Squalene methyltransferase

Squalene methyltransferase (EC 2.1.1.262, TMT-1, TMT-2) is an enzyme with systematic name S-adenosyl-L-methionine:squalene C-methyltransferase. This enzyme catalyses the following chemical reaction

2 S-adenosyl-L-methionine + squalene ⇌ 2 S-adenosyl-L-homocysteine + 3,22-dimethyl-1,2,23,24-tetradehydro-2,3,22,23-tetrahydrosqualene (overall reaction)(1a) S-adenosyl-L-methionine + squalene ⇌ S-adenosyl-L-homocysteine + 3-methyl-1,2-didehydro-2,3-dihydrosqualene(1b) S-adenosyl-L-methionine + 3-methyl-1,2-didehydro-2,3-dihydrosqualene ⇌ S-adenosyl-L-homocysteine + 3,22-dimethyl-1,2,23,24-tetradehydro-2,3,22,23-tetrahydrosqualene

There are two isoforms in the green alga Botryococcus braunii BOT22 that differ in their specificity .