ZYMASE 495 



a very different interpretation of the phenomenon. They 

 found that the addition of phosphate may increase the velocity 

 twenty-fold, but this increased rate falls off with time to its 

 original value ; the addition of a second quantity of phosphate 

 brings about a repetition of the phenomenon. Measurement 

 of the increased amount of carbon dioxide over that produced 

 in the absence of phosphate indicates that, within the limits 

 of experimental error, the increase in the amount of carbon 

 dioxide is equivalent to the amount of phosphate added, i.e. 

 R2H . PO4 = CO2, the amount of alcohol formed being in 

 proportion. 



If the solution is boiled directly the fermentation velocity 

 has fallen to its initial value, it is found that practically the 

 whole of the added phosphate is no longer precipitable by 

 uranium acetate, it is, in fact, in organic combination as a 

 hexose diphosphate, C6Hio04(R2P04)2. 



Fermentation by yeast-juice therefore takes place in 

 stages, the first of which is the formation of a hexose phos- 

 phate which takes place during the first period of temporary 

 acceleration : — 



(I) 2CeHi.Og + 2R2HPO4 = 2CO2 + 2C.,H,.0 + CeHioO.CPO^R,), + ^U.fi 



The above equation, however, may not be a complete 

 statement in view of the fact that the hexosediphosphate 

 is accompanied by a hexosemonophosphate. Thus Robison * 

 found that when fructose or glucose is fermented by yeast 

 juice, an hexosemonophosphate is formed together with the 

 hexosediphosphate. t In order to throw some light on this. 

 Harden and Henley J have redetermined the amounts of carbon 

 dioxide evolved and the hexosediphosphate and hexosemono- 

 phosphate produced. They find that the ratio of carbon 

 dioxide to total phosphorus esterified is on the average 

 0-9 ; it is invariably below unity, which indicates that some 

 esterification of phosphorus, about 10 per cent, takes place 

 without the evolution of carbon dioxide. The product of 



* Robison : " Biochem. Journ.," 1922, 16, 809. 



f A third hexosemonophosphate was prepared by Neuberg (" Biochem. 

 Zeit.," igi8, 88, 432) by the hydrolysis of hexosediphosphoric acid. 

 I Harden and Henley : id., 1927, 21, 1216. 



