376 CHEMICAL DYNAMICS 



upon it greater susceptibility to pepsin than the shorter poly- 

 peptid chains possess. In support of the former view it is pointed 

 out that although erepsin, obtained from the succus entericus, 

 is able to hydrolyse peptones and polypeptids, yet it cannot 

 hydrolyse proteins, a fact which would appear to point towards 

 the existence of a few linkages in proteins which are not pres- 

 ent in polypeptids. In support of the latter view it is pointed 

 out that polypeptid-chains of greater length are more susceptible 

 to attack by other enzymes (i.e., trypsin) than the shorter chains, 

 so that the possibility cannot be overlooked that the suscepti- 

 bility of proteins to attack by pepsin may merely be attributable 

 to their great complexity, i.e., to the extreme length of the 

 polypeptid-chain. 



2. The Kinetics of the Hydrolysis of Polypeptids by Proteo- 

 lytic Enzymes. The progressive hydrolysis of diglycyl-tyrosin 

 in the presence of trypsin was followed by Taylor (19). He 

 states that the results which he obtained were irregular and un- 

 satisfactory, but he regarded these irregularities as being attrib- 

 utable to analytical errors. 



The optically active dipeptids, d-alanyl-d-alanin, d-alanyl- 

 1-leucin and glycyl-1-tyrosin, have been employed by Abderhalden 

 and Koelker, Abderhalden and Michaelis and Abderhalden and 

 Gigon (3) (4) (6) (14) in investigating the time relations of their 

 hydrolysis by trypsin. The degree of hydrolysis at any moment 

 can readily be followed by observing the optical rotation of the 

 solution, the rotation due to d-alanyl-d-alanin, for example, being 

 negative (a D 20 = 21.2), while that of the products of complete 

 hydrolysis is positive. The change in the optical rotation is, of 

 course, directly proportional to the degree of hydrolysis.* 



The relation between the time and the extent of hydrolysis 

 is, as Abderhalden and Michaelis have shown, susceptible of 

 fairly simple formulation. The form of relation which is char- 

 acteristic for a monomolecular reaction (that is, a transformation 

 which involves only one species of molecule) is expressed by the 

 differential equation: 



* Subject to a slight correction due to the fact that the specific rotatory 

 powers of the dipeptids are not absolutely independent of their concentrations. 

 Cf. Koelker (14). 



