KEGG   ENZYME: 1.14.18.10
Entry
EC 1.14.18.10               Enzyme                                 

Name
plant 4,4-dimethylsterol C-4alpha-methyl-monooxygenase;
SMO1 (gene name)
Class
Oxidoreductases;
Acting on paired donors, with incorporation or reduction of molecular oxygen;
With another compound as one donor, and incorporation of one atom of oxygen into the other donor
Sysname
24-methylidenecycloartanol,ferrocytochrome-b5:oxygen oxidoreductase (C-4alpha-methyl-hydroxylating)
Reaction(IUBMB)
24-methylidenecycloartanol + 6 ferrocytochrome b5 + 3 O2 + 6 H+ = 3beta-hydroxy-4beta,14alpha-dimethyl-9beta,19-cyclo-5alpha-ergost-24(241)-en-4alpha-carboxylate + 6 ferricytochrome b5 + 4 H2O (overall reaction) [RN:R12377];
(1a) 24-methylidenecycloartanol + 2 ferrocytochrome b5 + O2 + 2 H+ = 4alpha-(hydroxymethyl)-4beta,14alpha-dimethyl-9beta,19-cyclo-5alpha-ergost-24(241)-en-3beta-ol + 2 ferricytochrome b5 + H2O [RN:R12368];
(1b) 4alpha-(hydroxymethyl)-4beta,14alpha-dimethyl-9beta,19-cyclo-5alpha-ergost-24(241)-en-3beta-ol + 2 ferrocytochrome b5 + O2 + 2 H+ = 4alpha-formyl-4beta,14alpha-dimethyl-9beta,19-cyclo-5alpha-ergost-24(241)-en-3beta-ol + 2 ferricytochrome b5 + 2 H2O [RN:R12369];
(1c) 4alpha-formyl-4beta,14alpha-dimethyl-9beta,19-cyclo-5alpha-ergost-24(241)-en-3beta-ol + 2 ferrocytochrome b5 + O2 + 2 H+ = 3beta-hydroxy-4beta,14alpha-dimethyl-9beta,19-cyclo-5alpha-ergost-24(241)-en-4alpha-carboxylate + 2 ferricytochrome b5 + H2O [RN:R12370]
Reaction(KEGG)
Substrate
24-methylidenecycloartanol [CPD:C08830];
ferrocytochrome b5 [CPD:C00999];
O2 [CPD:C00007];
H+ [CPD:C00080];
4alpha-(hydroxymethyl)-4beta,14alpha-dimethyl-9beta,19-cyclo-5alpha-ergost-24(241)-en-3beta-ol;
4alpha-formyl-4beta,14alpha-dimethyl-9beta,19-cyclo-5alpha-ergost-24(241)-en-3beta-ol
Product
3beta-hydroxy-4beta,14alpha-dimethyl-9beta,19-cyclo-5alpha-ergost-24(241)-en-4alpha-carboxylate;
ferricytochrome b5 [CPD:C00996];
H2O [CPD:C00001];
4alpha-(hydroxymethyl)-4beta,14alpha-dimethyl-9beta,19-cyclo-5alpha-ergost-24(241)-en-3beta-ol;
4alpha-formyl-4beta,14alpha-dimethyl-9beta,19-cyclo-5alpha-ergost-24(241)-en-3beta-ol
Comment
This plant enzyme catalyses a step in the biosynthesis of sterols. It acts on the 4alpha-methyl group of the 4,4-dimethylated intermediate 24-methylidenecycloartanol and catalyses three successive oxidations, turning it into a carboxyl group. The carboxylate is subsequently removed by EC 1.1.1.418, plant 3beta-hydroxysteroid-4alpha-carboxylate 3-dehydrogenase (decarboxylating), which also catalyses the epimerization of the remaining 4beta-methyl into the 4alpha position. Unlike the fungal/animal enzyme EC 1.14.18.9, 4alpha-methylsterol monooxygenase, this enzyme is not able to remove the methyl group from C-4-monomethylated substrates. That activity is performed in plants by a second enzyme, EC 1.14.18.11, plant 4alpha-monomethylsterol monooxygenase.
History
EC 1.14.18.10 created 2019
Pathway
ec00100  Steroid biosynthesis
ec01100  Metabolic pathways
ec01110  Biosynthesis of secondary metabolites
Orthology
K14423  plant 4,4-dimethylsterol C-4alpha-methyl-monooxygenase
Genes
ATH: AT4G12110(SMO1-1) AT4G22755 AT4G22756(SMO1-2)
ALY: 110226378 110226382 9310821
CRB: 111829641 111829642 17878277 17884650
CSAT: 104707512 104717801 104718035 104718036 104720179 104722765 104722766 104722767 104731224 104731225 104733374 104737226
EUS: EUTSA_v10024722mg EUTSA_v10025849mg EUTSA_v10028846mg
BRP: 103853483 103860261 103860313
BNA: 106375731 106375734 106376549 106376550 106395025 106440893 106440900
BOE: 106323132 106323529 106326927
RSZ: 108819044 108822182 108826950
THJ: 104813000 104813925
LJA: Lj4g3v1302690.1(Lj4g3v1302690.1)
CSV: 101211692
CMO: 103490939
MCHA: 111020420
QSU: 111999469
VVI: 100255536
LSV: 111918756
DOSA: Os03t0108500-01(Os03g0108500) Os10t0545200-01(Os10g0545200)
OBR: 102723086
ATS: 109735447(LOC109735447) 109742913(LOC109742913) 109743100(LOC109743100) 109752552(LOC109752552) 109759404(LOC109759404)
DCT: 110101909
PEQ: 110036326
ATR: 18441549
 » show all
Reference
1  [PMID:8505296]
  Authors
Pascal S, Taton M, Rahier A
  Title
Plant sterol biosynthesis. Identification and characterization of two distinct microsomal oxidative enzymatic systems involved in sterol C4-demethylation.
  Journal
J Biol Chem 268:11639-54 (1993)
Reference
2  [PMID:9240456]
  Authors
Rahier A, Smith M, Taton M.
  Title
The role of cytochrome b5 in 4alpha-methyl-oxidation and C5(6) desaturation of plant sterol precursors.
  Journal
Biochem Biophys Res Commun 236:434-7 (1997)
DOI:10.1006/bbrc.1997.6974
Reference
3  [PMID:11707264]
  Authors
Darnet S, Bard M, Rahier A
  Title
Functional identification of sterol-4alpha-methyl oxidase cDNAs from Arabidopsis thaliana by complementation of a yeast erg25 mutant lacking sterol-4alpha-methyl oxidation.
  Journal
FEBS Lett 508:39-43 (2001)
DOI:10.1016/S0014-5793(01)03002-2
Reference
4  [PMID:14653780]
  Authors
Darnet S, Rahier A
  Title
Plant sterol biosynthesis: identification of two distinct families of sterol 4alpha-methyl oxidases.
  Journal
Biochem J 378:889-98 (2004)
DOI:10.1042/BJ20031572
  Sequence
Other DBs
ExplorEnz - The Enzyme Database: 1.14.18.10
IUBMB Enzyme Nomenclature: 1.14.18.10
ExPASy - ENZYME nomenclature database: 1.14.18.10
BRENDA, the Enzyme Database: 1.14.18.10

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