ACETIC ACID FORMATION 151 



of the organism, the transfer of the hydrogen being catalysed 

 by diaphorase (see substrate Type S3, Table III). 



Diaphorase 



Reduced coenzyme I + Cytochrome > Coenzyme 



-f- Reduced cytochrome (3) 



and the final link with atmospheric oxygen is made by cyto- 

 chrome oxidase catalysing the transfer of hydrogen from 

 reduced cytochrome to combine with atmospheric oxygen, 

 forming water. The complete series of reactions have the 

 over-all results of Reaction I. Acetaldehyde is further 

 oxidised, presumably to acetic acid in the first place, although 

 this does not seem to have been proved : 



CH3.CHO + O ^CHg.COOH (4) 



Mammalian tissues carry out a similar oxidation through 

 the action of aldehyde oxidase which is a flavoprotein and 

 catalyses the oxidation of its substrates by atmospheric 

 oxygen without the intermediary action of other carriers 

 (substrate Type S^, Table III). The oxidation has not been 

 studied in detail in Esch. coli. Acetic acid is also formed from 

 pyruvic acid and the enzyme concerned, pyruvic oxidase, has 

 been studied in extracts of L. delbreucHi. If the enzyme 

 preparation is purified and dialysed, it will attack pyruvic acid 

 only in the presence of thiamindiphosphate and inorganic 

 phosphate, and the products of the reaction are acetyl phos- 

 phate and carbon dioxide: 



+ CH3 . CO . COOH + HgPO^^ 



CH3.COOPO3H2 + CO2 + H2O (5) 



If adenosine-di-phosphate (ADP) is added as phosphate- 

 acceptor, then the acetyl phosphate gives up its phosphate to 

 form adenosine-tri-phosphate and acetic acid: 



CH3 . COOPO3H2 + ADP = €H3 . COOH + ATP .... (6) 



The over-all reaction therefore involves an oxidation of 

 pyruvic acid to acetic acid and the synthesis of ATP from 

 inorganic phosphate. This reaction is therefore called an 



