680 PANTOTHENIC ACID 



arabinosus. Since coenzyme A is essential for acetylcholine formation, it 

 is readily seen why pantothenic acid-deficient cells of L. plantarum form 

 decreased amounts of this ester. Since oxidation of acetate (and hence of 

 pyruvate) in many organisms proceeds through the Krebs cycle, and since 

 coenzyme A is necessary for the initial formation of citric acid in this cycle, 

 the reason for the stimulation of oxidation of pyruvate by pantothenate in 

 deficient cells of Proteus becomes apparent. By way of contrast, the anaero- 

 bic fermentation of glucose by yeast juice was not decreased in pantothenic 

 acid deficiency.^®^ 



The extensive studies of Mcllwain on the mechanism of the inhibitory 

 action of pantoyltaurine for pantothenic acid-requiring bacteria may also 

 be explained on this basis. Mcllwain showed that addition of pantoyltau- 

 rine increased the lag phase and decreased the rate of growth during the 

 first half of the logarithmic phase of Streptococcus hemolyticus, observations 

 consistent with the assumption that pantoyltaurine slowed incorporation 

 of the vitamin into a substance necessary for normal growth.^^^ Pantothenic 

 acid disappeared from cultures of this organism; this disappearance was 

 dependent upon the simultaneous occurrence of glycolysis, but was pre- 

 vented by pantoyltaurine even though glycolysis was not. It may now be 

 assumed that the pantothenic acid was being converted to coenzyme A, an 

 endergonic process that was dependent upon giycolysis,^"^ and that this 

 conversion was the process inhibited by pantoyltaurine. Related antime- 

 tabolites of pantothenic acid probably inhibit growth by a similar mecha- 

 nism.^^" 



The observation that either pantothenic acid or tryptophan suffices to 

 permit growth of a strain of Staphylococcus aureus under specified condi- 

 tions'" indicates a relationship of the vitamin to metabolism of this amino 

 acid. The nature of this relationship has not been clarified. 



X. Pharmacology 



SAMUEL LEPKOVSKY 



Little is known concerning the pharmacology of pantothenic acid. Its 

 toxicity is very low and varies with different animals.^"* Acute toxicity was 



267 P. C. Teague and R. J. Williams, /. Gen. Physiol. 25, 777 (1942). 



268 H. Mcllwain, Biochem. J. 36, 364 (1942). 



269 H. Mcllwain and D. E. Hughes, Biochem. J. 38, 184 (1944). 



270 H. Mcllwain and D. E. Hughes, Biochem. J. 39, 133 (1945). 



271 M. G. Sevag and M. N. Green, /. Biol. Chem.. 154, 719 (1944); J. Bacteriol. 48, 631 

 (1944). 



1 K. Unna and J. G. Greslin, /. Pharmacol. Exptl. Therap. IZ, 85 (1941). 



I 



