THE PROTEINS AND THEIR METABOLISM 115 



Tryptophan does not give rise to glucose nor to acetone bodies. It is 

 one of the indispensable amino acids (see page 125). It may be con- 

 sidered the mother substance of thyroxin, the principal substance of the 

 hormone of the thyroid gland (Kendal, 1919 (c)). 



H 

 H/\ 



-CH,-CHNH,-COOH 



IH 

 IH/\. 



-CH 2 -CH 9 -COOH 



H\/\/H m\/\xo 



H KB H NH 



Tryptophan Thyroxin 



The fate of the amino acids in the body may be summarized in the 

 following table : 



TABLE III 

 FATE OF AMINO ACIDS IN THE ANIMAL BODY 



Ammo-acid 



Gives Rise to Glucose 



Gives Rise to Acetone 

 Bodies 



Glycocoll 



Alanin , 



Valin 



Leucin 



Isoleucin 



Normal Leucin 



Aspartic Acid 



Glutamic Acid 



t-hydroxyglutamic Acid 

 erin 



Cystin 



Lysin 



Arginin (Ornithin) .... 



Phenylalanin 



lyrosin 



Prolin 



Oxyprolin 



Histidin 



Tryptophan 



+ 

 + 

 + 

 + 



+ 



Ten of the amino-acids are known definitely to give rise to glucose, and it 

 is very possible that the four marked with the query may also give rise to 

 glucose. 



It was found by Lusk that dogs rendered diabetic by means of phlo- 

 rhizin excrete 3.6 grams of glucose for every 6.25 grams of protein that 

 they catabolize. Lusk and Mandel showed that severe human diabetics 

 may excrete sugar in the same proportion, which means that from every 

 one hundred grams of proteins catabolized, fifty-nine grams of sugar 

 can be formed. 



This does not yet complete the tale for three of the amino-acids give 

 rise to not inconsiderable quantities of acetone bodies. Glucose and 

 P-hydroxy butyric acid seem therefore to be the two important stations along 



