The Enzyme Database

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Accepted name: methionine synthase
Reaction: 5-methyltetrahydrofolate + L-homocysteine = tetrahydrofolate + L-methionine
For diagram of reaction, click here
Other name(s): 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; methyltetrahydrofolate—homocysteine vitamin B12 methyltransferase; tetrahydrofolate methyltransferase; tetrahydropteroylglutamate methyltransferase; tetrahydropteroylglutamic methyltransferase; vitamin B12 methyltransferase; cobalamin-dependent methionine synthase; methionine synthase (cobalamin-dependent); MetH
Systematic name: 5-methyltetrahydrofolate:L-homocysteine S-methyltransferase
Comments: 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: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 9033-23-2
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 (1969) 228–234. [DOI] [PMID: 5799642]
2.  Foster, M.A., Dilworth, M.J. and Woods, D.D. Cobalamin and the synthesis of methionine by Escherichia coli. Nature 201 (1964) 39–42. [PMID: 14085561]
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 (1964) 497–504. [PMID: 5319972]
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 (1964) 2888–2895. [PMID: 14216440]
5.  Taylor, R.T. Escherichia coli B N 5 -methyltetrahydrofolate-homocysteine cobalamin methyltransferase: gel-filtration behavior of apoenzyme and holoenzymes. Biochim. Biophys. Acta 242 (1971) 355–364. [DOI] [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 (1998) 5372–5382. [DOI] [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 (1998) 8410–8416.
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 (2000) 10711–10719. [DOI] [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 (2002) 53–56. [DOI] [PMID: 11731805]
[EC created 1972, modified 2003]

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