THE MONO-AMINO-ACIDS. 81 



Aspartic acid is a-amino-succinic acid : 



COOH.CH.(NH 2 ).CH 2 .COOH. 



Glutaminic acid has the formula : 



COOH.CH(NH 2 ).CH 2 .CH 2 .COOH. 



The former is Isevorotatory, the latter dextrorotatory. Their 

 amides, viz., asparagin, CONH 2 and glutamin, CONH, 



CHNH 2 CHNH 2 



CH 3 CH 2 



COOH, CH, 



COOH, 



occur widely distributed in the vegetable world, but do not occur in 

 animal tissues. 



Cystin is the disulphide of /9-cystein, -amino-/?-thiolactic acid 

 viz., a-diamino-/9-dithio-dilactic acid : 



CH 2 S-S CH, 

 CH(NH 2 ) CH(NH 2 ) 

 COOH COOH. 



Phenyl-alanin and tyrosin are members of the aromatic series. 

 Phenyl-alanin corresponds to a phenyl-ct-amino-propionic acid : 



C 6 H 6 .CH 2 .CH(KE 2 ).COOH ; 



it occurs in the albumins as the laBVorotatory form. 



Tyrosin is a corresponding oxy-acid, viz., p-oxyphenyl-alanin or 

 j>oxyphenyl-a-amino-propionic acid : 



C 6 K 4 .OH.CH 2 (NH 2 ).COOH. 



Both the dextro- and the Isevorotatory form occur, the latter pre- 

 dominating. 



a-pyrrolidin-carbonic acid, tryptophan, and oxypyrrolidin-carbonic 

 acid are heterocyclic compounds. 



Both a-pyrrollidin-carbonic acid (prolin) and the corresponding 

 oxy-compound (oxyprolin) are now recognized as primary split 

 products of the albuminous molecule. Prolin is represented by the 

 formula : 



CH, CH, 



CH, CH.COOH, 



while oxyprolin is C 5 H 9 NO 3 . 

 6 



