Factors affectinǵ the Requirement of Tetrahymena pyriformis (geleii) for Folic Acid

SUMMARY: In the use of an organism for assay of folic acid those compounds which affect the utilization of folic acid should be determined. With Tetrahymena pyriformis (geleii), it is shown that thymine (or thymidine), glycine, p-amino-benzoic acid, creatin and vitamin B12 diminish the requirement for folic acid. Pteroic acid, p-aminobenzoylglutamic acid, 5-methylcytosine, p-hydroxybenzoic acid, carbamylaspartic acid and ribonucleic acid have no effect on the requirement, while cholesterol and cortisone increase the requirement.