EC              Enzyme                                 

4beta-methylsterol monooxygenase;
sdmA (gene name)
Acting on paired donors, with incorporation or reduction of molecular oxygen;
With NADH or NADPH as one donor, and incorporation of one atom of oxygen into the other donor
3beta-hydroxy-4,4-dimethylsteroid,NADH:oxygen oxidoreductase (C-4mbeta-hydroxylating)
a 3beta-hydroxy-4,4-dimethylsteroid + 3 NADH + 3 H+ + 3 O2 = a 3beta-hydroxy-4alpha-methylsteroid-4beta-carboxylate + 3 NAD+ + 4 H2O (overall reaction) [RN:R12360];
(1a) a 3beta-hydroxy-4,4-dimethylsteroid + NADH + H+ + O2 = a 3beta-hydroxy-4beta-hydroxymethyl-4alpha-methylsteroid + NAD+ + H2O [RN:R12357];
(1b) a 3beta-hydroxy-4beta-hydroxymethyl-4alpha-methylsteroid + NADH + H+ + O2 = a 3beta-hydroxy-4beta-formyl-4alpha-methylsteroid + NAD+ + 2 H2O [RN:R12358];
(1c) a 3beta-hydroxy-4beta-formyl-4alpha-methylsteroid + NADH + H+ + O2 = a 3beta-hydroxy-4alpha-methylsteroid-4beta-carboxylate + NAD+ + H2O [RN:R12359]
3beta-hydroxy-4,4-dimethylsteroid [CPD:C22103];
NADH [CPD:C00004];
H+ [CPD:C00080];
O2 [CPD:C00007];
3beta-hydroxy-4beta-hydroxymethyl-4alpha-methylsteroid [CPD:C22104];
3beta-hydroxy-4beta-formyl-4alpha-methylsteroid [CPD:C22105]
3beta-hydroxy-4alpha-methylsteroid-4beta-carboxylate [CPD:C22106];
NAD+ [CPD:C00003];
H2O [CPD:C00001];
3beta-hydroxy-4beta-hydroxymethyl-4alpha-methylsteroid [CPD:C22104];
3beta-hydroxy-4beta-formyl-4alpha-methylsteroid [CPD:C22105]
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-4beta methyl group, turning it into a carboxylate group; the second enzyme, SdmB, is a bifunctional enzyme that catalyses two different activities. As EC, 3beta-hydroxysteroid-4beta-carboxylate 3-dehydrogenase (decarboxylating), it catalyses an oxidative decarboxylation that results in reduction of the 3beta-hydroxy group at the C-3 carbon to an oxo group. As EC, 3beta-hydroxysteroid 3-dehydrogenase, it reduces the 3-oxo group back to a 3beta-hydroxyl. Unlike the animal/fungal enzyme EC, 4alpha-methylsterol monooxygenase, and the plant enzymes EC, plant 4,4-dimethylsterol C-4alpha-methyl-monooxygenase, and EC, plant 4alpha-monomethylsterol monooxygenase, this enzyme acts preferentially on the 4beta-methyl group. Since no epimerization of the remaining C-4alpha methyl group occurs, the enzyme can only remove one methyl group, leaving a 4alpha-monomethylated product. Known substrates include 4,4-dimethyl-5alpha-cholest-8-en-3beta-ol and 14-demethyllanosterol.
EC created 2019
K23556  4beta-methylsterol monooxygenase
MCA: MCA1016
METU: GNH96_12925
MMAI: sS8_3007
MMOB: F6R98_01405
MISZ: MishRS11D_00090
SAMY: DB32_006293
MRM: A7982_00877
1  [PMID:29784781]
Lee AK, Banta AB, Wei JH, Kiemle DJ, Feng J, Giner JL, Welander PV
C-4 sterol demethylation enzymes distinguish bacterial and eukaryotic sterol synthesis.
Proc Natl Acad Sci U S A 115:5884-5889 (2018)
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