CHAPTER XI 

 INTESTINAL DIGESTION 



Strictly speaking, all digestive processes which take place in the 

 intestine may be classed under Intestinal Digestion. However, we will 

 consider under Intestinal Digestion only those digestive processes 

 which are brought about by enzymes which have their origin in the intes- 

 tine. The activities of those enzymes which originate in the pancreas 

 we have considered in Chapter X under Pancreatic Digestion. 



It has been shown 1 that the reaction of the small intestine may 

 vary from acid to alkaline and is influenced by the state of digestion. 



The enzymes of the intestinal juice (succus entericus) are of great 

 importance to the animal organism. These enzymes include erepsin, 

 sucrase, maltase, lactase, nucleases, and enterokinase. 



Erepsin is a proteolytic enzyme which has the property of acting 

 upon the proteoses, peptones, and pep tides which are formed through the 

 action of trypsin, and further splitting them into ammo-acids. Erepsin 

 has no power of digesting any native proteins except caseinogen, his- 

 tones, and protamines. It possesses its greatest activity in an alkaline 

 solution, although it is slightly active in acid solution. An extract of the 

 intestinal erepsin may be prepared by treating the finely divided intes- 

 tine of a cat, dog, or pig with toluene or chloroform- water and per- 

 mitting the mixture to stand with occasional shaking for 24-72 hours. 

 Enzymes similar to erepsin occur in various tissues of the organism. 



In cases of gastric cancer a pep tide-splitting enzyme is claimed to 

 be present in the stomach contents. The glycyl-tryptophane test is 

 sometimes used for its detection. Some investigators claim that the 

 peptide-splitting power of gastric juice in cancer is generally due to the 

 regurgitation of trypsin or erepsin from the intestine or to the presence 

 in the gastric contents of swallowed saliva which possesses peptolytic 

 power. The peptide-splitting power of saliva may be due to a specific 

 enzyme or to the presence of bacteria (see Glycyl-tryptophane Reaction, 

 page 202). 



The three invertases sucrase, maltase, and lactase are also important 

 enzymes of the intestinal mucosa. The sucrase acts upon sucrose 

 and inverts it with the formation of invert sugar (glucose and fructose). 

 Some investigators claim that sucrase is also present in saliva and 

 gastric juice. It probably does not exist normally in either of these 



l Long and Fenger: Jour. Am. Chem. Soc., 39, 1278, 1917. 



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