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5-methyltetrahydrofolate-homocysteine methyltransferase

PDB rendering based on 2o2k.
Available structures
Symbols MTR; FLJ45386
External IDs OMIM156570 MGI894292 HomoloGene37280 GeneCards: MTR Gene
EC number
RNA expression pattern
PBB GE MTR 203774 at tn.png
More reference expression data
Species Human Mouse
Entrez 4548 238505
Ensembl ENSG00000116984 ENSMUSG00000021311
UniProt Q99707 n/a
RefSeq (mRNA) NM_000254 XM_138431
RefSeq (protein) NP_000245 XP_138431
Location (UCSC) Chr 1:
235.03 - 235.13 Mb
Chr 13:
12.27 - 12.31 Mb
PubMed search [1] [2]

5-Methyltetrahydrofolate-homocysteine methyltransferase (MTR, MTRR) or methionine synthase (MS, MeSe, MetH), is a human gene which codes for an enzyme of the same name.[1] The enzyme is responsible for the production of methionine from homocysteine. MTR forms part of the S-adenosylmethionine (SAMe) biosynthesis and regeneration cycle.[2]



MTR encodes the enzyme 5-methyltetrahydrofolate-homocysteine methyltransferase. This enzyme catalyzes the final step in methionine biosynthesis.[1] Mutations in MTR have been identified as the underlying cause of methylcobalamin deficiency complementation group G, or methylcobalamin deficiency cbl G type.[1]

MTR contains the cofactor methylcobalamin (MeB12) and uses the substrates N5-methyl-tetrahydrofolate (N5-mTHF) and homocysteine.

The enzyme works in two steps in a ping-pong reaction. First, methylcobalamin is formed by a methyl group transfer from N5-mTHF with formation of MeB12 and tetrahydrofolate (THF). In the second step, MeB12 transfers this methyl group to homocysteine, regenerating the cofactor cobalamin and releasing the product methionine.

The MTR reaction (click to enlarge)

MTR is the only mammalian enzyme that metabolizes 5-mTHF to regenerate the active cofactor, THF. Deficiency in MTR function may be due to genetic mutations, reduced levels of its cobalamin cofactor (vitamin B12), or decreased levels of the enzyme (methionine synthase) reductase (required for the sustained activity of MTR).

The consequence of reduced MTR activity is megaloblastic anemia.


Several polymorphisms in MTR have been identified.

  • 2756A→G (Asp919Gly)

See also


Further reading

External links



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