CHEMICAL MECHANICS OF SYNTHESIS 443 



tures is shewn by the fact that if a sufficiency of dry pepsin * be 

 added to the unconcentrated products of the complete peptic 

 hydrolysis of N/10 sodium caseinate synthesis will occur at 36 

 degrees. I have found about 2 grams of pepsin (Gruebler's 

 puriss. sice.) per hundred cubic centimeters sufficient for this 

 purpose. That the equihbrium is still further shifted by a rise 

 in temperature is shown by the following experiment : 



To 300 cc. of the unconcentrated products of the peptic hy- 

 drolysis of iV/10 sodium caseinate were added 6 grams of dry 

 pepsin. After 48 hours at 36 degrees (in the presence of excess 

 of toluol) a precipitate had formed, while the supernatant fluid 

 remained somewhat opalescent; after 6 days the supernatant 

 fluid was quite clear and a bulky precipitate lay at the bottom 

 of the flask; the clear fluid was now decanted from the precipi- 

 tate and divided into two parts; the one was kept at 36 degrees 

 and the other at 65 degrees; within 8 hours a precipitate had 

 formed in the latter, the supernatant fluid being strongly opal- 

 escent, while the part of the solution which remained at 36 

 degrees had developed no trace of precipitate or opalescence 

 after a period of two weeks. It is clear, therefore, that the 

 system had arrived at equilibrium at 36 degrees before the fluid 

 was decanted, since this fluid must have been "saturated" with 

 paranuclein A (soluble in these acid solutions only to an unde- 

 tectable extent) and any further formation of paranuclein A 

 would have resulted in an increase in opalescence if not in actual 

 precipitation. This did not occur, however, even during a period 

 of two weeks. Yet at 65 degrees a faii'ly abundant precipitate 

 was produced within 8 hours. 



It is cleai', therefore, that in the enzymatic synthesis of para- 

 nuclein A a marked shift in equilibrium is involved, and we 

 must therefore definitely abandon the \dew that pepsin is a 

 "typical" catalysor which does not, to an appreciable extent, 

 participate in the reactions which it catalyses. 



The existence of a similar influence of trypsin upon the equi- 

 librium in protein solutions is possibly indicated by the investi- 

 gations of Walters (73), who has shown that whereas the time- 

 relations of the hydrolysis of casein by trypsin are very accurately 



* Dry, that is to say, not in solution, for otherwise water is added to the 

 system and the solution of products is actually diluted by the addition of the 

 ferment. 



