PANTOTHENIC ACID 645 



N-butyryltaurine 68 and DL-N-a,y-dihydroxybutyryltaurine 68 are also 

 relatively inactive as inhibitors of pantothenic acid functioning. 



The two optically active forms of N-a-keto-/?-methyl-/3-methylol- 

 valeryltaurine are reported to have slight activity in inhibiting the growth 

 of Streptobacterium plantarum 105. 25 However, N-ct-keto-/3,/?-dimethyl-y- 

 hydroxybutyryltaurine does not show such an inhibitory effect. 87 



Analogues of ^-Alanine. The unintentional use of an inhibitor of the 

 utilization of /^-alanine led to the discovery of pantothenic acid as a 

 growth factor for yeast by Williams and co-workers. 29, 92 Asparagine 

 added to the medium prevented the response of yeast to /^-alanine and 

 allowed a very specific microbiological assay for the vitamin. 



Not only asparagine, which resembles /3-alanine structurally, but also 

 other a-amino acids in general prevent the utilization of /^-alanine by 

 yeast; 93,94 thus L-glutamic acid, L-aspartic acid, L-glutamine, glycine, 

 DL-alanine, DL-serine, DL-a-aminobutyric acid, DL-threonine, DL-norvaline, 

 DL-norleucine, dl- valine, DL-leucine, DL-methionine, and DL-cysteine show 

 an inhibitory effect on yeast growth stimulated by ^-alanine. However, 

 no such effect is obtained when growth is stimulated by pantothenic 

 acid, except for somewhat less specific inhibitions obtained only with 

 methionine and cysteine. 76 Proline, D-leucine, arginine, glycylglycine, 

 and a-aminoisobutyric acid do not inhibit growth stimulated by /?- 

 alanine. 



The more effective inhibitors of the utilization of /3-alanine have been 

 /?-amino acids. These include /3-aminobutyric acid, 95 isoserine, 96 and 

 phenyl-/?-alanine. 7G /3-Aminobutyric acid competitively inhibits the in- 

 crease in respiration of yeast brought about by /?-alanine when present 

 in the ratio 1000:1, but does not have any effect on the increase brought 

 about by the minimum effective concentration of pantothenic acid. 97 The 

 inhibitory effect on respiration which is paralleled by a similar effect on 

 growth is less if the analogue is added several hours after the /3-alanine. 

 Taurine, 95 /?-alanylglycine, 95 and N-methyl-/?-alanine 9G are ineffective 

 for this strain of yeast. Both taurine and pantoyltaurine have been found 

 to inhibit only one strain of yeast out of seventeen when growth was 

 stimulated by ^-alanine. 30 Taurine had no effect on growth stimulated by 

 pantothenic acid with this strain of yeast. However, pantoyltaurine in- 

 hibited the utilization of pantothenic acid in this and all other strains of 

 yeast. 



a,/?-Diaminopropionic acid is reported to have a marked growth-inhibit- 

 ing effect on Corynebacterium diphtheriae, both mitis and gravis strains, 

 presumably by competing with the essential growth factor, ^-alanine. 98 



a-Methyl-/?-alanine has been found to be slightly active in replacing 

 /^-alanine for the growth of Saccharomyces cerevisiae G. M. 74 



