Thie Pteroylglutamate Components of American Diets

Folic acid activity, as determined by conventional bacteriological assay procedures, reflects the presence of a number of compounds other than pteroylglutamic acid (PGA). For example, one popular test organism, Streptococcus fecalis, will show a growth response in folic acid free medium to at least ten derivatives of PGA in addition to thymine, hypoxanthine, theobromine, guanidine, uric acid, and several other related compounds (1). Another organism, Lactobacillus casei, shows growth with a somewhat wider range of PGA derivatives, including both methylated and triglutamate forms that do not support growth of S. fecalis (2). Under these circumstances, the practice of expressing the growth-supporting ability of crude dietary materials in terms of a single reference standard may not give a true indication of the PGA content of foods, because food may contain a mixture of compounds with folic acidlike activity (3). Nevertheless, most dietary tables on the folic acid content of foods are based on such assays. The discrepancy between the amount of folic acid activity in diets and the amount of pure PGA required for the treatment of tropical sprue has led to the suggestion that humans may have a specific requirement for PGA (3). It therefore seemed important to assess the quantity of PGA available in the unsubstituted form from ordinary foods and to investigate the amount of folic acidlike activity that is present in forms other than pure PGA. A method has been employed in which factors with folic acid-like activity are chemically