A NOTE ON THE QUESTION OF THE IDENTITY 

 OF GASTRIC RENNIN AND PEPSIN. 



By EDWARD STAFFORD EDIE. 



Frofn the Physiology Department, Aberdeen University. 



{Received June 18th, 1921.) 



Much has been written on the question of the identity of gastric rennin and 

 pepsin, and two theories have been brought forward. One, first associated 

 with Pavlov [Pavlov and Parastschuk, 1904], is that pepsin and rennin are 

 identical, Savjalov [1905] and Gewin [1907] holding that coagulation is the 

 first stage in the digestion of milk by pepsin. The identity theory is based 

 on the parallelism between the behaviour of the proteolytic and milk coagu- 

 lating actions of gastric extracts under different conditions. The other theory 

 is that the enzymes are different. There are twt) possibihties here, one, put 

 forward by Nencki and Sieber [1901] and others, being that "pepsin" consists 

 of a large molecule with different side chains, one set of which digests protein 

 in acid solution, while another set is responsible for the coagulation of milk 

 in neutral solution. A second possibihty is that there are two distinct enzymes 

 involved in the two functions. This is the theory which has been mainly 

 developed by Hammarsten [1908]. It is difficult to distinguish experimentally 

 between these two possibihties, and indeed the present state of our knowledge 

 of the constitution of enzymes renders a distinction hardly practicable. Both 

 depend on the fact that by suitable treatment the two actions can be separated 

 from one another, so that a solution may be obtained which coagulates milk 

 but has no proteolytic action, and on the other hand it is also possible to 

 obtain an active proteolytic solution which has no milk coagulating pro- 

 perties. 



Porter [1911] in support of Hammarsten's theory found that various com- 

 mercial preparations, while coagulating milk, were actually anti-peptic. A 

 full discussion of the subject is given by Oppenheimer [1913]. 



When investigating the development of enzymes from foetal hfe onwards 

 I tested the properties of extracts of stomachs of young rabbits and compared 

 these with similar extracts from adult animals. The differences found are 

 recorded in this note. 



According to Oppenheimer, pepsin is already present in the stomach of 

 rabbits before birth, while according to Gmelin [1902] rennin is absent from 

 the stomach of new-born animals. Other observers find that rennin develops 



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