CHAP. III.] 



AMJDO-ACIDS. 



231 



SECT. 10. THE AMIDO-ACIDS RESULTING FROM THE ACTION OF 

 TRYPSIN ON THE ALBUMINOUS BODIES. 



introductory ^ we replace an atom of H in the alcohol-radical 

 observations of certain acids by the monatomic NH 2 -, or amido- 

 on amido- gen-, group, amido-acids are formed. Thus by re- 

 aclds< placing in the case of acetic acid, CH 3 COOH, one H 



in the radical CH 3 by NH 2 , we obtain CH 2 (NH 2 )COOH, amido- 

 acetic acid, commonly known as glycocoll or glycocine, a body which 

 is one of products obtained from gelatin by long boiling with dilute 

 sulphuric acid, and which also results from the hydrolytic decom- 

 position of hippuric and glyco-cholic acids. 



Another example of an amido-acid derived from a fatty acid is 

 afforded by the body leucine, to be immediately considered in detail, 

 and which is an amido-caproic acid. 



In the case of each individual acid, the method by which it can 

 be obtained, as well as its special characters, and more important 

 compounds and reactions, will be described with sufficient fulness. 



Methods of We shall have to point out that the differences in 



general appli- the solubility of the amido-acids in water and absolute 

 r tne alcohol, respectively, afford a ready means of separat- 

 ing certain of the amido-acids (leucine, and tyrosine) which 

 are principal products of pancreatic proteolysis. In ad- 

 dition to these there are, however, others, some of which 

 have already been separated, and others await investigation. The com- 

 pounds with Cu aid us in this search. All the amido-acids form very 

 sparingly soluble and definite crystalline compounds with copper, which 

 are readily obtained by boiling the aqueous solution of the acid or acids 

 with properly precipitated cupric hydrate Cu(OH) 2 , filtering and allowing 

 the solution to cool ; unless the solution have been very dilute the 

 Cu compound will then separate. These compounds may be purified, the 

 amount of Cu which they contain determined, and, besides, they may be 

 decomposed by H 2 S, and the amido-acid obtained in a pure condition 1 . 



separation of 

 the amido- 

 acids. 



Two import- Istly. When treated with nitrous acid the whole of 



at general re- their ^ i s evolved in the gaseous form and an oxy-acid 



actions of ami- . . 



do-acids, 



is formed, thus : 



(1) CH 2 (NH 2 )COOH 



Glycocine. 



HN0 2 = CH 2 (OH)COOH + N 2 + H 2 0. 



V / 



Oxyacetic or glycollic acid. 



1 Refer to the individual amido-acids for details as to the composition, preparation, 

 purification and decomposition of the Cu compounds. 



