metabolism
Last reviewed 06/2022
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.