THE CHEMISTRY OF THE PROTEINS 89 
obtained up to the present time, as also their constitution in 
so far as it is known. 
(a) Monoaminomonocarboxylic 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 f-oxy-phenyl-a-aminopropionic 
acid oxyamino 
Serine or 8-oxy-a-aminopropionic acid acids. 
Cysteine or §-thio-a-aminopropionic acid : : 
Cystine or dicysteine, a-diamino-f-dithio- ee 
propionic acid. 
(b) Monoaminoaicarboxylic acids : 
Aspartic acid or aminosuccinic acid. 
Glutamic acid or a-aminoglutaric acid. 
(c) Diaminomonocarboxylic acids (hexone bases) : 
Ornithine or a-6-diaminovalerianic acid. 
Lysine or a-e-diaminocaproic acid. 
Arginine or a-amino-6-guanidine valerianic acid. 
Histidine or 8-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 Acrps 
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, 
