40 BACTERIAL FERMENTATIONS 



presence of coenzyme A, the phosphotransacetylase reaction 

 was formulated as follows: 



Acetyl phosphate + HSCoA ^=±: 



Acetyl-SCoA + Phosphate (15) 



This reaction accounts for the observed phosphate exchange. 

 Since arsenate and phosphate have similar properties the 

 reverse reaction in the presence of arsenate would be 

 expected to give acetyl arsenate. This hypothetical com- 

 pound, which has never been prepared or isolated, pre- 

 sumably hydrolyzes rapidly to acetate and arsenate and thus 

 accounts for the arsenolysis reaction. Further evidence for 

 the correctness of reaction 15 was provided by the use of 

 substrate amounts of coenzyme A and the identification of 

 the product with Lynen's acetyl coenzyme A. This was 

 done in part by showing that the product of reaction 15 

 could serve as an acetyl donor in the enzymatic acetylation 

 of sulfanilamide and in the condensation with oxaloacetate 

 to give citrate. 



The easy interconversion of acetyl phosphate and acetyl- 

 SCoA by phosphotransacetylase opened the question as to 

 which of these compounds is the immediate product of 

 ethanol and acetaldehyde oxidations. Burton and Stadt- 

 man 30 investigated these reactions and found that ethanol 

 oxidation involves two enzymes. Reaction 16 is catalyzed 



CH3CH2OH + DPN+ ^=± 



CH3CHO + DPNH + H+ (16) 



CH3CHO + HSCoA + DPN+ ^=±: 



CH3COSC0A + DPNH + H+ (17) 



by a DPN-specific alcohol dehydrogenase. The further 

 oxidation of the resulting acetaldehyde by acetaldehyde 

 dehydrogenase (reaction 17) is dependent upon DPN and 



