folate

(= tetrahydrofolate)

Molecule that acts as a carrier of one-carbon units in intermediary metabolism. It contains residues of p -aminobenzoate, glutamate, and a substituted pteridine. The latter cannot be synthesized by mammals, which must obtain tetrahydrofolate as a vitamin or from intestinal microorganisms. One-carbon units are carried at three different levels of oxidation, as methyl-, methylene- or formimino- groups. Important biosyntheses dependent on tetrahydrofolate include those of methionine, thymine and purines. Analogues of dihydrofolate, such as aminopterin and methotrexate block the action of tetrahydrofolate by inhibiting its regeneration from dihydrofolate.