133 THE AMINO ACIDS 



the transformation of these substances into amino 

 acids in other words, amino acid synthesis occurs. 



Particular attention has been paid to the deter- 

 mination of the value of asparagine as a source of 

 nitrogen, one of the first investigators being Mer- 

 cadente, who believed that protein formation could 

 take place from asparagine, especially in plants. 

 Sachse believed that protein was formed from aspara- 

 gine by the simple addition of fatty aldehydes. On 

 the other hand, Loewi thought that in the presence of 

 carbohydrates protein was formed from asparagine 

 by a series of condensations. Zuntz suggested that in 

 herbivora asparagine was built up into protein by 

 bacteria in the intestine previous to utilization. This 

 latter view has been supported by numerous investi- 

 gators, some of whom state that protein-forming bac- 

 teria are widely distributed in nature and may act 

 very efficiently and quickly when in suitable envi- 

 ronment. The evidence available seems to speak 

 strongly in favor of the view that asparagine may 

 serve as source of nitrogen or act at least as a protein 

 sparer, as much as two-thirds of the protein in the 

 diet of herbivora being replaceable by asparagine. On 

 the other hand, several investigators claim that aspara- 

 gine cannot take the place of protein at all, hence, 

 cannot be used as a source of nitrogen and that even 

 the degree of protein sparing action that may be 

 exhibited by this amide is extremely limited. 



In a comparable manner it has been suggested that 

 various ammonium salts may also replace protein to 



