CH. VIII.] TRYPSIN. 211 



body in small amounts. It converts trypsinogen to 

 trypsin, but the mechanism of this change is not fully 

 understood. From the fact that a small amount of the 

 kinase can in time activate a large amount of trypsinogen 

 it is probable that the process is enzymatic, and not merely 

 the union of two substances, each of which alone is in- 

 active. It is remarkable that the rate of activation is at 

 first slow, but increases very rapidly as the process nears 

 completion. This is opposed to the rate of action of other 

 enzymes which is most rapid at the commencement, and 

 which falls off as the concentration of the substrate 

 decreases. No satisfactory explanation of this so-called 

 "autocatalysis" has been offered. Enterokinase acts best 

 in a faintly acid medium, but the optimum P H has not been 

 studied. Since the contents of the small intestine are still 

 acid when the pancreatic juice is secreted, it is possible 

 that the conditions of the medium are such as will enable 

 the enterokinase to rapidly activate the trypsinogen. 



Trypsin acts best in a slightly alkaline medium, the 

 optimum PH being about 8-1. In the absence of proteins, 

 which exert a protective action, it is slowly destroyed by 

 alkalies at body temperature. At room temperature, 

 according to the author's observations, it is most stable at 

 about P H = 5-5. It is not readily destroyed in solutions as 

 acid as P H = i *5, though at such a reaction it does not act 

 as an enzyme. 



According to the observations of J. Mellanby and 

 Wooley, trypsin is more stable in acid solution than when 

 neutral or alkaline. They claim that in the presence of a 

 small amount of free acid trypsin can be heated to 100 C. 

 for 5 minutes without being completely destroyed, whereas 

 in slightly alkaline solution it is completely destroyed at 

 60 C. They find that the chlorides of barium and calcium 

 are effective agents in preserving trypsin at body tempera- 

 ture. 



Trypsin acts on all soluble and on many insoluble 

 proteins. It finally converts them to a mixture of amino- 

 acids and of relatively simple polypeptides. The hydrolysis 



