Further Studies on Effect of Folic Acid Analogs on Growth of Tetrahymena

Summary 1. The growth of Tetrahymena pyrijormis, which was produced when amino-pterin was added to a folic-acid deficient medium, was due to the presence of folic acid in the aminopterin. 2. A similar contamination may explain the replacement effects of pter-oyl-D-glutamic acid and 4-dimethylamino-pteroylglutamic acid. 3. Folic acid is spared by a number of folic acid analogs in which the glutamic acid is replaced by other amino acids. 4. These compounds cannot serve as sources of amino acids. 5. Of several 3′, 5′-dichloro-substituted folic acid analogs, the most inhibitory is 3′, 5′-dichloro-N10-methylpteroylglu-tamic acid. 6. It is suggested that this compound may also be effective in inhibiting aminopterin-resistant cells.