In enzymology, a tetrahydromethanopterin S-methyltransferase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are 5-methyl-5,6,7,8-tetrahydromethanopterin and 2-mercaptoethanesulfonate (coenzyme M), whereas its two products are 5,6,7,8-tetrahydromethanopterin and 2-(methylthio)ethanesulfonate.
This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is 5-methyl-5,6,7,8-tetrahydromethanopterin:2-mercaptoethanesulfonate 2-methyltransferase. This enzyme is also called tetrahydromethanopterin methyltransferase. This enzyme participates in folate biosynthesis.