Labile citrovorum factor in urine.

The isolation of N10 formylfolic acid' from natural materials has been reported by several groups of workers (Rauen et al., 1952; Rauen and Jaenicke, 1953; Greenberg, 1954a; Silverman et al., 1954). It was concluded that the compound had been derived either from the degradation of a labile intermediate involved in the conversion of a bound (microbiologically inactive) form of folic acid in liver to citrovorum factor (CF) or from a biosynthetically prepared transformylation cofactor. These observations have taken on added significance since Greenberg has shown recently that N10 formyltetrahydrofolic acid or a closely related compound (anhydrocitrovorum factor in which the one carbon unit is linked in a 5 to 10 bridge) can donate its formyl group to 4-amino-5-imidazolecarboxamide ribotide (Greenberg, 1954b and per8onal communication). Dr. Greenberg kindly supplied us with several synthetic samples of such reduced and formylated derivatives of folic acid. These possessed varying degrees of citrovorum factor activity which disappeared if the samples were stored for several hours at room temperature or were subjected to autoclaving. The lability of the active samples suggested that if such forms occurred naturally they might not have been detected because of their great instability. We undertook the search for such compounds and wish to describe the occurrence and some properties of a labile compound in urine which possesses growth activity for Leuconostoc citrovorum. This factor differs from CF in that it is destroyed during normal autoclaving procedures in the absence of reducing agents.