382 ENZYMES 



That phosphate is a necessity for alcoholic fermentation by 

 zymase is generally agreed, but views other than the above 

 have been put forward regarding the part played by it in 

 fermentation. 



Iwanoff,* for instance, considers that the phosphate formed 

 is a triose phosphate, the formation of which is not necessarily 

 accompanied by the evolution of carbon dioxide and alcohol, 

 since the combination will take place when a phosphate is added 

 to the filtrate of a solution of sugar which has been fermented 

 by yeast-extract. He also found that the sugar obtained from 

 the sugar phosphate is not fermented by living yeast. Iwanoff 

 concludes that there are three stages in alcoholic fermentation : 

 the sugar is first broken down into simpler sugars, then by 

 the action of an enzyme, termed synthease, a triose phosphate 

 is organized, which is then acted upon by alco.holase to form 

 carbon dioxide, etc. 



These views are not agreed with by Harden and Young, -f 

 who criticize the methods employed by Iwanoff. 



In addition to phosphate, other substances may act as co- 

 enzymes : thus Neuberg { finds that aldehydes generally ac- 

 celerate the alcoholic fermentation of dextrose and mannose, 

 and that a mixture of keto acids with potassium phosphate 

 acts as a coenzyme. 



The equations given above for the formation of hexose 

 phosphate, whilst representing an important preliminary re- 

 action, do not throw any light on the subsequent changes in- 

 volved in the formation of the alcohol, carbon dioxide, glycerol, 

 and acetic aldehyde from the sugar. Many theories have 

 been put forward to explain the mechanism of alcoholic fer- 

 mentation ; the more recent views of Neuberg and Reinfurth II 

 appear to be well supported by the facts of experiment. The 

 first action would appear to be a molecular rearrangement of 

 the glucose molecule with the formation of one molecule of 

 glyceric acid and one of dihydroxyacetone. 



* Iwanoff : " Centrlbl. Bakt.," 1909, 24, i 



f Harden and Young: id., 1910, 26, 178. 



J Neuberg : " Biochem. Zeitsch.," 1918, 88, 145. 



The amyl alcohol and succinic acid, which also are found amongst the pro- 

 ducts of alcoholic fermentation, are produced not from the sugar, but from the 

 protein present in the yeast cell (see p. 343). 



|| Neuberg and Reinfurth : " Ber. deut. chem. Gesells.," 1919, 52, B, 1677. 



