(Methionine synthase) reductase

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[methionine synthase] reductase
EC number1.16.1.8
CAS number207004-87-3
IntEnzIntEnz view
ExPASyNiceZyme view
MetaCycmetabolic pathway
PDB structuresRCSB PDB PDBe PDBsum
Gene OntologyAmiGO / QuickGO

In enzymology, a [methionine synthase] reductase (EC is an enzyme that catalyzes the chemical reaction

2 [methionine synthase]-methylcob(I)alamin + 2 S-adenosylhomocysteine + NADP+ 2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine

The 3 products of this enzyme are methionine synthase-methylcob(I)alamin, S-adenosylhomocysteine, and NADP+, whereas its 4 substrates are methionine synthase-cob(II)alamin, NADPH, H+, and S-adenosyl-L-methionine.

Over time, the cob(I)alamin cofactor of methionine synthase becomes oxidized to cob(II)alamin rendering the enzyme inactive. Regeneration of functional enzyme requires reductive methylation via a reaction catalyzed by (methionine synthase) reductase in which S-adenosylmethionine is utilized as a methyl donor.[1]

This enzyme belongs to the family of oxidoreductases, to be specific those oxidizing metal ion with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is [methionine synthase]-methylcob(I)alamin,S-adenosylhomocysteine:NADP+ oxidoreductase. Other names in common use include methionine synthase cob(II)alamin reductase (methylating), methionine synthase reductase, [methionine synthase]-cobalamin methyltransferase (cob(II)alamin, and reducing). It employs one cofactor, flavoprotein.


  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. (1998-03-17). "Cloning and mapping of a cDNA for methionine synthase reductase, a flavoprotein defective in patients with homocystinuria". Proceedings of the National Academy of Sciences. 95 (6): 3059–3064. doi:10.1073/pnas.95.6.3059. ISSN 0027-8424. PMC 19694. PMID 9501215.
  • Olteanu H, Banerjee R (2001). "Human methionine synthase reductase, a soluble P-450 reductase-like dual flavoprotein, is sufficient for NADPH-dependent methionine synthase activation". J. Biol. Chem. 276 (38): 35558–63. doi:10.1074/jbc.M103707200. PMID 11466310.
  • Olteanu H, Munson T, Banerjee R (2002). "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 (45): 13378–85. doi:10.1021/bi020536s. PMID 12416982.