ID   1.1.1.417
DE   3beta-hydroxysteroid-4beta-carboxylate 3-dehydrogenase (decarboxylating).
CA   (1) a 3beta-hydroxy-4alpha-methylsteroid-4beta-carboxylate + NAD(+) =
CA   a 4alpha-methyl-3-oxosteroid + CO2 + NADH.
CA   (2) a 3beta-hydroxy-4alpha-methylsteroid-4beta-carboxylate + NADP(+) =
CA   a 4alpha-methyl-3-oxosteroid + CO2 + NADPH.
CC   -!- This bacterial enzyme participates in the biosynthesis of bacterial
CC       sterols.
CC   -!- Together with EC 1.14.13.246 (SdmA) it forms an enzyme system that
CC       removes one methyl group from the C-4 position of 4,4-dimethylated
CC       steroid molecules.
CC   -!- SdmA catalyzes three successive oxidations of the C-4beta methyl
CC       group, turning it into a carboxylate group; SdmB is a bifunctional
CC       enzyme that catalyzes two different activities.
CC   -!- As EC 1.1.1.417 it catalyzes an oxidative decarboxylation that
CC       results in reduction of the 3beta-hydroxy group at the C-3 carbon to
CC       an oxo group.
CC   -!- As EC 1.1.1.270, it reduces the 3-oxo group back to a 3beta-hydroxyl.
CC   -!- Since the remaining methyl group at C-4 is in an alpha orientation,
CC       it cannot serve as a substrate for a second round of demethylation by
CC       this system.
DR   Q60A54, SDMB_METCA ;
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