THE PROTEINS AND THEIR METABOLISM 105 



The Fate of Amino Acids in the Tissues 



In the tissues the amino acids may undergo a number of changes, de- 

 pending upon the requirements of the cells. They may undergo de- 

 tfmination by a process of hydrolysis in which the NH 2 is replaced by an 

 hydroxyl radical, giving rise to the corresponding alcohol, forming hy- 

 droxylacids. 



CH 3 CH 3 



I I 



CHNH 2 + HOH - CHOH + NH, 



I , I 



COOH COOH 



Alanin Water Lactic acid Ammonia 



They may undergo deamination by a process of oxidation giving rise 

 to the corresponding keto or oxy-acids. 



CH 3 CH 3 



I I 



CHNH 2 + O ^ CO + NH 3 



COOH COOH 



Alanin Oxygen Pyruvic acid Ammonia 



They may be utilized by some cell in the synthesis of some organic 

 body like a ferment, product of internal secretion, serum albumin, serum 

 globulin, nucleoprotein, cell protein, etc. 



Urea Formation 



During the process of deamination ammonia is set free. This am- 

 monia is converted to its greatest extent into urea. We know that from 

 the fact that if an ammonia salt is fed to an animal most of it is excreted in 

 the form of urea (v. Schroeder, Salomon, Zaleski, Nencki and Pawlow), 

 and also from the fact that if a single amino acid is fed to an animal, all 

 of the nitrogen is excreted as urea (Levene and Kober ; 1909). We also 

 know that the liver is the organ which has the greatest power of convert- 

 ing ammonium salts into urea, and if amino acids are perfused through 

 the surviving liver, urea is formed (Fiske and Karsner, 1913; Fiske and 

 Sumner, 1914). 



