X, A, 1 Pratt: Papain 29 



The digestions at 70° show that the activity in the presence of 

 large amounts of enzyme is not greatly weakened, but with de- 

 creasing percentages of gum the loss becomes more marked. The 

 data covering the digestions at various temperatures are plotted 

 in fig. 4. This resistance to heat is rather unusual for an enzyme, 

 but has been commented upon by various investigators of papain. 

 Delezenne, Mouton, and Pozerski * note the rapid action upon egg 

 white and serum at temperatures of 80° and 90°. Chittenden'' 

 found that papain in acid solution digests more meat protein at 

 70° than at lower temperatures. However, I have found that a 

 papain solution rapidly heated to 100°, allowed to boil five 

 seconds, and immediately cooled with ice no longer shows any 

 proteolji;ic activity. 



STANDARD EVALUATION OF PAPAIN 



An examination of the curves in fig. 1 shows that the per- 

 centage of protein digested in thirty minutes increases rapidly 

 with small increments of enzyme in the first portion of the 

 curve. The range between 0.0 and 10 milligrams of papain 

 closely approximates a straight line, especially with ordinary 

 samples of gum, while the ratio of papain to protein digested 

 falls off more or less rapidly beyond this point, depending 

 upon the activity of the enzyme. The percentage of protein 

 digested by amounts smaller than 10 milligrams of low-grade 

 papain is so slight that this weight of gum has been decided 

 upon as the best for routine analyses. It is suggested that the 

 average of 6 determinations carried out in the manner pre- 

 viously described under "methods of analysis," using 25 cubic 

 centimeters of milk, 23 cubic centimeters of distilled water, 

 and 2 cubic centimeters of a filtered solution representing 10 

 milligrams of papain digested for thirty minutes at 40°, be 

 accepted as the standard and that the proteolytic activity of 

 the gum be designated by the ratio so obtained of 1 part of 

 papain to the digested protein. This may be called the activity 

 number of the sample. 



Table XXVIII shows the activity upon this basis of the 

 different samples of papain mentioned in this paper. 



' Compt. rend. Soc. biol. (1906), 60, 68 and 309; Pozerski, Ann. Inst. 

 Pasteur (1909), 23, 205 and 321. 



'Trans. Conn. Acad. Arts & Set. (1892), 9, 311. 



