Chemical Constituents of the Animal Body. 243 



products of the proteins consist chiefly of mono- and di- 

 amino-acids. As already stated, the latter, by virtue of 

 the fact that they contain two amino groups, have a basic 

 character, and can therefore be precipitated by certain 

 reagents generally employed for separation of alkaloids 

 from solution. It is, therefore, possible to separate the 

 monoamino from the diamino hydrolysis products. Most 

 proteins also yield when hydrolyzed, in addition to these 

 acids, a certain amount of ammonia. This is supposed to 

 be derived from acid amide groups existing in the mole- 

 cule. Some of the plant proteins, such as gliadin, yield 

 on hydrolysis a large amount of glutamic acid. This con- 

 tains only one amino group, but two carboxyl groups. Its 

 characters are, therefore, predominatingly acid. Never- 

 theless, gliadin itself is not markedly acid in character, 

 although it yields so much glutamic acid when hydrolyzed. 

 It is noteworthy, however, that it also yields relatively 

 large amounts of ammonia. It is not unreasonable to 

 assume, then, that the carboxyl groups of glutamic acid 

 which are not condensed in the peptide linkings with an 

 amino group exist condensed with ammonia in the form 

 of acid amide. On hydrolysis the acid amide group would 

 undergo scission to yield ammonia. 



Furthermore, when proteins are hydrolyzed with acids 

 there is nearly always formed a small amount of dark- 

 coloured insoluble residue, generally known as " hum in " 

 substance. The nitrogen of the hydrolysis products can 

 be distributed, therefore, amongst four groups namely, 

 the humin substances, the ammonia, the monoamino-acids, 

 and the diamino-acids. The nitrogen in these groups is 

 known respectively as " humin nitrogen," " amide nitrogen," 

 " monoamino nitrogen," and " diamino nitrogen." The 

 percentages of the total protein nitrogen contained in these 

 four groups are known as the " Haussmann numbers." 



