Growth Inhibition in Tetrahymena by Folic Acid Analogs.

Summary The antifolics, 4-amino-9-methylpteroylglutamic acid (A-ninopterin), 4-amino-10-methylpteroylglutamic acid (A-methopterin) and 4-amino-9;10-dimethyl-pteroylglutamic acid (A-denopterin) are all inhibitory to Tetrahymena. The inhibition produced by A-ninopterin is strictly competitive, being released over wide ranges of concentration of folic acid. The inhibition indices of the other two analogs decrease as the amount of folic acid in the medium increases until a certain level is reached, at which they become constant. This shifting index is tentatively explained on the basis of the ability of Tetrahymena to deaminate the 4-position of the analogs.