THE PROTEINS AND THEIR METABOLISM 107 



The Fate of the Non-Nitrogenous Fraction of the 

 Amino Acids 



The fate of the non-nitrogenous fraction- of the amino acid in the ani- 

 mal body has been the subject of careful study during the past fifteen 

 years, and the information obtained forms to-day one of the most interest- 

 ing chapters in physiological chemistry. 



Various methods have been employed in attacking this complex prob- 

 lem. The amino acids were fed to normal animals, phlorhizinized and 

 depancreatized animals, and the results studied. They were perfused 

 through surviving organs like liver, kidneys and muscles, and products 

 of their metabolism sought for. They were incubated with different ex- 

 tracts of tissues, with ground up tissues, and their changes studied. Chem- 

 ical substances that are related to the amino acids were fed to animals 

 with the object of determining along which path the catabolism of the 

 amino acid could possibly proceed. 



In summing up all the work, the following conclusions may be drawn :* 

 Glycocoll is completely converted into glucose (Ringer and Lusk, 1910). 

 After deamination either glycollic acid or glyoxylic acid may be formed. 



COH 



Glyoxylic acid 



CH 2 NH 



COOH 



^CH 2 OH 



Glycollic acid 

 COOH 

 Glycocoll 



Neither one of these intermediary substances, however, has been found 

 to give rise to sugar when administered to diabetic animals (Greenwald, 

 1918 (#) ; Ringer and Dubin, unpublished). 



Glycocoll also plays a role in the formation of one of the bile salts, 

 glycocholic acid, in which substance it exists combined with cholic acid. 

 This is the first instance where a product of protein catabolism may be 

 used by the cells in the synthesis of a definite compound that is essential 

 for the welfare of the animal body. 



Alanin is also completely converted into glucose. On deamination it 

 may give rise to lactic or pyruvic acid. 



'This subject is thoroughly reviewed in the Third Edition of Lusk's "Science of 

 Nutrition," pp. 184-207. 



