Reaction: 5-methyltetrahydrofolate + L-homocysteine = tetrahydrofolate + L-methionine
For diagram of reaction click here and mechanism click here.
Other name(s): 5-methyltetrahydrofolatehomocysteine S-methyltransferase; 5-methyltetrahydrofolatehomocysteine transmethylase; N-methyltetrahydrofolate:L-homocysteine methyltransferase; N5-methyltetrahydrofolate methyltransferase; N5-methyltetrahydrofolatehomocysteine cobalamin methyltransferase; N5-methyltetrahydrofolichomocysteine vitamin B12 transmethylase; B12 N5-methyltetrahydrofolate homocysteine methyltransferase; methyltetrahydrofolatehomocysteine 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 22.214.171.124, [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 126.96.36.199, ferredoxinNADP+ reductase). Acts on the monoglutamate as well as the triglutamate folate, in contrast with EC 188.8.131.52, 5-methyltetrahydropteroyltriglutamatehomocysteine S-methyltransferase, which acts only on the triglutamate.
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, PDB, CAS registry number: 9033-23-2
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