738 



Physiology. — ''Further rg.seiirches on pure j)ep.iiii.." By Dr. W. E. 

 RiNGEu. (Co mm imitated bv Prof. C. A. Pekelharing.) 



(GommunicatoJ in the meeting of September 2G, l'.)15). 



Some yeaivs ago Pkkei.haring and myself') found that pure ])epsiii 

 lias not a so-called iso-electric point, that is to say, not with any 

 concentration of hydrogen-ions has it a minimal electric charge 

 with opposite charges on cither side of this H-concentration. Pepsin 

 always appeared to be electro-negative and ever to move towards 

 the anode in the electric field. This result conflicted with the ex- 

 perience of MiCHAELis and Davidsohn', who found in their pepsin 

 an iso-electric point at a concentration Cii= 5.5 X 10~^ (pii=^ 4.26). 

 We found, however, that when we add protein or albumoses to our 

 pepsin, the enzyme behaves a? in the experiments of Michaelis and 

 Davidsohn. It then educes an iso-electric point, more or less distinct 

 according to the amount of protein added. This may also happen 

 when the enzyme has been prepared under unfavourable circum- 

 stances. Michaelis and Daviusohn made their experiments with 

 Grübler's pepsin, an impure commercial preparation. The impurities 

 of their pepsin are obviously responsible for their results. 



In the meantime Michaklis and Mendelssohn') have brought forward 

 another publication, in which tiiey assert that pepsin is an enzyme, 

 obeying the laws of dissociation and of which the free cations act 

 proleolitically. We know now, especially after the important ex- 

 periments by SöRENSEN, that the H-ion-concentration is of great 

 importance for the action of hydrolitic enzymes. A number of enzymes 

 have been examined in this respect; it appeared that there is a 

 maximum action at a definite reaction; on either side of this optimal 

 H-ion-concentration the action decreases at first slowly, then rapidly. 

 SoRENSEN had already observed this plienomenon in his researches 

 on pepsin and had already determined the optimum. He cautiously 

 avoids accounting for this plienomenon and only states that the 

 location of the optima! reaction depends to some extent on circum- 

 stances ; it shifts towards greater Cn in prolonged digestion experi- 

 ments, which SöRENSEN ascribes to the fact that pepsin is rendered 

 inactive in .«olutions with small H-ion-concentrations. The longer 

 the period of digestion, the greater the effect of this lack of activity. 



MiCHAEi.ts and his co-workers, however, have endeavoured to 



') Zeitschr. f. physiol. Chem. Bnd. 75, S. 'ASi (1911), 

 -} liochem. Zeitschr. Bnd. 2S, S. 1 (1910j. 

 3) Liochem. Zeitschr. Bnd. 65, S. 1 (1914). 



