ENZYMES 187 



Electronegative (acid) pepsin digests best in an acid; and ampho- 

 teric (almost neutral) trypsin in an alkaline reaction. We may think 

 of enzymes as being amphoteric substances, in some of which the 

 positive charge predominates, in others, the negative; as a corollary 

 of this, pepsin dissolves in alkaline solution; in other words, the pepsin 

 is dissolved away from the substrate it would digest and is thus in- 

 activated; the reverse of this holds true for trypsin. Salivary dia- 

 stase seems entirely neutral, since saliva must fluidify as readily in 

 acid as in alkaline reaction. In some cases we observe a relationship 

 between the reaction of the substrate upon which a ferment is to 

 act and the ferment; thus, pepsin-rennin has a pronounced basic 

 character, casein an acid character, albumin in acid solution has a 

 basic character, and as such combines with acid pepsin; in alkaline 

 solution it has an acid character and so can unite with basic trypsin. 

 Consequently, we find here phenomena which I pointed out in my 

 experiments on the adsorption of dyestuffs, page 29. 



This difference in adsorbability is utilized in many cases for the 

 purification of enzymes. Thus L. MICHAELIS removed albumin from 

 mixtures of serum albumin and invertin by shaking them in acid 

 solution with kaolin; the invertin remained without loss of strength 

 in the albumin-free solution. E. ABDERHALDEN and F. W. STRAUCH 

 extracted pepsin from the stomach content of animals by means of 

 elastin and then recovered it from the elastin by means of water. 



Depending upon the reaction, decided differences were found 

 when enzymes were filtered through Chamberland filters. Accord- 

 ing to HOLDERER most of those studied by him passed through the 

 filter when they were neutral to phenolphthalein but they were held 

 back when neutral to methyl orange. HOLDERER attributes this 

 principally to the effect of adsorption by the filter mass. 



For a number of enzymes the course of the reactions was studied 

 and proved to be quite complicated. I refer to the investigations of 

 platinum sol by G. BREDIG and his pupils; of invertase and amylase 

 by V. HENRI; of lipase by M. BODENSTEIN and DIETZ and of emulsin 

 by P. JACOBSON, which are described by H. FREUNDLICH in his 

 "Kapillarchemie." It is conclusively shown in the publication of 

 W. S. DENHAM* from BREDIG'S Institute that among all the compli- 

 cated factors, it is the surface concentration which is of the greatest 

 importance for the acceleration of the reaction. 



In the case of gels, the greater the surface concentration becomes, or 

 in other words, the more swollen the substrate is, the better is the 

 opportunity offered an enzyme to enter the substrate. This obser- 

 vation can be made over and over again in the cases of enzyme 

 cleavage. E. KNOEVENAGEL* offers convincing proof of this fact. 



