TRYPTIC DIGESTION 37 



In one extreme case I examined a solution of trypsin which had been in 

 the laboratory for over ten years. It had no digestive action on fibrin at all, 

 but still digested caseinogen to the extent of 26-6 cc. under the usual condi- 

 tions. 



These facts afford further evidence that the digestion of fibrin and of 

 caseinogen by pancreatic extracts is either due to different enzymes or at 

 least to different side chains if only one enzyme is involved. In my previous 

 paper [1914] I mentioned that the power to digest caseinogen seemed to be 

 less affected by heat than the power to coagulate milk, which was taken as 

 the measure of activity of trypsin by Mellanby and Woolley. I further sug- 

 gested that different sets of side chains might be responsible for these different 

 functions. 



In a later paper [1914] Mellanby and Woolley take exception to my sug- 

 gestion and say "Pancreatic rennin and trypsin are identical. In fact the 

 coagulation of milk by trypsin is an expression of a general law that all 

 proteolytic ferments coagulate milk provided sufficient calcium be contained 

 in it." These authors further say "The unique fact that the ferment or fer- 

 ments in pancreatic juice which digest protein and coagulate milk should 

 withstand boihng in acid solution is practically conclusive piX)of that the two 

 actions are produced by one and the same substance." If this assumption 

 of Mellanby and Woolley is correct, however, then the milk coagulating power 

 and the power to hydrolyse both fibrin and caseinogen should presumably 

 be quite parallel in their behaviour. The experiments detailed in the present 

 paper, and those described previously [Edie, 1919], however, tend to show 

 that the digestion of j&brin and of caseinogen, if carried out by one enzyme, 

 involves at least two sets of groups of the enzyme molecule, and therefore 

 cannot be said really to be produced by the same substance in the sense 

 evidently meant by Mellanby and Woolley. 



I have also carried out some experiments comparing the milk coagulating 

 power of pancreatic extracts with their proteolytic power, and shall now deal 

 with these. 



25. To 20 cc. of pancreatic extract (alcoholic) was added 0-5 cc. N HCl. Half of this was 

 then heated to 100° for 1 minute and filtered. 



1 g. fibrin. Digestion 2-75 hours at 37°. 



(a) 1 cc. trypsin, 40 cc. 0-5 % NagCOj. Digestion 21-0 cc. NjlO nitrogen. 

 (6) 1 cc. trypsin (heated), 40 cc. 0-5 % NagCOg. Digestion 10-2 cc. iV/10 nitrogen. 

 To 20 CO. milk was added 1 cc. of trypsin (1) fresh trypsin. 

 „ „ „ „ „ (2) heated trypsin. 



(1) Complete coagulation in 6 minutes at 37°. 



(2) No coagulation in 3 hours. 



26. (Similar to last experiment. 



1 g. fibrin. Digestion 2-5 hours. 



(a) 1 cc. trypsin, 40 cc. 0-5 % NagCOg. Digestion 26-2 cc. 

 (6) 1 cc. trypsin (heated), 40 cc. 0-5 % NajCOg. Digestion 8-1 cc. 

 ( 1 ) 20 cc. milk, 1 cc. fresh trypsin. Complete coagulation in 5 minutes, 

 ' (2) 20 cc. milk, 1 cc. heated trypsin. No coagulation in 2 hours. 



(503) 



