16 THE AMINO ACIDS 



Aspartic Acid Amino-succinic acid. 



CH2.COOH 

 CH.NH2.COOH 



Asparagine, the amide of aspartic acid, has been known since 

 1806, having been isolated from asparagus juice by Robiquet 

 and Vanquelin. Upon boiling asparagine with lead hydroxide 

 Plisson in 1827 obtained aspartic acid. In 1868 aspartic acid 

 was shown by Ritthausen to be present as a product of hydro- 

 lytic cleavage of vegetable proteins. In a similar manner 

 Kreussler obtained it upon hydrolysis of animal proteins and 

 in 1874 it was isolated by Radziejeioski and Salkowski from 

 a tryptic digestion of protein. Its structure was established in 

 1887. 



Glutamic Acid (Glutaminic Acid) o-amino-glutaric acid. 



CH 2 



H 2 .COOH 

 .NH 2 .COOH 



Although glutamic acid was first separated from a hydrol- 

 ysis of wheat gluten in 1866 by Ritthausen its structure was 

 not shown until 1890. Ritthausen demonstrated that it was an 

 amino acid and from this fact together with its origin from 

 gluten gave it the name of glutaminic acid. Glutamic acid 

 was later shown to arise from hydrolytic cleavage of proteins 

 of animal origin as well as from those derived from the vege- 

 table kingdom. 



Lysine. a-, e,-diammo-caproic acid. 



H2N.CH 2 .CH 2 .CH2.CH2.CH.NH2.COOH. 



Lysine is widely distributed as a protein constituent. It 

 was first isolated from casein by Drechsel in 1889. Ellinger 



