BUTYRIC ACI D-BUTANOL FERMENTATIONS 43 



carboxylic acids in addition to acetate and propionate, 

 namely formate, n-butyrate, rc-valerate, rc-caproate, lactate, 

 and vinylacetate. These include all the compounds that 

 are formed or readily metabolized by CI. kluyveri extracts. 

 In contrast, crotonate, /3-hydroxybutyrate, and acetoacetate, 

 which are relatively unreactive in the CI. kluyveri system, 

 do not serve as substrates for coenzyme A-transphorase. 

 This indicates that only those acids which can be converted 

 to their coenzyme A derivatives are highly reactive in this 

 system. 



Further evidence for the participation of the coenzyme A 

 derivatives of the four carbon acids in the metabolism of 

 CI. kluyveri has been obtained by studying the oxidation 

 of butyrate and the reduction of vinylacetate. Crude ex- 

 tracts of CI. kluyveri readily oxidize butyrate. However, 

 Stadtman 21 found that after these extracts were dialyzed 

 to remove soluble cofactors, butyrate was not oxidized unless 

 catalytic amounts of acetyl phosphate, a source of coenzyme 

 A, and other cofactors were added. This suggested that 

 butyrate had to be activated by conversion to either butyryl- 

 SCoA or butyryl phosphate before it was susceptible to 

 oxidation. Butyryl phosphate was excluded as an inter- 

 mediate by the observation that it was oxidized more slowly 

 than butyrate. Finally Stadtman 36 prepared butyryl-SCoA 

 and showed that it was oxidized rapidly in the absence of 

 free coenzyme A to acetoacetyl-SCoA, and in the presence 

 of coenzyme A to acetyl-SCoA. 



The evidence regarding the role of coenzyme A in the 

 reduction of vinylacetate to butyrate is similar though less 

 extensive. Peel 37 has found that a catalytic amount of 

 either acetyl phosphate or acetyl-SCoA is essential for vinyl- 

 acetate reduction. This points to the participation in this 

 reaction of vinylacetyl-SCoA which is known to be formed 

 from acetyl-SCoA and vinylacetate in the SCoA-transphorase 



