The urinary excretion of formic acid and formiminoglutamic acid in folic acid deficiency.

In previous investigations it was shown that in folic acid deficiency there is a large increase in the urinary excretion of formimino-n-glutamic acid (l-6). This increase has been explained by recent enzymatic studies demonstrating that the first step in the metabolism of formimino+glutamic acid is the transfer of the formimino group to tetrahydrofolic acid (7-9). Formimino-n-glutamic acid is an intermediate in histidine metabolism (10, 11)) and the urinary excretion of this compound in folic acid deficiency can be increased by the administration of n-histidine (3). Experiments with N16-labeled histidine demonstrated that the urinary formimino-n-glutamic acid was derived from histidine (3). In the present work we have demonstrated that, in addition to formimino-n-glutamic acid, there is a large increase in the excretion of formic acid in the urine of folic acid-deficient rats; in contrast to the results with formiminoglutamic acid, this formic acid is not derived from histidine. Our current studies have been facilitated by the recent development of sensitive spectrophotometric methods for the determination of formic acid (12) and formiminoglutamic acid (13).