COENZYMES DERIVED FROM B VITAMINS 



163 



acid-carbonyl addition product with the keto acid before the cleavage of 

 the carbon-to-carbon bond, 143 as indicated below: 



O 



H 1 



HC— C=0 + 

 H 



pyruvic 

 acid 



H O 

 O— P— OH 



O 



C— OH 



H 1 

 HC— C- 



)— OH 



0— P- 



P— OH 



OH 



keto acid 

 addition 

 product 



H 

 HC— C=0 



O 



h4 



—OH 



O— P— OH 



Ah 



acetyl 

 phosphate 



formic 

 acid 



The acid-keto addition product of this earlier hypothesis could very well 

 be an intermediate in the mechanisms recently postulated. 



The "phosphoryl-aeetyl intermediate," if not used immediately for 

 acetylation, probably reacts with adenosine diphosphate, producing 

 adenosine triphosphate and acetic acid. In this way most of the energy 

 resulting from the degradation of pyruvic acid to acetic acid is conserved 

 in the formation of a high-energy pyrophosphate bond which can be 

 used by the cell for subsequent energy-requiring processes. The reactions 

 for the overall process can be summed up in this equation : 



Pyruvic acid +H3PO4+ adenosine diphosphate — >• 



acetic acid + formic acid +adenosine triphosphate 



Attempts to demonstrate the reversibility of this process led to the 

 experiments which clarified the nature of the acetyl derivative. Synthetic 

 acetyl phosphate, when added to formic acid in the presence of the enzyme 

 system, did not yield measurable amounts of pyruvic acid, but biological 

 preparations of the phosphoryl-aeetyl intermediate (prepared by an 

 enzymatic synthesis from acetic acid and adenosine triphosphate) were 

 found to be almost quantitatively converted to pyruvic acid when an 

 excess of formic acid was used. 142a 



(4) Production of Molecular Hydrogen by a Phosphoroclastic Splitting 

 of Pyruvic Acid. Clostridium butylicum possesses an enzyme which car- 

 ries out a reaction similar to the one just discussed, except that the avail- 

 able hydrogen atoms are disposed of as molecular hydrogen instead of 

 combining with the elements of carbon dioxide to form formic acid. 

 Acetic acid was first thought to be a primary product of the reaction, 144 

 but when phosphate was found to be an essential part of the system it was 

 postulated, on the basis of substantial evidence, that acetyl phosphate 

 rather than acetic acid was first formed, and that the acetic acid was a 



