258 
Studies  on  Pepsin. 
S  Am.  Jour.  Pharm. 
(      April,  1921. 
solutions  of  these  samples  show  relatively  high  hydrogen  ion  con- 
centration. However,  the  reaction  of  the  i  :  40,000  sample,  which 
is  the  nearest  approach  to  the  pure  enzyme,  is  very  nearly  neutral 
(Ph  -j-  =6.oXio-7).  This  would  tend  to  disprove  the  view  held 
by  Jacoby  and  others  that  pepsin  is  an  acid. 
No  tests  were  made  on  the  straight  pepsin  solutions  with  satu- 
rated picric  acid,  sodium  chloride  and  ammonium  sulphate  solutions, 
and  also  none  with  potassium  ferrocyanide  in  acetic  acid  solution, 
since  the  results  with  all  of  these  reagents,  because  of  coagulable 
protein  would  be  positive,  and  practically  the  same  for  the  different 
strengths.  The  saturated  picric  acid,  Hopkins-Cole,  and  Millon's 
reagent  tests,  which  were  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  complex  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  i=3 
manifested  by  a  constant  tendency  in  the  purified  samples  to  ap- 
proach nea'rer  to  the  actual  character  of  proteins  with  increasing!  * 
proteolytic  activity,  and  is  accompanied  by  an  increase  in  material 
coagulable  by  heat.  From  the  fact  that  the  highest  strength  sam- 
ples still  give  strong  tests  with  Molisch  reagent,  it  may  be  possible 
that  the  pure  enzyme  is  a  conjugated  protein,  probably  a  glycopro- 
tein. 
Confirming  this  view,  the  mineral  matter  is  decidedly  less  in 
the  purified  samples  than  in  the  original  basic  material,  approaching 
almost  to  the  value  for  pure  proteins  in  the  case  of  the  strongest 
samples.    Both  sulphur  and  calcium  are  probably  unaffected  by  the 
