A study of the uptake and degradation of folic acid, citrovorum factor, aminopterin, and pyrimethamine by bacteria.

In the course of a study of the mechanism of action of the antimalarial drug pyrimethamine (Daraprim (Burroughs Wellcome) ; 2,4-diamino-5-p-chlorophenyll6ethyl pyrimidine) (1)) it was observed that cells of Streptococcus jaecalis took up and stored the drug and that glucose greatly inhibited this uptake. When similar experimental conditions were employed for a study of the uptake of folic acid and leucovorin (.V5-formyl-5) 6,7, %tetrahydrofolic acid) by cells of Streptococcus jaecalis, it was observed that glucose is essential for both the accumulation and degradation of these vitamins (2). Since nothing appears to be known regarding the mechanism for cellular penetration by these vitamins, a more intensive study of the factors influencing their uptake and degradation was undertaken. There have been several investigations of the uptake of some other vitamins by bacteria. McIlwain and Hughes (3) found that glucose is essential for the accumulation of pantothenic acid by suspensions of hemolytic streptococci. Oginsky (4) described the uptake of vitamin Blz by Escherichia coli. Glucose did not seem to be essential in this case. Lichstein and Ferguson (5) reported that cells of Lactobacillus arabinosus assimilate biotin more efficiently in the presence of glucose. A number of investigators have studied the degradation of folic acid and citrovorum factor (formyltetrahydrofolic acid). Woods (6) reported on the work of Lilienthal who found that Lactobacillus casei degrades all but about 1 per cent of proffered folic acid, and this occurs best in the presence of glucose. The remaining 1 per cent was converted to citrovorum factor. Several other investigators (7-9) have demonstrated the degradation of folic acid and citrovorum factor by liver. A diazotizable amine is produced during the reaction, probably due to the spontaneous decomposition of the product, tetrahydrofolic acid, to p-aminobenzoylglutamic acid and a pteridine. Braganca and Krishnamurthy (10) found the degradation of folic acid by human erythrocytes to be due to a peroxidase. This paper describes the accumulation and degradation of folic acid and leucovorin by various species of bacteria under several sets of experimental conditions. The antifolic acid drugs pyrimethamine and aminopterin have been investigated in a similar manner. The results suggest that the vitamins and their structural analogue, aminopterin, may enter the cell by means of an active transport mechanism, whereas pyrimethamine probably enters by passive diffusion.