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, 4¦Á-methylsterol monooxygenase, catalyses three successive oxidations of the methyl group, resulting in a carboxyl group; the second enzyme, EC 1.1.1.170, catalyses an oxidative decarboxylation that results in a reduction of the 3¦Â-hydroxy group at the C-3 carbon to an oxo group; and the last enzyme, EC 1.1.1.270, 3¦Â-hydroxysteroid 3-dehydrogenase, reduces the 3-oxo group back to a 3¦Â-hydroxyl. If a second methyl group remains at the C-4 position, this enzyme also catalyses its epimerization from 4¦Â to 4¦Á orientation, so it could serve as a substrate for a second round of demethylation. cf. EC 1.1.1.418, plant 3¦Â-hydroxysteroid-4¦Á-carboxylate 3-dehydrogenase (decarboxylating).
Cofactor
History
Reactions
A 3-beta-hydroxysteroid-4-alpha-carboxylate + NAD(P)(+) = a 3-oxosteroid + CO(2) + NAD(P)H.
