THE PROTEINS . 85 



off carbon dioxide from the amino-acids. Thus, the diamino-acid, 

 lysine, 



CH 2 NH 2 CH 2 NH 2 



CH 2 CH 2 



I I 



CH 2 becomes CH 2 pentamethylene diamine. 



CH 2 CH 2 



CH.NH 2 CH 2 NH 2 



COOH 



Tyrosine becomes p. oxyphenylethylamine, a substance having 

 marked physiological effects, and an important constituent of ergot. 

 Phenylalanine C 6 H 5 . CH 2 . CH . NH 2 . COOH, becomes phenylethyla- 

 mine C 6 H 5 .CH 2 .CH 2 .NH 2 . These reactions are therefore of value 

 in determining the exact grouping of the atoms in the more complex 

 of the proximate constituents of the proteins. 



Since all the known disintegration products of the proteins belong 

 to the class of amino-acids, it may be of value to point out some of the 

 distinguishing features of this class of bodies. 



PROPERTIES OF AMINO-ACIDS. An amino-acid is derived 

 from an organic acid by the replacing of one atom of hydrogen by the 

 amino group NH 2 . Thus from the acids, 



acetic acid propionic acid 



CH 3 CH 3 



COOH CH 2 



COOH 

 we may obtain the mono-amino-acids, 



amino-acetic acid alanine or a-amino-propionic acid 



CH 2 NH 2 CH 3 



COOH CH.NH 2 



COOH 



It will be noticed that in the fatty acids with more than two atoms 

 of carbon the position of the NH 2 group may be varied. Thus, 



