OH. XXVIII.] 



AMINO-ACIDS 



419 



If the H placed lowermost in the above formula is replaced by 

 CH 2 CH . NH., . CO OH, we obtain the formula of phenyl-alanine : 



CH 2 . CHNH 2 COOH 



the remainder of the benzene ring, which is unaltered, being repre- 

 sented as usual by a simple hexagon. 



Tyrosine is a li ttle more complicated ; it is oxyphenyl-alanine ; 

 that is, instead of phenyl (C G H 5 ) in the formula of phenyl-alanine, 

 we have now oxyphenyl (C 6 H 4 . OH) ; this gives us 



C 2 H 8 



(C 6 H 4 .OH)NH 2 .COOH 



as the formula for tyrosine written one way, or 



HO 



CH 2 . CHNH 2 . COOH 



when written in the other way. Tyrosine crystallises in collections 

 of very fine needles (see fig. 313). 



Tryptophane is more complex still ; it is indole amino-propionic 

 acid : that is, amino-propionic acid united to another ringed deriva- 

 tive called indole. Tryptophane is the portion of the protein 

 molecule which is the parent substance of two evil-smelling products 

 of protein decomposition called indole and scatole or methyl indole. 

 Indole is a combination of the benzene and pyrrol rings as shown 

 below : 



CH 

 /I 

 HC 



HC\ 



/CH 



Tryptophane is the radical in the protein molecule which is 

 responsible for the colour test called the Adamkiewicz reaction. 



In all the preceding cases, there is only one replacement of an 

 atom of hydrogen by NH 2 ; hence they may be- all grouped together 

 as mono-amino-acids. 



Passing to the next stage in complexity, we come to another group 



