646 THE BIOCHEMISTRY OF B VITAMINS 



L-Carnosine is approximately one-fourth as active as /3-alanine for a 

 strain of diphtheria bacillus " and for Saccharomyces cerevisiae, Fleisch- 

 mann's strain 139, 100 but is not active for Saccharomyces cerevisiae 

 G. M. 30 D-Carnosine was inactive for the diphtheria bacillus. 



The inhibitory effect of propionic acid for Escherichia coli, 101 for Sac- 

 charomyces cerevisiae, 102 and to some extent for Acetobacter suboxy- 

 dans, 102 is prevented by ^-alanine. For Saccharomyces cerevisiae the 

 inhibition index is approximately 10,000. Pantothenic acid completely 

 reverses the toxicity at its minimum effective concentration so that it 

 appears that propionic acid also prevents the conversion of ,/3-alanine to 

 pantothenic acid in these organisms. Acetic acid acts in an analogous 

 manner with this strain of yeast, but is much less effective. 



Analogues of Pantoic Acid. Compounds structurally similar to pantoic 

 acid and possessing growth inhibiting properties are listed in Table 34. 

 However, these compounds are not necessarily competitive antagonists 

 of pantoic acid. On the contrary, most of them cannot be considered 

 solely as competitive inhibitors of the functioning of pantoic acid. 



Thus, a group of pantoic acid analogues reported by Cheldelin and 

 Schink 14 prevent the growth of Acetobacter suboxydans either in the 

 presence of pantothenic acid or pantoic acid as indicated in Table 34. 

 However, growth of Saccharomyces cerevisiae G. M. stimulated by panto- 

 thenic acid was not prevented by either a-hydroxy-/3,/?-dimethylbutyric 

 acid or /?,y-dihydroxy-/3-methylbutyric acid, but the growth stimulated 

 by /^-alanine was prevented by the analogues. This suggests that the two 

 analogues prevent the biosynthesis of pantothenic acid in the yeast under 

 these conditions, presumably by competition with pantoic acid or a related 

 metabolite. With Acetobacter suboxydans the analogues appear to prevent 

 the utilization of pantothenic acid rather than its synthesis. 



Ivanovics 103 has reported that salicylic acid at low concentrations 

 appears to prevent the synthesis of pantothenic acid in Escherichia coli. 

 This effect is exerted to a lesser extent by acetylsalicylic acid or phenyl- 

 salicylate but not by thiosalicylic acid or salicylamide. The inhibitory 

 action of low concentrations of salicylic acid was prevented in a somewhat 

 noncompetitive manner by pantothenic acid. Also, larger amounts of 

 pantoic acid as well as some amino acids were effective in preventing the 

 toxicity. Although valine alone was singly the most active of the amino 

 acids, mixtures of methionine with valine, leucine, isoleucine, or lysine 

 were more effective. These mixtures were almost equivalent to a casein 

 hydrolysate which caused an eight fold increase in pantothenic acid syn- 

 thesis. Thiamine and vitamin K have also been reported to prevent par- 

 tially the inhibitory effect of salicylic acid. 104 



Pantoic acid is approximately nine times more active than pantolactone 



