NUTRITION OF MICRO-ORGANISMS 



of pyridoxine caused a still further increase in the number of oocysts 

 excreted.^' 



Biosynthesis of Pantothenic Acid 



Both halves of the pantothenic acid molecule function as growth 

 factors, jS-alanine for some strains of Cory neb aderium diphtheriae * and 

 pantoic acid for Acetobacter suboxydans ^^ and Clostridium septicum}^ 

 These organisms synthesise pantothenic acid by coupling ^-alanine with 

 pantoic acid, for the culture solution stimulated the growth of L. hel- 

 veticus which does not respond to either half of the molecule. ^^ Accord- 

 ing to T. Wieland and E. F. Moller,**^ yeast frozen in liquid air and 

 subjected to dialysis with aeration had a diminished capacity for 

 synthesising pantothenic acid from ^-alanine and pantolactone. The 

 ammonium ion and probably the carbonate and acetate ions activated 

 the synthesis and the ammonium ion also catalysed the synthesis of 

 pantothenic acid from ^-alanine and pantamide. 



From what has been said above, it is evident that many antagonists 

 of pantothenic acid owe their effect to interference with the synthesis 

 of pantothenic acid from pantoic acid and j8-alanine, although pantoyl- 

 taurine acts by interfering with the utilisation of pantothenic acid to 

 form substances essential for the growth of the bacterial cell. The 

 nature of the substance produced by the metabolism of pantothenic 

 acid is discussed below (page 390). 



Salicylic acid owes its antibacterial action to its ability to interfere 

 with the synthesis of pantoic acid,^^» ^^» ^^ whilst other antagonists, 

 for example a- and y-hydroxy-j8j8-dimethylbutyric acid and j3y-dir 

 hydroxy-^-methylbutyric acid, apparently prevent the coupling 

 of /3-alanine with pantoic acid.^® Another growth inhibitor, cysteic 

 acid, acts by interfering with the formation of j8-alanine by the 

 decarboxylation of aspartic acid.*^ In E. coli, pantothenic acid 

 and j8-alanine completely prevented the toxic effects of cysteic acid, 

 and the rate of synthesis of pantothenic acid was determined by the 

 ratio of cysteic acid to aspartic acid. Glutamic acid was three times 

 as effective as aspartic acid in preventing the toxic effects of cysteic 

 acid, owing to its conversion by transamination into a-ketoglutaric 

 acid, which had a " sparing action " on pantothenic acid, that is, it 

 permitted the cells to grow at a lower rate of pantothenic acid synthesis ; 

 citric acid and cts-aconitic acid had a similar effect, but oxaloacetic 

 and pyruvic acid, the precursors of czs-aconitic acid, were inactive.'*^ 

 Glutaric acid also enhanced the growth of S. cerevisiae and S. carls- 

 bergensis in presence of suboptimal amounts of pantothenic acid ; 

 the " sparing action " in this instance is attributed to the combination 

 of glutaric acid with pantothenic acid or j3-alanine to give a substance 

 which had greater growth-promoting activity. ^^ 



387 



