1 80 IMMUNO-CATALYSIS 



enterokinase activates crude chymotrypsinogen to chymotrypsin. In 

 contrast, crystalline trypsin fails to effect this activation. This failure 

 was attributed to the presence of a trypsin inhibitor in the crude 

 chymotrypsinogen which combines with trypsin and inhibits its ac- 

 tivating property. After one crystallization of the crude chymotryp- 

 sinogen, however, the inhibitor remains in the mother liquor; trypsin 

 then is capable of activating chymotrypsinogen to chymotrypsin. 



The crude chymotrypsinogen also contains trypsinogen, which, 

 acted upon in the same manner (removal of inhibitor) by entero- 

 kinase, is transformed into trypsin. A sufficient amount of active tryp- 

 sin thus formed is capable of overcoming the inhibitory action of the 

 solution, resulting in the activation of chymotrypsinogen. The same 

 result is obtained by adding enough trypsin even in the presence of 

 the inhibitor. 



Balls and Swenson (1934) and Balls (personal communication) 

 stated that the trypsin-inhibitor of egg white was incapable of inhibit- 

 ing the activity of papain. One positive effect on papain was attrib- 

 uted to something else, since the search for the same positive effect 

 with other papain preparations utterly failed. Ross and Tracy (1942) 

 have studied the effect of the inhibitor of egg white on the digestion of 

 casein by chymotrypsin. They observed only 15 to 20 per cent inhibi- 

 tion. However, if the inhibitor was first incubated with casein (at 

 37.5°C. for 40 minutes) before adding the enzyme, no inhibitory effect 

 was observed. 



The delayed action of trypsin on raw egg white described by Bayliss 

 could not be due to this inhibitor for the following reasons. The tryp- 

 sin used by him was capable of hydrolyzing heat denatured egg white. 

 Since the inhibitor as found by Balls and Swenson is resistant to heat, 

 it should be still present in the heat denatured egg white in an active 

 form and therefore inhibit the active trypsin. Since heat denatured 

 egg white exercised no inhibitory effect on trypsin, the delayed action 

 of trypsin on raw egg white must be due to some other factor. The 

 possible nature of this factor is discussed below. 



c. The Resistance of "Living" Protein to the Action of Proteolytic 

 Enzymes. It has been known for a long time that all living cells are 

 resistant to proteolytic enzymes. Dead organisims are rapidly digested 

 by them. Several hypotheses have been advanced to explain this fact. 



