During the 1st hr after feeding folic acid—3H (3H-PteGlu) to fasting human volunteers, plasma S. faecalis and 3H activity were elevated to an equivalent degree, whereas after this, the 3H activity exceeded S. faecalis activity, which suggests gradual conversion of folic acid—3H to methyltetrahydrofolate-3H (5-CH3H4 PteGlu). The increase of L. casei activity exceeded the increase of S. faecalis and 3H activity, which is consistent with flushing of endogenous methyltetrahydrofolate from the tissues by the administered folic acid—3H. Feeding of 5-formyltetrahydrofolate (±5CHOH4PteGlu) produced a large increase of plasma L. casei activity and only a slight increase of S. faecalis and P. cerevisiae activity, which is consistent with very rapid conversion of folinic acid to methyltetrahydrofolate.


Roy F. Pratt, Bernard A. Cooper


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