5-Methyltetrahydrofolate-homocysteine methyltransferase

5-Methyltetrahydrofolate-homocysteine methyltransferase or (MTR) is an enzyme responsible for the production of methionine from homocysteine. MTR forms part of the S-adenosyl methionine cycle and is also called methionine synthase.

Function
MTR contains the cofactor - methylcobalamin (MeB12) and uses the substrates N5-methyl-tetrahydrofolate (N5-methyl-THF) and homocysteine.

The enzyme works in two steps in a ping-pong reaction. First, methylcobalamin is formed by a methyl group transfer from N5-mTHF with formation of MeB12 and tetrahydrofolate (THF). In the second step, MeB12 transfers this methyl group to (homocysteine), regenerating the cofactor cobalamin and releasing the product methionine