Am.  Jour.  Pharm.  \ 
April,  1919.  .  ' 
Studies  on  Pepsin. 
239 
of  the  strongest  sample  obtained  ( 1 : 40,000)  a  slight  amount  of 
hydrochloric  acid  was  used  in  the  preparation  of  the  other  strengths 
of  the  pepsin.  As  a  consequence,  2  per  cent,  aqueous  solutions  of 
these  samples  show  relatively  high  hydrogen-ion  concentration. 
However,  the  reaction  of  the  1  : 40,000  sample,  which  is  the  nearest 
approach  to  the  pure  enzyme,  is  very  nearly  neutral  (Ch+  =  6.oX 
io~7).  This  would  tend  to  disprove  the  view  held  by  Jacoby19  and 
others  that  pepsin  is  an  acid. 
Consideration  of  the  data  presented  in  Table  II  shows  that  the 
results  corroborate,  in  a  general  way,  the  analytical  data  already  dis- 
cussed. No  tests  were  made  on  the  straight  pepsin  solutions  with 
saturated  picric  acid,  sodium  chloride  and  ammonium  sulphate  solu- 
tions, and  also  none  with  potassium  ferrocyanide  in  acetic  acid  solu- 
tion, since  the  results  with  all  of  these  reagents,  because  of  coagul- 
able  protein  would  be  positive,  and  practically  the  same  for  the.  dif- 
ferent strengths.  Confirming  the  results  given  in  Table  I,  the  satu- 
rated picric  acid,  Hopkins-Cole,  and  Millon's  reagent  tests,  made  of 
the  filtrate  after  removal  of  coagulable  protein,  show  presence  of 
amino  acid  and  peptid  bodies  in  the  lower  strength  samples.  These 
gradually  disappear  so  that  only  traces  are  found  in  the  highest 
strength  sample  of  the  enzyme.  Both  saturated  sodium  chloride 
solution  and  potassium  ferrocyanide  in  acetic  acid  solution  gave 
negative  results,  indicating  absence  of  protoproteoses  in  the  filtrate 
from  coagulable  protein.  A  positive  reaction  was  obtained  in  every 
case  with  Molisch  reagent  showing  presence  of  glycoprotein,  or  its 
derivatives,  in  the  material.  It  is  significant  that  the  biuret  test  of 
the  filtrate  after  coagulation  of  protein  in  the  1  : 40,000  sample,  is 
negative.  This  would  indicate  that  practically  all  of  the  protein 
material  is  of  the  nature  of  coagulable  protein  or  even  more  com- 
plex in  its  protein  character. 
Discussion. 
A  review  of  the  data  presented  in  the  foregoing  seems  to  show 
that  in  the  purification  of  pepsin  there  is  a  gradual  elimination  of  the 
secondary  protein  derivatives  including  amino  acids.  This  is  mani- 
fested by  a  constant  tendency  in  the  purified  samples  to  approach 
nearer  to  the  actual  character  of  proteins  with  increasing  proteolytic 
activity,  and  is  accompanied  by  an  increase  in  material  coagulable  by 
19  Jacoby,  Biochem.  Z.,  vol.  4,  471,  1907. 
