406 CHEMICAL DYNAMICS 



The task of seeking for such a relation, when we recall all of the 

 factors which may very possibly enter into it, might well seem, 

 for purposes of practical utility, well-nigh hopeless, were it not 

 for the fact that the limiting cases of this general law have 

 already been ascertained to hold good over quite extensive and 

 practically attainable ranges of time and concentration. Evi- 

 dently the number of the factors which play an appreciable part 

 in determining the phenomena observed is not so great as we 

 might be inclined to anticipate. 



We have seen that Henri's law does not suffice; it is not 

 sufficiently general to cover all of the time- and mass-relations 

 in the hydrolysis of the polypeptids (Cf. the previous chapter, 

 section 2) ; we are led to suspect that some important factor has 

 been omitted in the derivation of Henri's equation. 



In the following chapter we shall see that pepsin is capable 

 of exerting synthetic activity under conditions such that its 

 hydrolytic activity is absent. We have already had occasion 

 to indicate that the proteolytic ferments may exist in more than 

 one modification. In the light of these facts we shall make the 

 following assumptions regarding the mode of action of the pro- 

 teolytic ferments upon the proteins. 



Let us suppose that the proteolytic ferments act as " carriers" 

 of water into the protein molecule, just as nitric oxide, in the 

 manufacture of sulphuric acid, acts as a " carrier" of oxygen into 

 sulphurous acid. We must therefore assume that these ferments 

 can exist both in a hydrated and in a dehydrated form, just as 

 nitric acid can exist in the reduced form of nitrous oxide. More- 

 over we must conclude that at the splitting of each COH.N 

 bond in the protein molecule some such reactions as the following 



occur : 



HF 

 I 



(A) -COH.N- + HFFOH = - COH.N - 



(hydrated I 



* FOH 



\ ferment-substrate compound) 



HF 



(B) - COH.N - - - COOH + H 2 N - + FF 



I (products of hydrolysis) (dehydrated 



FOH 



(ferment-substrate 

 compound) 



