title: Intestinal transport of 5-methyltetrahydrofolate.
abstract: The mechanism of intestinal absorption of 5-methyltetrahydrofolate (5- CH3THF ) has been the topic of some controversy. In the present study, we have used enzymatically prepared 5- CH3THF to characterize transport by rat intestinal loops in vivo and everted jejunal sacs in vitro. Transport of 5- CH3THF is saturable (Km = 5.2 microM) and highly pH dependent, with the rate of maximal transport occurring at pH 5.8. Transport is competitively inhibited by folic acid (Ki = 4.2 microM) and methotrexate (Ki = 4.65 microM). Metabolic poisons and anaerobiosis greatly reduce 5- CH3THF transport. We conclude that 5- CH3THF transport in the rat intestine occurs by the same structure-specific mechanism responsible for the transport of unreduced folic acid and other monoglutamyl folates.
mesh_terms: D000818:Animals; D005492:Folic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000378:metabolism; D007583:Jejunum / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013763:Tetrahydrofolates / Q000138:chemical synthesis / Q000378:metabolism*; D014316:Tritium
chemical_list: D013763:Tetrahydrofolates; D014316:Tritium; D005492:Folic Acid; C005984:5-methyltetrahydrofolate