ID   1.1.1.170
DE   3beta-hydroxysteroid-4alpha-carboxylate 3-dehydrogenase
DE   (decarboxylating).
AN   3beta-hydroxy-4alpha-methylcholestenecarboxylate 3-dehydrogenase
AN   (decarboxylating).
AN   3beta-hydroxy-4beta-methylcholestenecarboxylate 3-dehydrogenase
AN   (decarboxylating).
AN   3beta-hydroxy-4beta-methylcholestenoate dehydrogenase.
AN   sterol-4alpha-carboxylate 3-dehydrogenase (decarboxylating).
AN   sterol 4alpha-carboxylic decarboxylase.
CA   (1) a 3beta-hydroxysteroid-4alpha-carboxylate + NADP(+) = a 3-oxosteroid
CA   + CO2 + NADPH.
CA   (2) a 3beta-hydroxysteroid-4alpha-carboxylate + NAD(+) = a 3-oxosteroid +
CA   CO2 + NADH.
CC   -!- The enzyme participates in the biosynthesis of several important
CC       sterols such as ergosterol and cholesterol.
CC   -!- It is part of a three enzyme system that removes methyl groups from
CC       the C-4 position of steroid molecules.
CC   -!- The first enzyme, EC 1.14.18.9, catalyzes three successive oxidations
CC       of the methyl group, resulting in a carboxyl group; the second
CC       enzyme, EC 1.1.1.170, catalyzes an oxidative decarboxylation that
CC       results in a reduction of the 3beta-hydroxy group at the C-3 carbon
CC       to an oxo group; and the last enzyme, EC 1.1.1.270, reduces the 3-oxo
CC       group back to a 3beta-hydroxyl.
CC   -!- If a second methyl group remains at the C-4 position, this enzyme
CC       also catalyzes its epimerization from 4beta to 4alpha orientation,
CC       so it could serve as a substrate for a second round of demethylation.
CC       cf. EC 1.1.1.418.
DR   Q5A1B0, ERG26_CANAL;  O43050, ERG26_SCHPO;  P53199, ERG26_YEAST;
DR   A9X4U2, HSDD3_ARATH;  Q3ZBE9, NSDHL_BOVIN;  Q54L85, NSDHL_DICDI;
DR   Q15738, NSDHL_HUMAN;  Q9R1J0, NSDHL_MOUSE;  Q5PPL3, NSDHL_RAT  ;
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