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Metabolism

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Folic acid occurs within the diet mainly as a polyglutamate compound. The latter is digested by the enzyme pteroyl polyglutamate hydrolase on the small intestine brush border into dihydro- and tetrahydrofolates. These substrates are kept in a reduced state by the presence of ascorbic acid.

Folate metabolites are absorbed into enterocytes by two key means:

  • at physiological concentrations, by an active transport mechanism; the specific transporter is also used by the drug methotrexate
  • at supraphysiological concentrations, by passive diffusion; this is the route taken by the majority of folate supplements

Cobalamin within cells is important for producing the metabolite tetrahydrofolate. Tetrahydrofolate is the metabolically active form of folate.

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