VELOCITY OF REACTION 69 



retarding action of the products of reaction is due almost entirely 

 to the fructose and not to the glucose, a result of great interest 

 in view of E. Fischer's discovery that it is only those disaccharides 

 which yield fructose on hydrolysis which are acted upon by in- 

 vertase, and showing that it is the fructose to which the enzyme is 

 adapted, probably by possessing such a chemical constitution that 

 it forms an unstable, incomplete, equilibrium compound with 

 that particular hexose. 



Henri further examined the action of emulsin upon salicin, 

 and here found, contrary to the preceding case, that the velocity 

 of reaction was less than that indicated by the logarithmic law ; 

 while in the case of the action of amylase upon starch, which he 

 also tested, he found that the law was closely obeyed. 



In addition to the empirical formula given above, Henri has 

 also deduced a somewhat complicated equation on a theoretical 

 basis, which yields for all the three enzymes worked with a fairly 

 close concordance with the experimental results obtained. 



Henri supposes that the enzyme is in part free, in part combined 

 with the hydrolyte or substratum, and in part combined with one of 

 the products of reaction. Further, that the latter portions in 

 combination, are unstable and determined by the usual equations 

 of equilibrium. 



Utilising these equations, and on the supposition that either the 

 free ferment or the portion combined with the cane-sugar is respon- 

 sible for the reaction, the following expression can be deduced for 

 the velocity of reaction 



dx K (a - x) 



dt ~ 1 + m (a - x) + n x 



in which m and n are the two equilibrium constants of the two 

 compounds of the ferment with the cane-sugar and fructose re- 

 spectively. 



This equation on integration yields 



K" a r/ \ * i a n * i a ~\ 



* I (m- n) - +n los + - log 



[_ 'a a-xj t 6 a-x_\ 



From his experimental data Henri deduced the values m = 30, 

 n = 20. In the case of emulsin acting upon salicin, where the 

 velocity of reaction is less than that demanded by the simple loga- 

 rithmic formula and continuously decreases as the reaction advances, 



