Methylcobalamin Explained

Methylcobalamin (mecobalamin, MeCbl, or MeB) is a cobalamin, a form of vitamin B. It differs from cyanocobalamin in that the cyano group at the cobalt is replaced with a methyl group.[1] Methylcobalamin features an octahedral cobalt(III) centre and can be obtained as bright red crystals. From the perspective of coordination chemistry, methylcobalamin is notable as a rare example of a compound that contains metal–alkyl bonds. Nickel–methyl intermediates have been proposed for the final step of methanogenesis.

Methylcobalamin is equivalent physiologically to vitamin B,[2] and can be used to prevent or treat pathology arising from a lack of vitamin B intake (vitamin B12 deficiency).

Methylcobalamin is also used in the treatment of peripheral neuropathy, diabetic neuropathy, and as a preliminary treatment for amyotrophic lateral sclerosis.[3]

Methylcobalamin that is ingested is not used directly as a cofactor, but is first converted by MMACHC into cob(II)alamin. Cob(II)alamin is then later converted into the other two forms, adenosylcobalamin and methylcobalamin for use as cofactors. That is, methylcobalamin is first dealkylated and then regenerated.[4] [5] [6]

According to one author, it is important to treat vitamin B deficiency with hydroxocobalamin or cyanocobalamin or a combination of adenosylcobalamin and methylcobalamin, and not methylcobalamin alone.[7] __TOC__

Production

Methylcobalamin can be produced in the laboratory by reducing cyanocobalamin with sodium borohydride in alkaline solution, followed by the addition of methyl iodide.[8]

Functions

This vitamer, along with adenosylcobalamin, is one of two active coenzymes used by vitamin B-dependent enzymes and is the specific vitamin B form used by 5-methyltetrahydrofolate-homocysteine methyltransferase (MTR), also known as methionine synthase. Methylcobalamin participates in the Wood-Ljungdahl pathway, which is a pathway by which some organisms utilize carbon dioxide as their source of organic compounds. In this pathway, methylcobalamin provides the methyl group that couples to carbon monoxide (derived from CO2) to afford acetyl-CoA. Acetyl-CoA is a derivative of acetic acid that is converted to more complex molecules as required by the organism.[9]

Methylcobalamin is produced by some bacteria. It plays an important role in the environment, where it is responsible for the biomethylation of certain heavy metals. For example, the highly toxic methylmercury is produced by the action of methylcobalamin. In this role, methylcobalamin serves as a source of "CH3+".

A lack of cobalamin can lead to megaloblastic anemia and subacute combined degeneration of the spinal cord.[10]

See also

Notes and References

  1. Book: Vitamins in animal and human nutrition . McDowell LR . Booksgoogle.com. 28 January 2018. 978-0813826301 . 2000 . Wiley .
  2. Sil A, Kumar H, Mondal RD, Anand SS, Ghosal A, Datta A, Sawant SV, Kapatkar V, Kadhe G, Rao S . A randomized, open labeled study comparing the serum levels of cobalamin after three doses of 500 mcg vs. a single dose methylcobalamin of 1500 mcg in patients with peripheral neuropathy . The Korean Journal of Pain . 31 . 3 . 183–190 . July 2018 . 30013732 . 6037815 . 10.3344/kjp.2018.31.3.183 .
  3. Web site: Eisai Submits New Drug Application for Mecobalamin Ultra-High Dose Preparation as Treatment for Amyotrophic Lateral Sclerosis in Japan . Eisai.com . 28 January 2018 .
  4. Kim J, Hannibal L, Gherasim C, Jacobsen DW, Banerjee R . A human vitamin B12 trafficking protein uses glutathione transferase activity for processing alkylcobalamins . The Journal of Biological Chemistry . 284 . 48 . 33418–33424 . November 2009 . 19801555 . 2785186 . 10.1074/jbc.M109.057877 . free .
  5. Hannibal L, Kim J, Brasch NE, Wang S, Rosenblatt DS, Banerjee R, Jacobsen DW . Processing of alkylcobalamins in mammalian cells: A role for the MMACHC (cblC) gene product . Molecular Genetics and Metabolism . 97 . 4 . 260–266 . August 2009 . 19447654 . 2709701 . 10.1016/j.ymgme.2009.04.005 .
  6. Froese DS, Gravel RA . Genetic disorders of vitamin B₁₂ metabolism: eight complementation groups–eight genes . Expert Reviews in Molecular Medicine . 12 . e37 . November 2010 . 21114891 . 2995210 . 10.1017/S1462399410001651 .
  7. Thakkar K, Billa G . Treatment of vitamin B12 deficiency – Methylcobalamine? Cyancobalamine? Hydroxocobalamin? – clearing the confusion . European Journal of Clinical Nutrition . 69 . 1 . 1–2 . January 2015 . 25117994 . 10.1038/ejcn.2014.165 . free .
  8. Book: David, Dophin . Vitamins and Coenzymes . Preparation of the Reduced Forms of Vitamin B12 and of Some Analogs of the Vitamin B12 Coenzyme Containing a Cobalt-Carbon Bond. McCormick DB, Wright LD . Methods in Enzymology . 18 . 34–54. January 1971. 10.1016/S0076-6879(71)18006-8 . Academic Press . 9780121818821 .
  9. Fontecilla-Camps JC, Amara P, Cavazza C, Nicolet Y, Volbeda A . Structure-function relationships of anaerobic gas-processing metalloenzymes . Nature . 460 . 7257 . 814–822 . August 2009 . 19675641 . 10.1038/nature08299 . 2009Natur.460..814F . 4421420 .
  10. Book: Bémeur C, Montgomery JA, Butterworth RF . Vitamins Deficiencies and Brain Function . 103-124 (112) . Blass JP . Neurochemical Mechanisms in Disease . Advances in Neurobiology . 2011 . 1 . 10.1007/978-1-4419-7104-3_4 . 978-1-4419-7103-6 .

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