Aru.  Jour.  Pharm.  ) 
February,  1915.  J 
The  Function  of  Enzymes. 
67 
pressure,  but  which,  when  thus  obtained,  produced  alcohol  and  carbon 
dioxide  from  sugar  in  exact  accordance  to  the  chemical  equation 
which  had  long  been  used  to  represent  the  fermentation.  Thus  it 
was  shown  that  intra-cellular  enzymes  exist,  and  we  now  believe  that 
many  processes  taking  place  in  living  cells — perhaps  all  the  processes 
— are  the  results  of  enzyme  activity. 
Since  the  chemical  nature  of  enzymes  is  so  largely  unknown, 
we  can  classify  them  only  by  their  action  on  various  compounds. 
It  is  possible,  however,  to  group  them  into  the  four  classes  of  hy- 
drolyzing,  or  causing  the  addition  of  water  to  certain  substances. 
Most  enzymes  acting  on  carbohydrates  are  of  this  class.  So  also 
are  those  that  affect  fats,  and  the  majority  of  those  producing  known 
proteolytic  changes.  These  are  best  represented  in  the  processes  of 
digestion.  A  second  group  are  the  Zymase,  or  those  producing  the 
splitting  of  bodies  into  simpler  cleavage  products  without  any  hy- 
dration.   The  alcoholic  fermentation  is  the  best  known  of  this  class. 
The  remaining  two  classes  are  the  oxidizing  and  reducing  en- 
zymes, producing  the  types  of  change  implied.  Of  the  former,  the 
production  of  vinegar  is  a  familiar  example,  alcohol  being  oxidized 
to  acetic  acid  by  an  oxidase  produced  by  the  acetic  bacteria.  Such 
familiar  changes  as  the  darkening  of  freshly-cut  surfaces  of  fruits 
(apples)  or  the  quick  change  of  color  when  mushrooms  and  toad- 
stools are  broken,  also  belong  to  this  category.  The  reduction 
processes  are  of  enormous  variety  in  nature,  both  in  plant  and  animal 
life.  While  typically  distinguished  by  the  reduction  of  hydrogen 
peroxide  to  water  and  oxygen,  these  Katalases,  as  they  are  called, 
may  also  reduce  sulphates,  nitrates,  and  various  coloring  matters,  as 
well  as  other  compounds.  Upon  the  activity  of  enzymes  may  depend 
all  the  complex  series  of  changes,  oxidations,  reductions,  synthetic 
and  analytic  changes  which  characterize  the  processes  of  growth  and 
decay,  renovation  and  destruction  in  the  cell  and  in  tissues.  The 
phenomenon  on  intra-cellular  fermentation  seems  to  be  closely  linked 
with  enzymic  activity,  and  the  building  up  and  breaking  down  of 
protoplasm  itself  is  intimately  connected  with  intra-cellular  changes 
and  energy  liberation. 
There  is  reason  to  believe  that  some  enzyme  actions  are  like 
organic  chemical  reactions,  reversible.  Thus,  maltase  will  split 
maltose  into  two  moleculars  of  dextrose  under  the  ordinary  condi- 
tions of  action.   If,  however,  we  add  maltase  to  concentrated  dextrose 
