CHEMICAL MECHANICS OF SYNTHESIS 443 



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

 added to the unconcentrated products of the complete peptic 

 hydrolysis of N/W 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 equilibrium 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 N/ 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 fairly abundant precipitate 

 was produced within 8 hours. 



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

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

 must therefore definitely abandon the view 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. 



