methionine synthase;
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

Transferases;
Transferring one-carbon groups;
Methyltransferases

5-methyltetrahydrofolate:L-homocysteine S-methyltransferase

5-methyltetrahydrofolate + L-homocysteine = tetrahydrofolate + L-methionine [RN:R00946]

R00946;
(other) R09365

5-methyltetrahydrofolate [CPD:C00440];
L-homocysteine [CPD:C00155]

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.