1 66 NUTRITION OF FARM ANIMALS 



bearing a more or less close relation to the fatty acids and to- 

 gether constituting the " non-nitrogenous residue " of the 

 proteins (229). 



It is important to note that these non-nitrogenous products 

 contain the larger share of the chemical energy of the original 

 proteins, the ammonia carrying off but little and both the di- 

 gestive cleavage and the deaminization being nearly isothermic 

 processes. The cleavage and deaminization of proteins, there- 

 fore, do not necessarily involve a destruction of their nutritive 

 value and the excretion of a given amount of nitrogen in the 

 urine is not to be regarded as indicating the total destruction 

 of a corresponding amount of protein. It has ceased to exist as 

 protein, but its non-nitrogenous residue is made up of substances 

 which are closely related chemically to both the carbohydrates 

 and fats, and which, like these, may be katabolized to supply 

 energy. 



234. Deaminization reversible. Since deaminization in the 

 body appears to be an enzymatic reaction, it is natural to in- 

 quire whether in this case, as in the other enzymatic reactions 

 already considered, there is any evidence that the reaction is 

 a reversible one. 



So far as direct experiments with deaminizing enzyms are 

 concerned, no such evidence has been produced, but Knoop l 

 andEmbden and Schmitz 2 have demonstrated a fact of funda- 

 mental significance in metabolism, viz., that amino acids may 

 be formed in the body from ketonic or hydroxy acids and am- 

 monium salts. In other words, the animal body can manufac- 

 ture some at least of the " building stones " of the proteins, 

 and from the latter presumably the proteins themselves (226), 

 out of the ammonium salts of the corresponding ketonic or 

 hydroxy acids. The full significance of this comparatively 

 recent discovery is not yet fully apparent. The question of the 

 utilization of ammonium salts will be considered later. In 

 this connection the important fact is that these results indicate 

 that the reaction, or series of reactions, by which deaminization 

 takes place is reversible, so that the whole process of protein 

 metabolism may be represented schematically as follows : 



-04-- ^. A -j -> [ Organic acids 

 Proteins X Ammo acids 2. S 



[ Ammonia 



1 Ztschr. Physiol. Chem., 67 (1910), 489. 2 Biochem. Ztschr., 29 (1910), 423. 



