FERMENTS, OB ENZYMES 81 



sin, etc. are inoculated in animals, they cause specific antienzymes to 

 appear in the blood of the inoculated animal. Thus, when antirennin 

 serum is added to milk it greatly hinders clotting on the subsequent 

 addition of rennin. It is probable that powerful antienzymes are pro- 

 duced in the animal body for the purpose of protecting the tissues from 

 attack by enzymes. It is on account of the presence of antienzymes 

 that intestinal parasites can exist in the intestine, and the immunity 

 from digestion which the mucosa of the gastrointestinal tract enjoys, 

 is believed to be due to the same cause. But there is considerable doubt 

 regarding this claim. Fresh pancreatic juice when injected into the 

 empty intestine digests its walls. When food is present in the intes- 

 tine it evidently prevents digestion of the walls by diverting the enzyme 

 to itself. 



Types of Enzymes 



Having learned something about the general nature of enzyme action, 

 we may now turn our attention to certain details that have a practical 

 importance. In the first place, with regard to nomenclature, in the 

 earlier work each newly discovered enzyme received a name which was 

 often quite inappropriate. Many of these names are retained, such as 

 pepsin, trypsin, ptyalin, etc., but it is now customary to name the 

 enzyme according to the substance on which it acts. This is done either 

 by replacing the last part of the name of the substance acted on by the 

 termination -ase (for example, the enzyme which inverts maltose is called 

 maltase), or by merely adding -ase to the name of the substance acted 

 upon (thus, the enzyme which hydrolyzes glycogen is called glycogenase). 



Most of the enzymes in the animal body accelerate hydrolytic proc- 

 esses and are classified according to the chemical nature of the sub- 

 strate on which they work. Thus, we have: 



1. The amylases accelerating the hydrolysis of polysaccharides, e. g., 

 ptyalin (in saliva), amylopsin (in pancreatic juice), glycogenase (in 

 liver), diastase (in malt). 



2. The invertases accelerating hydrolysis of disaccharides, e. g., malt- 

 ase, lactase and sucrase (in succus entericus). 



3. The proteinases accelerating hydrolysis .of proteins, e. g., pepsin 

 (in gastric juice), trypsin (in pancreatic juice), erepsin, intracellular 

 proteinases. 



4. The Upases accelerating disruption of neutral fats, e. g., steapsin 

 (in 'pancreatic juice), intracellular lipases. 



5. Arginase accelerating hydrolysis of arginin into urea and or- 

 nithin, (intracellular). 



