794 PHYSIOLOGY OF DIGESTION AND SECRETION. 



6. Leucin (a-amino-isobutylpropionic acid) : 



CHCH 2 CHNH 2 COOH. 



Two other isomeric forms of this compound have been obtained from the 

 split products, namely: 



Isoleucin (methyl-ethyl a-aminopropionic acid) : 



CH 3 \ 



>CHCHNH 2 COOH. 

 C 2 H 5 / 



Normal leucin norleucin (a-aminocaproic acid) : 

 CH 3 CH 2 CH 2 CH 2 CHNH 2 COOH. 



7. Aspartic acid (aminosuccinic acid) : 



COOHCHNH 2 CH 2 COOH. 



8. Glutaminic acid: 



COOHCHNH 2 CH 2 CH 2 COOH. 



9. Lysin (a- e-diaminocaproic acid) : 



CH 2 NH 2 CH 2 CH 2 CH 2 CHNH 2 COOH. 



10. Arginin (guanidin a-aminovalerianic acid) : 



/NH 2 

 C=NH 

 \NHCH 2 CH 2 CH 2 CHNH 2 COOH. 



II. AMINO-ACIDS CONTAINING A BENZENE (HOMOCYCLIC) OR A HETERO- 

 CYCLIC NUCLEUS. 



These compounds may be regarded as a-aminopropionic acids in which a 

 hydrogen attached to the /3-carbon atom is substituted by a benzene, an indol, 

 or an imidazol group. 



1. Phenylalanin (a-amino-|8-phenylpropionic acid): 



C 6 H 5 CH 2 CHNH 2 COOH, or 

 H 



S\ 



HC CH 



HC CH 



% / 



C . CH 2 CHNH 2 COOH. 



2. Tyrosin (a-amino--para-oxyphenylpropionic acid) : 



C 6 H 4 OHCH 2 CHNH 2 COOH, or 

 OH 



S\ 



HC CH 

 HC CH 



C . CH 2 CHNH 2 COOH. 



