KINETICS OF HYDROLYSIS 



383 



equation expressing the course of hydrolysis is in reality equation 

 (i), but that as hydrolysis proceeds the reaction is subject to an 

 acceleration, possibly attributable, either directly or indirectly, 

 to the products of the reaction. 



Euler (9) has studied the hydrolysis of glycin by erepsin, 

 obtained from the intestinal wall. The method employed was 

 that of following the hydrolysis by measuring the progressive 

 alteration of the electrical conductivity of the solution, direct 

 proportionality between the alteration in conductivity and that 

 of the dipeptid-concentration having previously been established. 

 He finds that the velocity of hydrolysis is very intimately de- 

 pendent upon the alkalinity of the solution, thus: 



1/10 N GLYCYL-GLYCIN. 5 G. EREPSIN [POWDER IN 100 CC. 



Alkali-concentration N 0.04 0.05 0.075 0.10 



Reaction-velocity constant X 1000 0.05 7.0 6.2 2.6 0.2 



For a given initial NaOH, dipeptid and erepsin concentration 

 the monomolecular formula represents the progress of this re- 

 action with tolerable fidelity, as the following results show: 



0.10 N GLYCYL GLYCIN. 5 GRAMS EREPSIN IN 100 CC. 



0.04 AT Na 



0.05 N Na 



Within certain limits the reaction-velocity is independent of 

 the initial concentration of this dipeptid, but this holds good 

 only within certain limits of the proportion enzyme : substrate. 

 If the enzyme-concentration is small, for a given Na-concentra- 

 tion the reaction-velocity rises with increasing concentration of 

 glycyl-glycin. Euler attributes this fact to neutralization of 

 injurious excess of NaOH by the additional glycyl-glycin. The 

 progressive change in the reaction-constant as hydrolysis proceeds 

 may doubtless be attributed to the fact that the substrate and 

 products are possessed of different combining capacities for bases, 

 so that the proportion of free base alters as the reaction proceeds. 



