741 



in handling. Still, however indifferent cane-sngar seems to be and 

 most likely will be in these experiments, it niay be objected that 

 without this substance the process might have been different. I insist 

 npon saying therefore, that in an initial set of experiments, without 

 any addition, the I'esults were quite the same, except an occasional 

 disturbance in one case. As in this set of experiments the specific 

 gravity of pepsin-solution and of the side-fluid was about the same, 

 the disturbance must have been due to a slight rise of the specific 

 gravity of the latter generated by the current, which necessarily 

 engendered a streaming of the fluids. The results obtained with 

 pepsin-solutions to which sugar had been added, are given in the 

 following table. It will be seen that in every experiment the movement 

 of pepsin was anodal ; consequently it was charged negatively. In 

 an earlier |)ublicatiou we have already demonstrated that by the 

 addition of [yrolein or albumoses an iso-electric point was in some 

 sense brought forth. I now repeated these experiments with albumoses, 

 which confirmed my former results, only the addition of the albumoses 

 had to be greater than before, which niust be ascribed to the higher 

 degree of purity of the pepsin. 



This evidence goes to show that with a sufficient quantity of 

 albumoses the movement is reversed, though it never becomes 

 quite cathodic. It is remarkable that amino-acids do not seem to 

 unite with pepsin, although a combination (or an adsorption) was 

 expected in view of the opposite electrical charge. 



We now know for certain, therefoi'e, that pepsin has not an iso- 

 electric point. This being settled, something else requires considera- 

 tion, which at first sight seems to clash with oui' experience, viz. 

 the existence of a minimal solubility of the pure pepsin iji the 

 neighbourhood of the neutral point (pji^4 — 5). However, we need 

 not wonder at this. Pepsin, surely, must not be bracketed with 

 ordinary proteins. It difïers from them altogether, for instance 

 by the remarkable property to coagulate in hydrochloric acid 

 solution, when heated rapidly (Pkkki.hauing). Still, this peculiar 

 behaviour of pejjsin (no iso-electric point and none the less a 

 mininuxl solubility) drew my attention. I have tried to learn 

 more about this. Pekei.haring has already put forward the hypo- 

 thesis that pepsin might be a combination of the real enzyme and 

 protein'). Granting this to be true, the behaviour in the electric 

 field can be accounted for, when the compound is decomposed in 

 acid solution. If it is not deconqjosed in a veiy faint acid 



') Archives des Sciences biologiques. Tome XI, p. 37 (1904). 



