reduces the 3-oxo group back to a 3β-hydroxyl. If a second methyl group remains at the C-4 position, this enzyme also catalyses its epimerization from 4β to 4α orientation, so it could serve as a substrate for a second round of demethylation. cf. EC, plant 3β-hydroxysteroid-4α-carboxylate 3-dehydrogenase (decarboxylating).
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 71822-23-6
1.  Sharpless, K.B., Snyder, T.E., Spencer, T.A., Maheshwari, K.K. and Nelson, J.A. Biological demethylation of 4,4-dimethyl sterols, Evidence for enzymic epimerization of the 4β-methyl group prior to its oxidative removal. J. Am. Chem. Soc. 91 (1969) 3394–3396. [PMID: 5791927]
2.  Rahimtula, A.D. and Gaylor, J.L. Partial purification of a microsomal sterol 4α-carboxylic acid decarboxylase. J. Biol. Chem. 247 (1972) 9–15. [PMID: 4401584]
3.  Brady, D.R., Crowder, R.D. and Hayes, W.J. Mixed function oxidases in sterol metabolism. Source of reducing equivalents. J. Biol. Chem. 255 (1980) 10624–10629. [PMID: 7430141]
4.  Gachotte, D., Barbuch, R., Gaylor, J., Nickel, E. and Bard, M. Characterization of the Saccharomyces cerevisiae ERG26 gene encoding the C-3 sterol dehydrogenase (C-4 decarboxylase) involved in sterol biosynthesis. Proc. Natl. Acad. Sci. USA 95 (1998) 13794–13799. [DOI] [PMID: 9811880]
5.  Caldas, H. and Herman, G.E. NSDHL, an enzyme involved in cholesterol biosynthesis, traffics through the Golgi and accumulates on ER membranes and on the surface of lipid droplets. Hum. Mol. Genet. 12 (2003) 2981–2991. [DOI] [PMID: 14506130]
[EC created 1978, modified 2002, modified 2012, modified 2019]

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