HYDROLYSIS OF POLYPEPTIDS 375 



trypsin, are able to bring about the hydrolysis of leucyl-alanm. 

 The possibility was thus clearly indicated that a variety of enr 

 zymes might be found to exist in the various tissues and tissue 

 fluids, distinguishable from one another in then: power to hydro- 

 lyse various polypeptids, but only with difficulty distinguishable 

 from one another in their action upon proteins, since every pro- 

 tein, it might be anticipated, contains unions susceptible to attack 

 by any one of these enzymes. 



The possibility thus indicated has been rendered a certainty, 

 thanks to the extensive researches of Abderhalden and his col- 

 laborators (2). These investigators have employed the extracts 

 and press-juices of various organs, prepared by Buchner's method 

 of grinding up with sand and kieselguhr and pressing out at a 

 pressure of 100 to 300 atmospheres, which contain a number of 

 different enzymes capable of bringing about the hydrolysis of 

 various polypeptids. These enzymes are not so selective in their 

 action as pure trypsin, they can hydrolyse polypeptids which 

 trypsin cannot, and the press-juices of different organs exhibit 

 characteristic differences in regard to the polypeptids which 

 they can and those which they cannot attack. Most striking 

 differences were observed between the enzymatic activities of 

 the red blood-corpuscles and those of the plasma which bathes 

 them. The red corpuscles of the horse (but not those of the ox) 

 hydrolyse glycyl-1-tyrosin, which is not hydrolysed by white 

 corpuscles nor by plasma or serum; they also hydrolyse diglycyl- 

 glycin which, it will be recollected, is not hydrolysed by trypsin. 

 Plasma and serum both hydrolyse d-1-alanyl-glycin, diglycyl 

 glycin and triglycyl glycin; hence the enzymatic activity of the 

 serum is not attributable to trypsin or erepsin absorbed from 

 the intestinal wall. 



Pure pepsin, prepared by Pavlov, does not act upon any of 

 the polypeptids, whereas it splits the natural proteins into some 

 half-dozen peptones and proteoses, although it does not split 

 these substances (which are in reality polypeptids) any further, 

 and hence yields no amino-acids. Of this fact two alternative 

 explanations are offered (16). Either the proteins contain cer- 

 tain types of union (such as ether-like combinations and so forth) 

 which are not present in the synthetic polypeptids and which 

 are the only points of union which pepsin can attack; or else 

 the great length of the amino-acid chain in the proteins confers 



