Experiments on the biological activities of various fractions of the folic acid antagonist "X-methyl" folic acid.

A crude synthetic preparation called crude "X-methyl" folate has previously been shown to function as a folate antagonist for rats and chicks. This product has been shown to contain two folate antagonists: 9-methyl folate, present as 6% by weight of the product and which has low activity as a folate antagonist for Streptococcus faecalis, and pyrrofolic acid, a compound present in small amounts (0.04%), but having high anti-folate biological activity for S. faecalis. These experiments deal with the antifolate activity of these two fractions for the rat as measured by their effects on histidine oxidation. Rats were fed a purified diet based on 20% vitamin-free casein and containing 1.0% sulfasuxidine. When this diet was supplemented with a marginal amount of folic acid (0.3 mg per kg diet), the addition of 4 g of crude antagonist decreased histidine oxidation and decreased liver folate levels. The addition of 240 mg of pure 9-methyl folic acid (amount of 9-methyl folic acid in 4 g of crude) produced similar decreases in histidine oxidation and liver folate levels. A concentrate of pyrrofolic acid (equivalent to 4 g of crude) free of 9-methyl folic acid produced no decrease in histidine oxidation and minimal changes in liver folate. This indicates that the folate antagonist activity observed previously with animals is probably due to the 9-methyl folic acid component rather than to the pyrrofolic acid activity.