IUBMB Enzyme Nomenclature


Accepted name: [methionine synthase] reductase

Reaction: 2 [methionine synthase]-methylcob(III)alamin + 2 S-adenosyl-L-homocysteine + NADP+ = 2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine

For diagram of reaction, click here

Other name(s): methionine synthase cob(II)alamin reductase (methylating); methionine synthase reductase; [methionine synthase]-cobalamin methyltransferase (cob(II)alamin reducing); [methionine synthase]-methylcob(I)alamin,S-adenosylhomocysteine:NADP+ oxidoreductase

Systematic name: [methionine synthase]-methylcob(III)alamin,S-adenosyl-L-homocysteine:NADP+ oxidoreductase

Comments: In humans, the enzyme is a flavoprotein containing FAD and FMN. The substrate of the enzyme is the inactivated cobalt(II) form of EC, methionine synthase. Electrons are transferred from NADPH to FAD to FMN. Defects in this enzyme lead to hereditary hyperhomocysteinemia.

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 207004-87-3


1. Leclerc, D., Wilson, A., Dumas, R., Gafuik, C., Song, D., Watkins, D., Heng, H.H.Q., Rommens, J.M., Scherer, S.W., Rosenblatt, D.S., Gravel, R.A. Cloning and mapping of a cDNA for methionine synthase reductase, a flavoprotein defective in patients with homocystinuria. Proc. Natl. Acad. Sci. USA 95 (1998) 3059-3064. [PMID: 9501215]

2. Olteanu, H. and Banerjee, R. Human methionine synthase reductase, a soluble P-450 reductase-like dual flavoprotein, is sufficient for NADPH-dependent methionine synthase activation. J. Biol. Chem. 276 (2001) 35558-35563. [PMID: 11466310]

3. Olteanu, H., Munson, T. and Banerjee, R. Differences in the efficiency of reductive activation of methionine synthase and exogenous electron acceptors between the common polymorphic variants of human methionine synthase reductase. Biochemistry 41 (2002) 13378-13385. [PMID: 12416982]

[EC created 1999 as EC, transferred 2003 to EC, modified 2020]

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