edit ] Regeneration of methionine Methionine can be regenerated from homocysteine via (4) methionine synthase in a reaction that requires Vitamin B 12 as a cofactor . Homocysteine can also be remethylated using glycine betaine (NNN-trimethyl glycine, TMG) to methionine via the enzyme betaine-homocysteine methyltransferase (E.C.2.1.1.5, BHMT). BHMT makes up to