484 THE BIOCHEMISTRY OF B VITAMINS 



easily to p-aminobenzoic acid by oxidation, reduction or hydrolytic reac- 

 tions. However, there is no such explanation for the activity of several 

 compounds which apparently may be utilized as such in carrying out the 

 biochemical functions of the growth factor. Among these are 2-fluoro-4- 

 aminobenzoic acid 21 and the corresponding 2-bromocompound, 21 as well 

 as 2-aminopyrimidine-5-carboxylic acid. 31 



COOH 



I 



N 



NH 2 NH 2 



2-fluoro-J f .-aminobenzoic acid 2-aminopyrimidine-5-carboxylic acid 



2-Fluoro-4-aminobenzoic acid is reported by Wyss, Rubin and Strands- 

 kov 21 to be approximately 38 per cent as effective as p-aminobenzoic 

 acid in promoting growth of either Clostridium acetobutylicum or a 

 mutant strain of Neurospora crassa requiring p-aminobenzoic acid for 

 growth, and has approximately this same relative activity /38 per cent) 

 in preventing the toxicity of sulfanilamide for Escherichia coli. Since the 

 ratio of sulfanilamide to 2-fluoro-4-aminobenzoic acid is indicated to be 

 constant over a range of concentrations, the utilization of the analogue as 

 such in building the appropriate coenzyme is indicated. If conversion to 

 p-aminobenzoic acid were the mechanism of action, the per cent conver- 

 sion would be expected to decrease with increased concentration of the 

 analogue. 



2-Hydroxy-4-aminobenzoic acid (4-aminosalicylic acid) is particularly 

 interesting. Though this compound appears to inhibit effectively the 

 utilization of p-aminobenzoic acid in Mycobacterium tubercidosis* 1 ' 42 

 it does not have such an action in a wide variety of other organisms 

 (p. 525) . On the contrary, for two mutant strains of Escherichia coli 

 which require p-aminobenzoic acid, the hydroxy derivative is 4 to 16 

 per cent as effective as p-aminobenzoic acid in promoting growth. 28 Thus, 

 the analogue replaces p-aminobenzoic acid in promoting growth of one 

 organism and inhibits the functioning of this factor in another organism. 



The activity of p-nitrobenzoic acid varies considerably. It is almost 

 inactive in preventing the toxicity of sulfanilamide for Streptococcus 

 hemolyticus, but is almost as effective as p-aminobenzoic acid in promot- 

 ing growth of some strains of Clostridium acetobutylicum. The nitro 

 compound is only slightly active for a "p-aminobenzoicless" strain of 

 Neurospora crassa, 24 and inhibits the growth of Streptococcus viridans 43 

 (p. 522). The growth inhibition is prevented by p-aminobenzoic acid or 



