524 DIGESTION 



and tissues. It has also recently been shown that the activity of trypsin 

 does not depend on the presence of free hydroxyl ions, but that it may 

 proceed in the presence of a decided amount of free acid. If pepsin 

 is present together with trypsin in a distinctly acid solution, the pep- 

 sin seems to destroy the trypsin, unless the mixture contains a con- 

 siderable ' quantity of protein, when the tryptic activity may persist 

 even for several hours. A practical conclusion that we may draw from 

 these results is to the effect that preparations of trypsin the so-called 

 pancreatin, for example if given with the food, may pass in an active 

 condition into the duodenum, where, in the more favorable environment 

 created by the neutralization of the excess of acid, it will develop its 

 proteolytic power. The therapeutic administration of pancreatin is, 

 therefore, justified (Long 24 ). 



The activated trypsin acts on proteins in very much the same way as 

 pepsin, except that the decomposition of the peptone and proteoses into 

 polypeptides is the chief feature of the process. Thus, after tryptic 

 digestion has proceeded for some time, only a trace of primary proteoses 

 but considerable quantities of leucine, tyrosine and other amino acids 

 will be found present. Some investigators believe that the thorough 

 nature of the digestive action of activated pancreatic juice may depend 

 on its also containing erepsin, an enzyme which we shall see to be pres- 

 ent in considerable amount in the mucous membrane of the intestine and 

 other tissues, and whose particular function is to split polypeptides into 

 the amino acids. From the autolytic digestion which takes place in 

 organs kept in a sterile condition after death, tryptic digestion differs 

 in that it produces only small quantities of ammonia. The large quanti- 

 ties of ammonia produced in autolytic digestion no doubt have a rela- 

 tionship to the acids simultaneously set free during this process. 



In the products of tryptic digestion it is usually found that, although 

 there has been considerable splitting of the protein into amino acids, 

 there are still a good many amino-carboxyl (NHCO) linkages left un- 

 broken, indicating that certain polypeptides are still intact in the mix- 

 ture. To split the polypeptides requires the aid of the erepsin, which is 

 present in the mucous, membrane of the intestine. Interesting inves- 

 tigations have been made on the exact degree to which trypsin-entero- 

 kinase can split up the various known polypeptides. This seems to 

 depend on the structure of the polypeptide molecule and on the number 

 of amino acids present in the chain. For example, alanylglycine, but 

 not glycylalanine is hydrolyzed, although both contain the same amino 

 acids but linked together in a different way; and tetraglycylglycine, 

 which contains five glycine radicles, is hydrolyzed, whereas diglycylgly- 

 cine, which contains only three, is not. 



