ENZYMES INVOLVED IN ALCOHOLIC FERMENTATION 331 



of two molecules of phosphorylated triose. Phosphotriose is further 

 phosphorylated to the diphosphorylated form and oxidized to diphos- 

 phoglycerate with the concomitant reduction of DPN to Ho-DPN. 

 The diphosphoglycerate after dephosphorylation and dehydration is 

 converted to phosphopyruvate. After dephosphorylation pyruvic 

 acid is decarboxylated to acetaldehyde and carbon dioxide. Acetal- 

 dehyde is reduced to ethyl alcohol with the concomitant oxidation 

 of Ho-DPN to DPN. 



Thus are thought to be formed the two main end products of alco- 

 holic fermentation, ethyl alcohol from the reduction of acetaldehyde 

 and carbon dioxide from the decarboxylation of pyruvate. Evidence 

 for the above-described transformations are by no means conclusive 

 in every instance. However, our state of knowledge concerning the 

 alcoholic fermentation is more advanced than for any other fermenta- 

 tion. For further detailed information see an excellent review by 

 Werkman and Wood ^° or Bacterial Chemistry and Physiology by 

 Porter.^^ 



Enzymes Involved in Alcoholic Fermentation. Traube's proposal 

 that fermentations are due to substances secreted by living cells was 

 borne out by the experiments of Buchner. It has been pointed out 

 that zymase has proved to be a battery of enzymes and coenzymes. 

 The reactions the individual enzymes catalyze have been described 

 above. 



The chemical natures of some of the enzymes involved in the 

 breakdown of sugar have been partially determined. Most of them 

 have been shown to be proteins in close association with specific 

 metals, such as magnesium, with the addition in some instances of 

 adenylic acid or its di- or triphosphate derivatives. 



The prosthetic group of diphosphoglyceraldehyde dehydrogenase, 

 DPN or Coenzyme I (the dialyzable, thermostable coenzyme or 

 cozymase of Harden and Young) ,, has been shown by von Euler, 

 Albers, and Schlenk ^^ to be a dinucleotide made up of adenine, nico- 

 tinic acid amide, two molecules of phosphoric acid and two molecules 

 of c?-ribose. The manner in which it oxidizes diphosphoglyceralde- 

 hyde and is itself reduced to the dihydro form is as follows. 



