370 ENZYMES 



an accelerating factor, for if the rate of fermentation of glucose 

 or of mannose by yeast-extract is greatly lowered by the 

 presence of a large excess of phosphate, the addition of a 

 relatively small quantity of fructose brings about a marked 

 acceleration in the fermentation. This is not due solely to the 

 fermentation of the added fructose, for the amount of carbon 

 dioxide evolved is much too great. This appears to be a 

 specific property of fructose, for the phenomenon does 

 not obtain when glucose is added to mannose or fructose, or 

 by mannose when added to glucose or fructose under the 

 proper conditions of concentration of phosphate in each case. 



Commenting on this. Harden and Young observe that " this 

 remarkable property of fructose, taken in connexion with 

 the facts that this sugar in the presence of phosphate is much 

 more rapidly fermented than glucose or mannose, and that 

 the optimum concentration of phosphate for fructose is much 

 higher than for glucose or mannose, appears to indicate that 

 fructose when added to yeast-juice does not merely act as a 

 substance to be fermented, but, in addition, bears some specific 

 relation to the fermenting complex ". 



It is supposed that fructose forms a permanent part of the 

 fermenting complex, so that a greater concentration of this 

 sugar in yeast-extract leads to the formation of an increased 

 quantity of complex. Thus, owing to the increased concen- 

 tration of this active catalyst, the yeast-juice could bring about 

 the reaction with sugar in the presence of phosphate at a 

 higher rate and, at the same time, the optimum concentration 

 of phosphate would become greater. 



Harden and Young also find that the addition of a 

 suitable amount of arsenate to a fermenting mixture of yeast- 

 extract and sugar (glucose, fructose or mannose) causes a 

 marked acceleration in the rate of production of alcohol and 

 carbon dioxide, which is continued long after a chemical 

 equivalent of carbon dioxide has been evolved. In this, the 

 action of arsenate differs from that of phosphate and, further, the 

 arsenate occurs in the free state throughout the period of fer- 

 mentation. This increased rate of fermentation is due to the 

 accelerating influence of the arsenate on the hexose-phospha- 

 tase ; the arsenate, however, cannot replace phosphate in the 

 fundamental reactions of alcoholic fermentation. 



