fea 



THE PROTEINS 77 



physiological effects, and an important constituent of ergot. Phenylalanine 

 C 6 H 6 .CH 2 .CH.NH 2 .COOH, becomes phenylethylamine 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 



tures 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 



I I 



COOH CH 2 



I 

 COOH 



we may obtain the mono-amino-acids, 



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

 CH 2 NH 2 CH 3 



I I 



COOH CH.NH 2 



I 

 COOH 



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

 the position of the NlI 2 group may be varied. Thus, instead of alanine 

 we may have another amino-propionic acid, namely : 



CH 2 NH 2 



I 

 CH 2 



I 

 COOH 



This acid would be spoken of as ^-amino-propionic acid, alanine being 

 a-amino-propionic acid. This nomenclature is always used to distinguish 

 the position of the NH 2 group, so that we may have mono-amino-acids a, 

 /?, y, 6, s . . . and so on. Practically all the amino-acids which occur as 

 constituents of the protoplasmic molecule belong to the a group. 



On inspection of the formula of glycine it is evident that only one isomer 

 of this body is possible. In alanine, however, the carbon atom to which 

 NH 2 is attached, is asymmetric, since its four combining affinities are each 

 attached to different groups. Thus : 



C 



I 

 H C NH 2 



I 

 C 



In this case, therefore, there is a possibility of stereoisomerism, and alanine 

 must have an influence on polarised light. If the compound 



