The effect of ascorbic acid on the enzymatic formation of the citrovorum factor.

May and coworkers (l-3) demonstrated that the production of a scorbutic state in monkeys led to the development of a megaloblastic anemia, a condition which responded promptly to treatment with pteroylglutamic acid (PGA) or to very much smaller amounts of synthetic citrovorum factor (leucovorin or folinic acid-SF) .I It has been shown that the administration of ascorbic acid to normal human subjects ingesting PGA caused a 3-fold increase in the amount of citrovorum factor (CF) excreted in the urine (4-6). Also, scorbutic patients were shown to excrete little or no CF in the urine when given similar test doses of PGA, even though absorption of the substance was apparently normal (6) ; the excretion of significant amounts of CF occurred only after prolonged treatment with ascorbic acid (6, 7). Nichol and Welch (8) reported that the formation of CF by slices of rat liver incubated in a medium containing PGA was augmented by the presence of ascorbic acid. Finding conditions suitable for the activity of this system in cell-free preparations of liver (9) has made possible a more detailed study of the effect of ascorbic acid on the enzymatic formation from PGA of compounds which, unlike PGA, promote the rapid growth of Leuconostoc citrovorum.