EC Explorer

1.14.18.10

plant 4,4-dimethylsterol C-4α-methyl-monooxygenase

24-methylidenecycloartanol + 6 ferrocytochrome b₅ + 3 O₂ + 6 H⁺ = 3β-hydroxy-4β,14α-dimethyl-9β,19-cyclo-5α-ergost-24(24¹)-en-4α-carboxylate + 6 ferricytochrome b₅ + 4 H₂O (overall reaction);;(1a) 24-methylidenecycloartanol + 2 ferrocytochrome b₅ + O₂ + 2 H⁺ = 4α-(hydroxymethyl)-4β,14α-dimethyl-9β,19-cyclo-5α-ergost-24(24¹)-en-3β-ol + 2 ferricytochrome b₅ + H₂O;;(1b) 4α-(hydroxymethyl)-4β,14α-dimethyl-9β,19-cyclo-5α-ergost-24(24¹)-en-3β-ol + 2 ferrocytochrome b₅ + O₂ + 2 H⁺ = 4α-formyl-4β,14α-dimethyl-9β,19-cyclo-5α-ergost-24(24¹)-en-3β-ol + 2 ferricytochrome b₅ + 2 H₂O;;(1c) 4α-formyl-4β,14α-dimethyl-9β,19-cyclo-5α-ergost-24(24¹)-en-3β-ol + 2 ferrocytochrome b₅ + O₂ + 2 H⁺ = 3β-hydroxy-4β,14α-dimethyl-9β,19-cyclo-5α-ergost-24(24¹)-en-4α-carboxylate + 2 ferricytochrome b₅ + H₂O

SMO1 (gene name)

24-methylidenecycloartanol,ferrocytochrome-b₅:oxygen oxidoreductase (C-4α-methyl-hydroxylating)

This plant enzyme catalyses a step in the biosynthesis of sterols. It acts on the 4α-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 3β-hydroxysteroid-4α-carboxylate 3-dehydrogenase (decarboxylating), which also catalyses the epimerization of the remaining 4β-methyl into the 4α position. Unlike the fungal/animal enzyme EC 1.14.18.9, 4α-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 4α-monomethylsterol monooxygenase.

created 2019