ExplorEnz: EC 2.1.1.13

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2.1.1.13

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 1.16.1.8, [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 1.18.1.2, ferredoxin—NADP⁺ reductase). Acts on the monoglutamate as well as the triglutamate folate, in contrast with EC 2.1.1.14, 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

References:

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 2.1.1.13 created 1972, modified 2003]