ijo  Chemistry  of  the  Proteins.  { AmAp°rnr,'i907!rm* 
the  a-amino  derivatives  of  acetic  acid  and  its  homologues,  contain- 
ing three,  five,  and  six  carbon  atoms  ;  phenylalanine,  closely  related 
to  analine,  but  containing  the  phenyl  group;  serine  and  tyrosine, 
the  simple  hydroxy  derivatives  of  alanine  and  phenylalanine  ;  aspartic 
and  glutaminic  acids;  prolin  and  oxyprolin,  derived  from  the  hetero- 
cyclic compound  pyrrolidine,  and  which  form  a  sort  of  bridge  be- 
tween the  proteins  and  the  alkaloids ;  the  diamino  acids,  ornithine, 
lysine,  and  arginine  ;  histidine  ;  tryptophan,  belonging  to  the  indol 
group;  and  cystin,  characterized  by  its  high  content  of  sulphur. 
It  does  not  follow  that  all  these  acids  must  occur  as  degradation 
products  of  every  protein,  in  which  the  molecule  would  be  terribly 
complicated  and  have  a  value  of  12,000-15,000,  or  from  fifteen  to 
twenty  times  that  of  the  fats ;  but  all  are  obtainable  from  the  ma- 
jority of  the  proteins,  and,  as  they  have  been  recognized  for  more 
than  fifty  years  as  the  corner-stones  of  the  protein  molecule,  it  is 
not  surprising  to  find  that  in  most  cases  the  structure  is  known  and 
a  complete  synthesis  has  been  effected.  With  the  exception  of 
glycocoll,  all  of  them  occurring  in  nature  are  optically  active, 
whereas  the  synthetic  products  are  inactive  ;  but  they  can  be  split 
into  optically  active  forms  by  the  well-known  methods  of  Pasteur. 
This  work  only  solves  the  smallest  portion  of  the  problem  of  the 
chemical  constitution  of  the  proteins,  for  it  is  much  more  difficult 
to  answer  the  question  in  which  way  are  the  molecules  of  the  amino 
acids  bound  together  ?  It  would  appear  that  the  solution  should  lie 
in  the  investigation  of  the  products  of  partial  hydrolysis  of  the 
proteins;  but  the  resulting  albumoses  and  peptones  are  mixtures  of 
very  similar  substances,  for  which  there  are  no  known  methods  of 
separation.  The  author  has  therefore  chosen  the  alternative  method 
of  investigation — namely,  the  synthesis  of  the  proteins  from  amino 
acids — and  has  attempted  to  thereby  produce  artificial  proteins 
similar  to  those  occurring  in  nature. 
SYNTHESIS  OF  "  THE  POLYPEPTIDES." 
Starting  with  two  molecules  of  glycocoll  (glycine),  it  is  seen  that 
condensation  can  take  place  between  the  carboxyl  group  of  one 
molecule  and  the  amino  group  of  the  second  molecule,  giving  rise 
to  a  new  substance  : — 
MH2-CH2  COjOH    HjNH  CH2-COOH  = 
H20  +  NH2-CH2-CO-NH-CH2-COOH  (1) 
