ENZYMES 191 



united residue and dialyzate, the mixture recovered its lypolytic 

 properties. A. HARDEN and W. J. YOUNG* made a similar observa- 

 tion when they ultrafiltered expressed yeast juice. The filter res- 

 idue lost its ability to cause fermentation but regained it when 

 mixed with the filtrate. It is evident from this, that some enzymes 

 consist of a colloid and a crystalloid constituent; the latter follow- 

 ing the suggestion of G. BERTRAND is called co-enzyme or co-ferment. 

 In still other ways the co-enzyme shows crystalloid properties; 

 unlike the colloid portion it is insensitive to boiling and frequently 

 consists of a substance whose composition is well known. Thus, 

 e.g., according to O. VON FURTH and J. SCHUTZ,* sodium cholate and 

 sodium glycocholate are co-enzymes of lipase; and according to 

 BIERRY and V. HENRI* the chlorin and bromin ions of alkaline salts 

 are the co-enzymes for the action of pancreatic juice upon starches. 



In contradistinction to the co-enzymes, the anti-enzymes are 

 usually colloids. Anti-enzymes are substances which interfere with 

 the action of enzymes. They are like the antitoxins which detoxi- 

 cate toxins, and like the antitoxins, they occur to some extent in 

 normal serum, or may be produced in it by the injection of enzymes. 

 For instance, horse serum contains a large amount of anti-rennin 

 which inhibits the coagulation of milk by rennin. By injecting the 

 proper enzyme, anti-enzymes for lipase, emulsin, amylase, pepsin, 

 papain and urease have been obtained. An exception to this is anti- 

 try psin which seems to be a crystalloid since it diffuses readily. It 

 is the anti-enzyme which protects intestinal parasites from digestion 

 by the pancreatic juices. 



According to S. G. HEDiN,* 2 the relationship between enzyme and 

 anti-enzyme is an adsorption, which probably results in a fixation. 



A certain similarity between enzyme and co-enzyme is possessed 

 by pro-enzyme and its activator. Most enzymes are formed in an 

 inactive state called the pro-enzyme, pro-ferment, or zymogen, which 

 becomes active only after the addition of some crystalloid, usually a 

 simple substance. The pro-enzyme of pepsin may be extracted from 

 the gastric mucous membrane, but cannot digest albumin; only after 

 the addition of very dilute acids does it become pepsin and acquire 

 its ability to digest. The trypsin of pancreatic juice is excreted into 

 the duodenum as an inactive pro-enzyme; it is activated by calcium 

 salts. This is of the greatest biological significance, since otherwise, 

 secreting glands would not be safe from their own secretions. 



According to E. PRIBRAM,* the formation of pro-enzymes occurs 

 in this manner; the protoplasm of the glandular cells retains a cer- 

 tain portion of the food by adsorption. Acids, calcium salts, etc., 

 arrest the adsorption, and the active ferment becomes free. In 



