42 BACTERIAL FERMENTATIONS 



butyric acid bacteria. It has already been mentioned that 

 Koepsell et al. 20 obtained evidence that extracts of CI. butyli- 

 cum catalyze the synthesis of butyryl phosphate from acetyl 

 phosphate and butyrate (reaction 7) . Clostridium kluyveri 

 extracts catalyze a similar reaction in which the phosphoryl 

 group is transferred from acetyl phosphate to other fatty 

 acids containing from three to eight carbon atoms. 34 In a 

 further study of this reaction using acetyl phosphate and 

 propionate, Stadtman 35 established that it is completely 

 dependent upon the presence of coenzyme A and phos- 

 photransacetylase. These requirements suggested that the 

 apparently simple phosphoryl transfer (reaction 22) actu- 

 ally involves three distinct enzymatic steps shown in the 

 following equations: 



Acetyl phosphate + HSCoA ^^ 



Acetyl-SCoA + Phosphate (19) 



Acetyl-SCoA + Propionate ^=^ 



Acetate + Propionyl-SCoA (20) 



Propionyl-SCoA + Phosphate ^±= 



Propionyl phosphate + HSCoA (2 1 ) 



Acetyl phosphate + Propionate ^=^ 



Acetate + Propionyl phosphate (22) 



Reaction 19 is the usual phosphotransacetylase reaction, 

 and reaction 21 is the analogous reaction involving pro- 

 pionyl phosphate, catalyzed by the same enzyme. Reaction 

 20 represents a reversible transfer of the SCoA group from 

 acetate to propionate. This transfer results in the acti- 

 vation of propionate and the deactivation of acetate. The 

 enzyme catalyzing this reaction has been partially purified 

 and named coenzyme A-transphorase. In the presence of 

 this enzyme the SCoA group may be transferred to several 



