EC Explorer

1.14.13.246

4β-methylsterol monooxygenase

a 3β-hydroxy-4,4-dimethylsteroid + 3 NADH + 3 H⁺ + 3 O₂ = a 3β-hydroxy-4α-methylsteroid-4β-carboxylate + 3 NAD⁺ + 4 H₂O (overall reaction);;(1a) a 3β-hydroxy-4,4-dimethylsteroid + NADH + H⁺ + O₂ = a 3β-hydroxy-4β-hydroxymethyl-4α-methylsteroid + NAD⁺ + H₂O;;(1b) a 3β-hydroxy-4β-hydroxymethyl-4α-methylsteroid + NADH + H⁺ + O₂ = a 3β-hydroxy-4β-formyl-4α-methylsteroid + NAD⁺ + 2 H₂O;;(1c) a 3β-hydroxy-4β-formyl-4α-methylsteroid + NADH + H⁺ + O₂ = a 3β-hydroxy-4α-methylsteroid-4β-carboxylate + NAD⁺ + H₂O

sdmA (gene name)

3β-hydroxy-4,4-dimethylsteroid,NADH:oxygen oxidoreductase (C-4mβ-hydroxylating)

Contains a Rieske [2Fe-2S] iron-sulfur cluster. This bacterial enzyme (SdmA) participates in the biosynthesis of bacterial sterols. Together with SdmB it forms an enzyme system that removes one methyl group from the C-4 position of 4,4-dimethylated steroid molecules. SdmA catalyses three successive oxidations of the C-4β methyl group, turning it into a carboxylate group; the second enzyme, SdmB, is a bifunctional enzyme that catalyses two different activities. As EC 1.1.1.417, 3β-hydroxysteroid-4β-carboxylate 3-dehydrogenase (decarboxylating), it catalyses an oxidative decarboxylation that results in reduction of the 3β-hydroxy group at the C-3 carbon to an oxo group. As EC 1.1.1.270, 3β-hydroxysteroid 3-dehydrogenase, it reduces the 3-oxo group back to a 3β-hydroxyl. Unlike the animal/fungal enzyme EC 1.14.18.9, 4α-methylsterol monooxygenase, and the plant enzymes EC 1.14.18.10, plant 4,4-dimethylsterol C-4α-methyl-monooxygenase, and EC 1.14.18.11, plant 4α-monomethylsterol monooxygenase, this enzyme acts preferentially on the 4β-methyl group. Since no epimerization of the remaining C-4α methyl group occurs, the enzyme can only remove one methyl group, leaving a 4α-monomethylated product. Known substrates include 4,4-dimethyl-5α-cholest-8-en-3β-ol and 14-demethyllanosterol.

created 2019