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Information on EC - 3beta-hydroxysteroid-4alpha-carboxylate 3-dehydrogenase (decarboxylating)

for references in articles please use BRENDA:EC1.1.1.170
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IUBMB 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, 4alpha-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 3beta-hydroxy group at the C-3 carbon to an oxo group; and the last enzyme, EC, 3beta-hydroxysteroid 3-dehydrogenase, reduces the 3-oxo group back to a 3beta-hydroxyl. If a second methyl group remains at the C-4 position, this enzyme also catalyses its epimerization from 4beta to 4alpha orientation, so it could serve as a substrate for a second round of demethylation. cf. EC, plant 3beta-hydroxysteroid-4alpha-carboxylate 3-dehydrogenase (decarboxylating).
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The expected taxonomic range for this enzyme is: Bacteria, Eukaryota
nsdhl, erg26, erg26p, sterol-4-alpha-carboxylate 3-dehydrogenase, sterol-4-alpha-carboxylate-3-dehydrogenase, sterol-4alpha-carboxylate 3-dehydrogenase, more
3beta-hydroxy-4beta-methyl-5alpha-cholest-7-ene-4alpha-carboxylate + NAD(P)+ = 4alpha-methyl-5alpha-cholest-7-en-3-one + CO2 + NAD(P)H + H+
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