730 



account for the iiifliience of tlie reaction on the enzvniic aclivity. 

 They suppose this activity to liave something to do with the electric 

 charge; they consider pepsin to be a so-called amphoteric substance, 

 whicli combines on either side of the iso-eiectric point witli bases 

 or acids, so that compounds are formed, which are in some measure 

 to be compared vvitii salts. 



According to them the compound containing acid becomes active; 

 when in solution it is. like salt, partly dissociated, and the pepsin- 

 ions are considered to be the active constituents. From this it .seems 

 to follow that with a greater amount of acid the activity must 

 increase beyond I he iso-electric point. As to a decrease with a still 

 greater amount of acid, Michaki.is sii[iposes that perhaps in that 

 case bivalent pepsin-ions may be formed without activity. He tries 

 to substantiate this view on the basis of experiments, just as he 

 does with other enzymes. He supposes the activity to vary in pro- 

 portion to the amount of pepsin-ions present in the ■solution. Now 

 it should be observed that the curve representing the activity of 

 enzymes, such as pepsin, as a function of the H-ion-coiu-entration 

 is comparatively only sligfitly typical and has, in still stronger acid 

 solutions, a rather abrupt rise up to tlie optimum and a less sudden 

 fall. All sorts of conjectures may induce one to suggest an approxi- 

 mate interpretation of such a curve, and it seems to me to be a 

 bold one to explain the phenomena in this case by supposing pepsin, 

 of which we really are still much in the dark, to form a salt wlien 

 combined with acids, and the electrically charged pepsin-ions to be 

 active in this process, and moreover by supposing bivalent-ions to 

 be educed when a second basic group of pepsin unites with acids, 

 and assuming these bivalent-ions to be inactive in contradistinction 

 to univalent-ions. This conjecture appears to be all the more hazard- 

 ous, as we had already denied the existence of the iso-electric point. 

 MiCHAEiJs also asserts that the question of identity or non-identity 

 of pepsin and chynu)siu may be solved in such a sense, that pepsin 

 combined with bases (consequently beyond the iso-electric point) 

 acts as chymosin, in which case Ihe pepsin-anions are supposed to 

 be inactive^) as such. 



With a view to further researches on the action of pepsin and 

 the nature of the action, it seemed to me to be of prime itnportance 

 to settle the question whether or not there is an iso-electric point 

 in pepsin, once for all. Should our previous results be contirmed, 

 it would be incumbent upon me to study the peculiar action of 



') (Jf. 'Die Wasserstoflionenkoiizentration." By L. Michaelis, (1914). 



