Biochemical studies with the "citrovorum factor".

Abstract

Abstract Normal adult males were given pteroylglutamic acid (PGA) or leucovorin (a synthetic substance having the activity of citrovorum factor [CF] under varying conditions and the urinary excretion of CF was measured by microbiological assay. The average CF content of normal urine was somewhat less than 0.001γ/ml. As judged by six-hour urinary excretion, 0.1 per cent of an orally administered dose of 50 mg. of PGA was converted to CF. About a three-fold higher level of CF was excreted if 1 Gm. ascorbic acid was taken simultaneously with 50 mg. PGA. When leucovorin was taken orally only 1.1 per cent of the CF activity of the dose was recovered in the urine. This recovery was not increased by the simultaneous ingestion of ascorbic acid. When leucovorin was taken by injection 22 per cent of the activity was recovered in the urine. When liver homogenate from PGA deficient rats was incubated in the presence of PGA a marked increase in the amount of CF formed was noted on the addition of ascorbic acid. However, leucovorin failed to alleviate a dietary deficiency of ascorbic acid in guinea pigs.