THE PROTEINS AND THEIR METABOLISM 107 



The Fate of the Non-Nitrogenous Fraction of the 

 Amino Acids 



The fate of the non-nitrogenous f ruction of the ainino acid in the ani- 

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

 vears. and the information obtained forms to-day one of the most interest- 

 in*: 1 Chapters in physiological chemistry. 



Various methods have been employed in attacking this complex prob- 

 lem. The ainino acids were fed to normal animals, phlorhizinizcd and 

 tiepanf-reatized animals, and the results studied. They were perfused 

 throuiih 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 ainino acids were fed to animals 

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

 ainino acid could possibly proceed. 



In summing up all the work, the following conclusions may be drawn: 1 

 f~i1>f'*fjcoU- is completely converted into glucose (Ringer and Lusk, 1910). 

 Afu.T deamination either glycollic acid or glyoxylic acid may be formed. 



COH 



| Glyoxylic acid 



_, COOH 

 CH 2 1S T H 2 ^ 



COOH 



^CHoOH 



Glycollic acid 



coon 



Glycocoll 



Xeither one of these intermediary substances, however, has been found 

 to -ive rise to sugar when administered to diabetic animals (Grcenwald, 

 11*1^ i r/) ; Ringer and Dubin, unpublished). 



f'ilycocoll also plays a role in the formation of one of the bile salts, 

 iilye'X-liolic acid, in which substance it exists combined with eholic acid. 

 TUH is the first instance where a product of protein eatabolism may be 

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

 t'<>r the welfare of the animal body. 



AJd.nin is also completely converted into glucose. On deamination it 

 may oi ve rise to lactic or pyruvic acid. 



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

 Nutrition," pp. 184-207. 



