DIGESTION AND ABSORPTION IN THE INTESTINES. 727 



groups (NH 2 ) in direct union with carbon. The nitrogen of the 

 protein molecule appears in the split products in this form and also 

 partly as ammonia compounds. Some of these bodies are mon- 

 amino-acids, that is, contain one NH 2 group, such as leucin, 

 tyrosin, glycocoll and include substances belonging to the fatty 

 acid series (aliphatic series), the benzene or carbocyclic series, 

 and the heterocyclic series. 4 ' Others are diamino-acids, containing 

 two NH 2 groups. These latter include lysin, histidin, and arginin, 

 which, on account of their basic properties, are frequently described 

 as nitrogenous bases, and sometimes as the hexon bases, since 

 they contain six carbon atoms. 



The chemical formulas for the best known of these bodies are as follows. 

 For their properties and chemical relationships reference must be made to 

 the text-books on physiological chemistry (see also Appendix, Chemistry of 

 Proteins) : 



I. MONAMINO-BODIES. 

 FATTY ACID SERIES. 



Glycocoll or ammo-acetic acid: CH 2 NH 2 COOH. This product is ob- 

 tained in especially large quantities by hydrolysis of gelatin. Accord- 

 ing to Abderhalden,* it is split off with difficulty by trypsin. 



Alanin or a-aminopropionic acid: CH 3 CHNH 2 COOH. 



Ammovalerianic acid: ^ 3 ^CHCHNH 2 COOH. 



Leucin or aminocaproic acid: 3 ^CHCH 2 CHNH 2 COOH. As stated 



above, this compound was one of the first end-products of protein 

 hydrolysis that was recognized. It may be obtained readily in 

 crystalline form. 



CHNH 2 COOH 

 Aspartic or aminosuccinic acid : 



CH 2 COOH. 

 Glutaminicacid: CH 2 (NH 2 COOK 



BENZENE OR AROMATIC SERIES. 



Tyrosin (para-oxyphenylaminopropionic acid) : C 6 H 4 OH . CH 2 . CHNH 2 - 

 COOH. This substance was also among the first recognized prod- 

 ucts of protein hydrolysis It occurs early in the process of pan- 

 creatic digestion, and is easily obtained in crystalline form from 

 the digested mixture. It is especially interesting because of the 

 presence of a benzene nucleus, thus giving proof that the benzene 

 grouping occurs normally in the protein molecule. 



Phenylalanin (phenylaminopropionic acid) : C 6 H 5 CH 2 CHNH 2 COOH. This 

 benzene derivative is, according to Abderhalden, split off from the 

 protein with difficulty by the action of trypsin, although readily 

 produced by acid hydrolysis. 



PYRROL AND INDOL SERIES. 



CH 2 CH 2 

 o-Pyrrolidincarboxylicacid: CH 2 CHCOOH. This substance, discovered 



NH 



* Abderhalden, " Zeitschrift f. physiol. Chemie," 44, 17, 1905. Consult 

 tor general description of the digestion of proteids. 



