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Vitamin B12 , folate, and the methionine remethylation cycle-biochemistry, pathways, and regulation.

  • Froese DS Division of Metabolism and Children's Research Center, University Children's Hospital, Zurich, Switzerland.
  • Fowler B Division of Metabolism and Children's Research Center, University Children's Hospital, Zurich, Switzerland.
  • Baumgartner MR Division of Metabolism and Children's Research Center, University Children's Hospital, Zurich, Switzerland.
  • 2019-01-30
Published in:
  • Journal of inherited metabolic disease. - 2019
folate
hyperhomocysteinemia
methionine cycle
methylmalonic acidemia
one-carbon metabolism
vitamin B12
5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase
Animals
Folic Acid
Folic Acid Deficiency
Humans
Methylmalonyl-CoA Mutase
Vitamin B 12
Vitamin B 12 Deficiency
English Vitamin B12 (cobalamin, Cbl) is a nutrient essential to human health. Due to its complex structure and dual cofactor forms, Cbl undergoes a complicated series of absorptive and processing steps before serving as cofactor for the enzymes methylmalonyl-CoA mutase and methionine synthase. Methylmalonyl-CoA mutase is required for the catabolism of certain (branched-chain) amino acids into an anaplerotic substrate in the mitochondrion, and dysfunction of the enzyme itself or in production of its cofactor adenosyl-Cbl result in an inability to successfully undergo protein catabolism with concomitant mitochondrial energy disruption. Methionine synthase catalyzes the methyl-Cbl dependent (re)methylation of homocysteine to methionine within the methionine cycle; a reaction required to produce this essential amino acid and generate S-adenosylmethionine, the most important cellular methyl-donor. Disruption of methionine synthase has wide-ranging implications for all methylation-dependent reactions, including epigenetic modification, but also for the intracellular folate pathway, since methionine synthase uses 5-methyltetrahydrofolate as a one-carbon donor. Folate-bound one-carbon units are also required for deoxythymidine monophosphate and de novo purine synthesis; therefore, the flow of single carbon units to each of these pathways must be regulated based on cellular needs. This review provides an overview on Cbl metabolism with a brief description of absorption and intracellular metabolic pathways. It also provides a description of folate-mediated one-carbon metabolism and its intersection with Cbl at the methionine cycle. Finally, a summary of recent advances in understanding of how both pathways are regulated is presented.
Language
  • English
Open access status
hybrid
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Persistent URL
https://folia.unifr.ch/global/documents/199163
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