34 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



Tyrosine is a little more complicated : it is oxyphenyl-alanine : 

 that is, instead of phenyl (C 6 H.,) in the formula of phenyl-alanine we 

 have now oxyphenyl (C 6 H 4 .OH). This gives us C 2 H 3 .(0 6 H 4 .OH) 

 NH 2 .COOH as the formula for tyrosine written one way, or 



OH 



CH 2 .CH.NH 2 ,COOH 



when written in the other way. 



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

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

 called indole. Tryptophane is the portion of the protein molecule 

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



/ PTT 

 decomposition called indole C 6 H / -^-pr' 



and scatole or methyl indole. Tryptophane is also the radical in the 

 protein molecule which is responsible for the colour test called the 

 Adamkiewicz reaction. 



We may sum up what we have learnt up to this point by enume- 

 rating the principal members of these three groups of ammo- 

 acids : 



1. The mono-amino-acids : glycine, alanine, leucine, amino- 

 valeric acid, asparagine, aspartic acid, glutamic acid. 



2. The di-amino- acids : lysine, ornithine, arginine, and histidine. 



3. The ringed amino-acids : phenyl-alanine, tyrosine, and 

 tryptophane. 



But this does not bring us to the end of the list of the cleavage 

 products of proteins, for we have still left several other groups most 

 of which are still more complex, and which we will therefore be 

 content with merely mentioning : namely 



4. Pyrimidine bases such as uracil, thymine and cytosine. 



5. Pyrrolidine derivatives. 



6. Cystine, a complex amino-acid in which sulphur is present, and 

 in which the greater part of the sulphur of the protein molecule is 

 combined. 



7. Ammonia. 



Our list now represents the principal groups of chemical nuclei 

 united together in the protein molecule, and its length makes one 



