28 NUTRITION OF FARM ANIMALS 



46. Hydrolysis of proteins. The simple proteins readily 

 undergo hydrolysis when acted upon by strong acids or alkalies, 

 or by various enzyms such as the pepsin of the gastric juice, 

 the trypsin of the pancreatic juice, etc. These various agents 

 effect a succession of cleavages and hydrations resulting in a 

 series of products of decreasing molecular complexity and in- 

 creasing solubility, ranging from very slightly modified proteins 

 through the so-called proteoses and peptones to still simpler 

 substances. 



47. Cleavage products of proteins. When the hydrolysis, 

 especially acid hydrolysis, of the simple proteins is pushed as 

 far as possible, there result a number of comparatively simple 

 crystalline substances which are qualitatively the same for all 

 proteins with a few exceptions, although the proportions of the 

 various products obtained from different proteins vary ma- 

 terially. It is believed, therefore, that the protein molecule is 

 built up of these final products of hydrolysis, the so-called 

 " building stones." 



These primary cleavage products of the simple proteins are 

 all a amino acids. One of the first of them to be isolated was 

 glycin or aminoacetic acid, represented by .the following for- 

 mula : 



CH 3 CH 2 NH 2 



I I 



COOH COOH 



Acetic acid Glycin 



The other cleavage products of the simple proteins may be 

 regarded as derived from glycin by the replacement of one 

 atom of hydrogen in the CH 2 group by various atomic group- 

 ings. In all of them the NH 2 group occupies the same position 

 in the molecule relative to the group COOH as in glycin, the 

 so-called a position. The atomic grouping 



CH - NH 2 



I 



CO -OH 



is therefore common to all of these bodies and determines their 

 general chemical behavior as well as that of the proteins from 

 which they are derived. 



