THE CHEMISTRY OF THE PROTEINS 89 



obtained up to the present time, as also their constitution in 

 so far as it is known. 



(a) Monoaniinomonocarboxylic acids : 



Glycine or amino-acetic acid. 



Alanine or a-aminopropionic acid. 



Valine or a-aminoisovalerianic acid. 



Leucine or a-aminoisocaproic acid. 



Isoleucine or a-aminomethylethylpropionic acid. 



Phenylalanine or phenyl-a-aminopropionic acid. 



Tyrosine or />-oxy-phenyl-a-aminopropionic " 



acid 

 Serine or /3-oxy-a-aminopropionic acid 

 Cysteine or /3-thio-a-aminopropionic acid 

 Cystine or dicysteine, a-diamino-/?-dithio 



oxyamino 

 acids. 



[thioamino 



propionic acid. acids. 



(b) Monoatninodicarboxylic acids : 



Aspartic acid or aminosuccinic acid. 

 Glutamic acid or a-aminoglutaric acid. 



(c) Diaminomonocarboxylic acids (hexone bases) : 



Ornithine or a-8-diaminovalerianic acid. 

 Lysine or a-e-diaminocaproic acid. 

 Arginine or a-amino-S-guanidine valerianic acid. 

 Histidine or /3-imidazoleaminopropionic acid. 



(d) Diaminooxymonocarboxylic acids : 



Diaminotrioxydodecanic acid. 



(e) Heterocyclic compounds : 



Proline or a-pyrrolidine carboxylic acid. 

 Oxyproline or oxy-a-pyrrolidine carboxylic acid. 

 Tryptophane or indoleaminopropionic acid. 



This list, appalling as it looks, is in reality comparatively 

 simple, and is evidence also as to the great complexity of the 

 proteins, which consist of a combination of these amino acids 

 in various proportions. 



I. The Amino Acids 



The amino acids as they are obtained from the proteins are, 

 with the exception of glycine, in the optically active form. The 

 synthetical products, on the other hand, are inactive or racemic, 



