Reaction: S-adenosyl-L-methionine + 5α-cholesta-8,24-dien-3β-ol = S-adenosyl-L-homocysteine + 24-methylene-5α-cholest-8-en-3β-ol
For diagram click here.
desmosterol = cholesta-5,24-dien-3β-ol
zymostrol = 5α-cholesta-8,24-dien-3β-ol
Other name(s): δ24-methyltransferase; δ24-sterol methyltransferase; zymosterol-24-methyltransferase; S-adenosyl-4-methionine:sterol δ24-methyltransferase; SMT1; 24-sterol C-methyltransferase; S-adenosyl-L-methionine:δ24(23)-sterol methyltransferase; phytosterol methyltransferase
Systematic name: S-adenosyl-L-methionine:zymosterol 24-C-methyltransferase
Comments: Requires glutathione. Acts on a range of sterols with a 24(25)-double bond in the sidechain. While zymosterol is the preferred substrate it also acts on desmosterol, 5α-cholesta-7,24-dien-3β-ol, 5α-cholesta-5,7,24-trien-3β-ol, 4α-methylzymosterol and others. S-Adenosyl-L-methionine attacks the Si-face of the 24(25) double bond and the C-24 hydrogen is transferred to C-25 on the Re face of the double bond.
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number: 37257-07-1
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