PANTOTHENIC ACID 



that 25 in ratj on a diet low in caseinogen, administration of sulpha- 

 pyridine produced retardation of growth and other symptoms of panto- 

 thenic acid deficiency, which were relieved by giving pantothenic acid. 

 This result might, of course, have been due to an inhibitory effect of 

 sulphapyridine on the bacterial flora which under normal circumstances 

 may supply part of the normal pantothenic acid requirements of the 

 animal, but West et al.^^ suggested that sulphapyridine antagonised 

 pantothenic acid directly, making it unavailable, not only for the 

 host, thereby leading to the onset of symptoms of pantothenic acid 

 deficiency, but also for the invading bacteria. Sulphapyridine may 

 constitute a third method of blocking one of the routes by which 

 pantothenic acid is synthesised or utilised. 



Mechanism of the Inhibitory Action of Pantoyltaurine 



Haemolytic streptococci grown in presence of adequate amounts 

 of pantothenic acid exhibited a short lag phase, then a well-marked 

 logarithmic phase, during which growth rate was optimal and, finally, 

 a stationary phase which was reached in three to four hours. Reduc- 

 tion of the pantothenic acid concentration to sub-optimal levels had 

 little effect on the duration of the lag phase or on the rate of growth, 

 but reduced the stationary population. The addition of pantoyl- 

 taurine had quite a different effect. In presence of excess pantothenic 

 acid, pantoyltaurine had no effect on the stationary population, but 

 increased the lag period and reduced the rate of growth in the first 

 half of the logarithmic phase, though not to any considerable extent 

 the growth rate in the second half. Thus pantothenic acid appeared 

 to lead to the formation of substances necessary for normal growth, 

 and the action of pantoyltaurine was to reduce the formation of these 

 substances so that the rate of growth was limited. 2' Furthermore, 

 pantothenic acid was found to disappear from streptococcal cultures, 

 the disappearance being independent of the growth or viability of the 

 organism, but associated with glycolysis, for when glycolysis was 

 prevented, pantothenic acid metabolism ceased. Addition of pantoyl- 

 taurine, however, inhibited pantothenic acid metabolism without a 

 corresponding inhibition of glycolysis. These facts are understand- 

 able if it is assumed that both glycolysis and the presence of excess 

 pantothenic acid are necessary for the formation of a substance 

 essential for streptococcal growth, and that pantoyltaurine interfered 

 with the metabolism of pantothenic acid, but not with the energy- 

 yielding process of glycolysis.^* The nature of the substance formed 

 by pantothenic acid is discussed in a later section (page 390). 



Six other compounds (see page 398) which inhibited growth and 

 which, like pantoyltaiu"ine, were antagonised by pantothenic acid, 



384 



