362 ENZYMES 



order, and as such is applicable to all cases of hydrolysis, as 

 for example : — 



Ci,H„,Oij + H2O = 2C6Hi,,06 



Although from the left-hand side of the equation it would 

 appear that two substances are reacting, the quantity of water 

 present is so large, as compared with the amount of cane 

 sugar, that its concentration is practically unaltered, and 

 therefore, for all intents and purposes, only a single substance 

 is undergoing alteration in concentration. 



Now the hydrolysis of cane sugar which takes place 

 slowly in aqueous solution is catalytically accelerated by the 

 addition of dilute mineral acids, the effect being greater in 

 proportion to the amount of acid used, without, however, 

 altering the order of the reaction ; in just the same way 

 enzymes accelerate hydrolyses in accordance with the law of 

 mass action for monomolecular reactions, thereby showing 

 that they are true catalysts. 



In reactions acting in accordance with the logarithmic 

 equation above given, the amount of substance changed in a 

 given time bears a constant ratio to, or is a constant fraction 

 of, the amount of substance unchanged ; on plotting the 

 amounts changed as ordinates against the time as abscissas 

 there is accordingly obtained what is known as a logarithmic 

 curve. 



Now it is found that when this is done for an enzyme re- 

 action the curve both at the beginning and at the end of a re- 

 action is not logarithmic but linear. Thus Horace Brown 

 and Glendinning* found that equal amounts of starch were 

 hydrolysed by diastase in equal times during the earlier part 

 of the reaction, in other words, the course of the reaction was 

 expressed by a straight line ; as the reaction proceeded, how- 

 ever, it became logarithmic, or, in other words, at the com- 

 mencement, when the concentration of the substance being 

 hydrolysed is great as compared with that of the enzyme, the 

 reaction is linear and not in accordance with the law of mass 

 action, but where the concentration of the enzyme is great as 

 compared with that of the substance being hydrolysed, the 

 reaction obeys the law of mass action. 



* Brown and Glendinning: "J. Chem. Soc, Lond.," 1902, 81, 392. 



