. The Biochemistry of B vitamins. Vitamins; Vitamin B complex. 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 COOH I. N NH2 NH2 acid 2-aminopyrimidine-5-carboxylic acid 2-Fluoro-4-amin
. The Biochemistry of B vitamins. Vitamins; Vitamin B complex. 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 COOH I. N NH2 NH2 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 Thus, the analogue replaces p-aminobenzoic acid in promoting growth of one organism and inhibits the functioning of this factor in a
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