ORDER IN WHICH AMINO-ACIDS ARE SPLIT 387 



the ferment. The substrate of this second reaction being, however, 

 a product of the first, its velocity is at first low, since the sub- 

 strate concentration is low; but as velocity of the first reaction 

 declines, owing to the consumption of the substrate, that of 

 the second reaction increases, owing to the increase in the mass 

 of its substrate. 



When however, instead of trypsin, yeast endotryptase is em- 

 ployed as the ferment, not the glycyl-alanin bond but the leucyl- 

 glycyl bond is first attacked. There is thus no question but 

 that the mode of action of yeast endotryptase is quite different 

 from that of trypsin and a means of sharply distinguishing be- 

 tween different enzjmies is clearly indicated. It will also be 

 evident that in digests containing a mixture of proteolytic enyzmes, 

 such as occurs in tissue-extracts, etc., the conditions of hydrolysis 

 must be much more complex than they are in digests containing 

 only a single enzyme; since under such circumstances two or 

 more parallel reactions may be occurring, possessed of different 

 specific velocities, at each step in the progressive hydrolysis of 

 of the peptid or protein. 



Glycyl-d-alanyl-glycin is first attacked by trypsin at the glycyl- 

 d-alanyl junction, by yeast endotryptase at the alanyl-glycin 

 junction; d-alanyl-glycyl-glycyl-glycin is first attacked by trypsin 

 at the glycyl-glycin junction. 



LITERATURE CITED 



(1) Abderhalden, E., and Brahm, C, Zeit. f. physiol. Chem., 57 (1908), 



p. 342. 



(2) Abderhalden, E., and Collaborators (Babkin, Bergell, Bloch, Damm- 



hahn, Deetjen, Gigon, Heise, Hunter, Kautsch, Koelker, Lussana, 

 Manwaring, McLester, Medigreceanu, Michaelis, Oppler, Pilliet, 

 Pincussohn, Pringsheim, Rona, Samuely, Schittenhelm, Teruuchi, 

 Walther, Weichardt). Zeit. f. physiol. Chem., 39 (1903), p. 9; 

 46 (1905), pp. 176 and 187; 47 (1906), pp. 159, 346, 359, 391, 466; 

 48 (1906), pp. 537, 557; 49 (1906), pp. 1, 21, 26, 31; 51 (1907), pp. 

 294, 308, 334; 54 (1908), p. 363; 55 (1908), pp. 371, 377, 384, 390, 

 395,416; 57 (1908), p. 332; 59 (1909), p. 249; 60 (1909), p. 415; 61 

 (1909), p. 200; 62 (1909), pp. 120, 136, 145, 243; 66 (1910), pp. 265, 

 277; 68 (1910), p. 471. 



(3) Abderhalden, E., and Gigon, A., Zeit. f. physiol. Chem., 53 (1907), 



p. 251. 



(4) Abderhalden, E., and Koelker, A. H., Zeit. f . physiol. Chem., 51 (1907), 



p. 294. 



