KINETICS OF PROTEIN HYDROLYSIS 405 



would appear that in these instances, at least, the extent of 

 hydrolysis after a given time must be proportional to the square 

 root of the ferment-concentration (41). 



The influence of the formation of compounds between the 

 substrate and the enzyme upon the kinetics of hydrolysis is very 

 clearly revealed by the experiments of Bogddndy (10) who has 

 shown that when a large excess of substrate is present the velocity 

 of protein hydrolysis by pepsin depends only upon the mass of 

 the ferment, while, when a large excess of ferment is present, 

 it depends only upon the mass of the substrate. This is obviously 

 what we should expect to be the case were the actual substance 

 undergoing hydrolysis a compound of the substrate and the 

 enzyme. 



The hydrolysis of caseinates by trypsin has been exhaustively 

 investigated by Walters (146) who has shown that the relation 

 between the time of hydrolysis and the amount of sodium casein- 

 ate hydrolysed is, for all stages of the reaction, almost exactly 

 what would be expected from the monomolecular formula. More- 

 over the velocity of hydrolysis is directly proportional to the 

 concentration of trypsin and there is a less exact proportionality 

 between the initial concentration of the substrate and the velocity 

 of hydrolysis, the velocity-constant decreasing slightly as the 

 concentration of the substrate increases. The nature of the 

 base combined with the casein has little or no influence upon 

 the process of hydrolysis by trypsin (although it has a decided 

 influence upon the velocity of autohydrolysis (147)) from which 

 we may infer, since caseinates of the alkalies and of the alkaline 

 earths are hydrolysed with equal velocity, that the degree of 

 electrolytic dissociation of the caseinate has little or no effect 

 upon the velocity of its hydrolysis by trypsin. 



We thus see that under different conditions of enzyme- and 

 substrate-concentration and with different substrates very dif- 

 ferent laws are found to express the relationship between time 

 and the extent of hydrolysis of the proteins and polypeptids. 

 None of these relations holds good outside certain definite limits 

 of substrate- and enzyme-concentration and each of them only 

 holds good for a limited portion of the hydrolysis. We are in- 

 clined to suspect that each of these relations is but part of some 

 more general relation which, it is possible, holds good for all 

 of the cases cited above and for all stages of the hydrolysis. 



