414 CHEMICAL DYNAMICS 



activating trypsin is thus readily understood. When the con- 

 centration of unneutrahzed base is in excess of 10 X 10~^ all of 

 the trypsin is combined with the base and in the form of the 

 proteolytically active salt;* but when the alkalinity falls below 

 this limit a proportion of the trypsin is no longer combined with 

 alkali and this proportion is inactive. Below this limit of OH' 

 concentration, therefore, the velocity-constant of hydrolysis 

 (calculated from the monomolecular formula) must fall off in 

 proportion as Cqh' decreases, in other words, the relation be- 

 tween CoH' and time will be expressed by the bimolecular 

 formula. 



This explanation of our results is especially supported by the 

 fact that when the velocity of hydrolysis has fallen very low, 

 owing to decreasing alkalinity, the velocity can be raised again, 

 and the order of the reaction again made monomolecular, by 

 simply increasing the alkalinity of the solution. This is shown 

 in table III in which the break indicates that fresh alkali was 

 added. 



We may therefore conclude that in all probability pepsin and 

 trypsin are only able to exert their proteolytic activity (i.e., act 

 as carriers of water) when they are present in their solutions in 

 the form of salts with acids and bases respectively. 



The above experiments establish a lower limit of hydroxyl- 

 concentration, below which the alkalinity is not sufficient to 

 secure the greatest velocity of transformation. An upper limit, 

 above which the alkalinity is too great to secure the greatest 

 velocity of transformation, is indicated by the fact that trypsin 

 undergoes autohydrolysis in solution and this autohydrolysis is 

 greatly accelerated by alkalies (144) (145); directly, therefore, 

 the rate of destruction of the trypsin by the excess of alkali 

 measurably affects the progress of the reaction an upper limit 

 of alkalinity is reached. The experiments of Taylor, cited above, 



N N 



establish this upper limit at about ,, _„„ OH'; between ., ^.nn f^nn. 

 ly 1500 1,000,000 



and TTPTK OH', therefore, all alkalinities are equally favorable. 

 1500 



* Subject, of course, to dehydration as in equations (C) and (D) in the preced- 

 ing section. In equations (viii) and (ix) it is the value of F which is to be con- 

 sidered as being affected by the alkaU, not the proportion of the hydrated to 

 the dehydrated form of the enzyme, although this may also very possibly be 

 affected by the OH' concentration, j 



