The activity of dihydrofolate reductase varies greatly among individuals. The main form of folate in plasma is 5-MTHF.
Before entering the bloodstream, the enzyme dihydrofolate reductase reduces the monoglutamate form to THF and converts it to either methyl or formyl forms. Passive diffusion also occurs when pharmacological doses of folic acid are consumed. When consumed, food folates are hydrolyzed to the monoglutamate form in the gut prior to absorption by active transport across the intestinal mucosa. An impairment of this reaction initiates a process that can lead to megaloblastic anemia, one of the hallmarks of folate deficiency. Another folate-dependent reaction, the methylation of deoxyuridylate to thymidylate in the formation of DNA, is required for proper cell division. One of the most important folate-dependent reactions is the conversion of homocysteine to methionine in the synthesis of S-adenosyl-methionine, an important methyl donor. Some dietary supplements also contain folate in the monoglutamyl form, 5-MTHF (also known as L-5-MTHF, 5-methyl-folate, L-methylfolate, and methylfolate).įolate functions as a coenzyme or cosubstrate in single-carbon transfers in the synthesis of nucleic acids (DNA and RNA) and metabolism of amino acids. Folic acid is the fully oxidized monoglutamate form of the vitamin that is used in fortified foods and most dietary supplements. Food folates are in the tetrahydrofolate (THF) form and usually have additional glutamate residues, making them polyglutamates. “Folate,” formerly known as “folacin” and sometimes “vitamin B9,” is the generic term for naturally occurring food folates, and folates in dietary supplements and fortified foods, including folic acid.
Introductionįolate is a water-soluble B vitamin that is naturally present in some foods, added to others, and available as a dietary supplement. For a general overview of Folate, see our consumer fact sheet on Folate. This is a fact sheet intended for health professionals.
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