ALCOHOLIC FERMENTATION 265 



If the enzyme phosphatase, which hydrolyses the 

 hexose phosphate esters, is added, an increase in the rate 

 of fermentation will occur, due to the increased rate at 

 which the esters are hydrolysed and inorganic phosphate 

 set free to esterify more sugar. The same effect can be 

 brought about by the addition of arsenate, which stimu- 

 lates phosphatase activity (curve (3), Fig. 7). If the 

 phosphatase is sufficiently active to hydrolyse the esters 

 as fast as they are formed, a rapid fermentation un- 

 accompanied by any accumulation of ester will ensue. 

 The rate of fermentation is about the same as the 

 maximum obtained on addition of inorganic phosphate 

 (curve (2) ), but remaiixs constantly high as long as sugar 

 is available, since in effect the addition of phosphatase 

 (or its stimulation) is the same as a continuous addition 

 of inorganic phosphate. 



To account for these facts Harden and Young suggested 

 that sugar was fermented in two stages according to the 

 equations : — 



(1) iK'eHiaOe +2Na2HP04 >CeHio04(Xa2P04)2 + 2H2O +2CO2 +2C2H5OH. 



(2) C6Hio04(Na2P04)2 + 2H20 > (:,U,,(\+2:^a,KF0,. 



According to this scheme the first stage consists in the 

 esterification of one molecule of glucose to hexose di- 

 phosphate at the same time as a second molecule is 

 broken down to carbon dioxide and alcohol. The second 

 stage is the hydrolysis of the hexose diphosphate to sugar 

 and inorganic phosphate, which then go through the cycle 

 again, with fermentation of half the sugar at each cycle, 

 until it has all been converted into the end products. 

 The equation (1) represents the state of affairs occurring 

 when inorganic phosphate is added to the system (curve 

 (2)); equation (2) corresponds to the normal rate of 

 fermentation (curve (1) ). The addition of arsenate 

 causes tlie liydi'olysis of the esters acconlinu' to e(|uation 



