94 TISSUE FERMENTS 



Inhibition of Proteolytic Processes by the Products of 

 Protein Cleavage. It has long been known that the action 

 of proteolytic ferments is inhibited by the presence of pro- 

 tein cleavage products. It has been repeatedly shown that 

 the inhibitive influence is due to the optically active amino- 

 acids, in which this power resides, which exist in the proteins. 

 It is suggested in explanation that these aminoacids (and 

 only these) bind the ferment and thus prevent its fixing its 

 object of prey, the protein molecule. This is merely sug- 

 gested because the test tube is incapable of affording a true 

 picture of the proteolytic processes which are going on in 

 the living body. It should be realized that in the living body, 

 whether proteolysis is taking place in the digestive canal or 

 in the tissues, the cleavage products of protein are removed, 

 as they are formed, from further contact with the proteolytic 

 enzyme, and thus the inhibition inevitable in the test tube is 

 avoided. 



Moreover a natural prolongation of proteolytic cleavage 

 may be conceived from the fact that ceteris paribus the 

 longer molecular chains are more readily preyed upon than 

 short ones; with equal amounts of ferment and equal 

 molecular concentration of polypeptids, a tetrapeptid is split 

 more quickly than a tripeptid, and the latter in turn more 

 quickly than a dipeptid. 



Classification of Proteolytic Ferments. By substitu- 

 tion of definite polypeptids for high-molecular proteins a 

 basis will be found for construction of a rational classi- 

 fication and differentiation of proteolytic ferments. We 

 know today, for example, that pepsin is incapable of 

 acting upon any of the hitherto demonstrated polypeptids ; 

 that trypsin will separate some of them but by no means 

 all; while erepsin can dissociate even those polypeptids 

 which, like glycylglycin, successfully resist trypsin. Keep 

 in mind that every cell and every cellular combination 

 in animals and plants, from infusorium and bacterium up to 



