Am.  Jour.  Pharm.  ) 
April,  1921.  5 
Studies  on  Pepsin. 
259 
purification,  but  there  is  a  decided  decrease  in  the  phosphorus  con- 
tent and  seemingly  a  total  elimination  of  chlorides.  Other  than 
the  increase  which  would  obtain  by  removal  of  non-nitrogenous 
impurities,  there  is  probably  not  much  change  in  the  content  of 
total  nitrogen  as  a  result  of  pepsin  purification. 
The  manner  in  which  the  a-amino  acids  decrease  as  the  pro- 
teolytic activity  increases  is  striking,  and  seems  to  be  almost  pro- 
portional in  amount.  It  is  noteworthy  that  the  small  amount  of 
a-amino  acid  present  in  the  sample  testing  1  :  40,000  (0.61  per  cent.) 
very  nearly  approaches  the  value  for  this  factor  due  to  lysin  ag 
found  present  by  Van  Slyke  and  Birchard  in  most  proteins  analyzed 
by  the  nitrous  acid  method. 
Results  of  optical  activity  determinations  are  apparently  of  no 
significance,  since  the  same  values  are  obtained  with  several  dif- 
ferent strengths  of  pepsin.  As  already  mentioned  above,  the  reac- 
tion in  aqueous  solution  of  the  strongest  (1  : 40,000)  pepsin  is 
significant  because  of  its  very  slight  acidity.  It  would  seem  very 
likely,  that  the  concentration  of  hydrogen  ions  in  solutions  of  the 
pure  enzyme,  when  isolated,  will  probably  show  only  the  slight 
acidity  comparable  to  that  given  by  other  proteins. 
In  connection  with  the  assays  of  proteolytic  strength  by  the 
U.  S.  P.  method,. it  was  deemed  of  interest  to  make  a  comparison  of 
the  rennetic  power  of  the  different  samples.  It  is  a  significant  fact 
that  throughout  the  entire  series,  from  1  :  2000  to  1  :  40,000,  the 
rennetic  activity  and  proteolytic  strengths  are  found  to  go  hand 
in  hand. 
CONCLUSIONS. 
1.  The  purification  of  pepsin  seems  to  consist  in  the  elimination 
of  secondary  protein  derivatives  including  a-amino  acids. 
2.  Calcium  and  sulphur  appear  to  be  unaltered  as  a  result  of 
purification,  but  phosphorus  is  materially  reduced.  Chlorides  are 
seemingly  entirely  removed. 
3.  Aqueous  solutions  of  pepsin,  after  purification,  show  no 
material  change  in  optical  activity.  A  sample  of  high  digestive 
power  (1  :  40,000),  shows  a  reaction  very  nearly  neutral. 
4.  Pepsin  tends  to  approach  nearer  to  the  actual  character  of 
a  protein  (possibly  a  glycoprotein)  with  increasing  proteolytic 
activity. 
