EC - Methionine synthase

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IntEnz Enzyme Nomenclature


Accepted name:
methionine synthase
Other names:
5-methyltetrahydrofolate—homocysteine S-methyltransferase
5-methyltetrahydrofolate—homocysteine transmethylase
N-methyltetrahydrofolate:L-homocysteine methyltransferase
N5-methyltetrahydrofolate methyltransferase
N5-methyltetrahydrofolate—homocysteine cobalamin methyltransferase
N5-methyltetrahydrofolic—homocysteine vitamin B12 transmethylase
B12 N5-methyltetrahydrofolate homocysteine methyltransferase
cobalamin-dependent methionine synthase
methionine synthase (cobalamin-dependent)
methionine synthetase
methyltetrahydrofolate—homocysteine vitamin B12 methyltransferase
tetrahydrofolate methyltransferase
tetrahydropteroylglutamate methyltransferase
tetrahydropteroylglutamic methyltransferase
vitamin B12 methyltransferase
Systematic name:
5-methyltetrahydrofolate:L-homocysteine S-methyltransferase




Contains zinc and cobamide. The enzyme becomes inactivated occasionally during its cycle by oxidation of Co(I) to Co(II). Reactivation by reductive methylation is catalysed by the enzyme itself, with S-adenosyl-L-methionine as the methyl donor and a reducing system. For the mammalian enzyme, the reducing system involves NADPH and EC, [methionine synthase] reductase. In bacteria, the reducing agent is flavodoxin, and no further catalyst is needed (the flavodoxin is kept in the reduced state by NADPH and EC, ferredoxin—NADP+ reductase). Acts on the monoglutamate as well as the triglutamate folate, in contrast with EC, 5-methyltetrahydropteroyltriglutamate—homocysteine S-methyltransferase, which acts only on the triglutamate.

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , DIAGRAM , DIAGRAM , DIAGRAM , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Protein domains and families: PROSITE:PDOC50972
Structural data: CSA , EC2PDB
Gene Ontology: GO:0008705
CAS Registry Number: 9033-23-2
UniProtKB/Swiss-Prot: (21) [show] [UniProt]


  1. Burton, E.G. and Sakami, W.
    The formation of methionine from the monoglutamate form of methyltetrahydrofolate by higher plants.
    Biochem. Biophys. Res. Commun. 36 : 228-234 (1969). [PMID: 5799642]
  2. Foster, M.A., Dilworth, M.J. and Woods, D.D.
    Cobalamin and the synthesis of methionine by Escherichia coli.
    Nature 201 : 39-42 (1964).
  3. Guest, J.R., Friedman, S., Foster, M.A., Tejerina, G. and Woods, D.D.
    Transfer of the methyl group from N5-methyltetrahydrofolates to homocysteine in Escherichia coli.
    Biochem. J. 92 : 497-504 (1964).
  4. Loughlin, R.E., Elford, H.L. and Buchanan, J.M.
    Enzymatic synthesis of the methyl group of methionine. VII. Isolation of a cobalamin-containing transmethylase (5-methyltetrahydro-folate-homocysteine) from mammalian liver.
    J. Biol. Chem. 239 : 2888-2895 (1964).
  5. Taylor, R.T.
    Escherichia coli B N5-methyltetrahydrofolate-homocysteine cobalamin methyltransferase: gel-filtration behavior of apoenzyme and holoenzymes.
    Biochim. Biophys. Acta 242 : 355-364 (1971). [PMID: 4946148]
  6. Jarrett, J.T., Huang, S. and Matthews, R.G.
    Methionine synthase exists in two distinct conformations that differ in reactivity toward methyltetrahydrofolate, adenosylmethionine, and flavodoxin.
    Biochemistry 37 : 5372-5382 (1998). [PMID: 9548919]
  7. Peariso, K., Goulding, C.W., Huang, S., Matthews, R.G. and Penner-Hahn, J.E.
    Characterization of the zinc binding site in methionine synthase enzymes of Escherichia coli: The role of zinc in the methylation of homocysteine.
    J. Am. Chem. Soc. 120 : 8410-8416 (1998).
  8. Hall, D.A., Jordan-Starck, T.C., Loo, R.O., Ludwig, M.L. and Matthews, R.G.
    Interaction of flavodoxin with cobalamin-dependent methionine synthase.
    Biochemistry 39 : 10711-10719 (2000). [PMID: 10978155]
  9. Bandarian, V., Pattridge, K.A., Lennon, B.W., Huddler, D.P., Matthews, R.G. and Ludwig, M.L.
    Domain alternation switches B12-dependent methionine synthase to the activation conformation.
    Nat. Struct. Biol. 9 : 53-56 (2002). [PMID: 11731805]

[EC created 1972, modified 2003]