Explain the Absorption, Storage and Elimination of Folate?
Folic acid is readily absorbed from the small intestines through the portal vein and passed onto the tissues through general circulation. Naturally occurring food folate is converted into the monoglutamate form by the enzyme pteroylpolyglutarnate hydrolase or folate conjugase or glutamate carboxypeptidase II, located in the jejunal brush border membrane. After de conjugation, the monoglutaniyl folate is transported across the membrane by a pH-dependent carrier-mediated mechanism.
Folic acid once absorbed is acted upon by hepatic dihydrofolate reductase to convert to its metabolically active form which is tetrahydrofolic acid (THF). Following absorption, folic acid is largely reduced and methylated in the liver to 'N-5 methyltetrahydrofolic acid, which is the main transporting and storage form of folate in the body. Folate transport across membranes into cells in kidney, placenta and choroid plexus, occurs via membrane-associated folate binding proteins that act s folate receptors and facilitate cellular uptake of folate. Larger doses of folate may escape metabolism by the liver and appear in the blood mainly as folic acid.