6 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



5. Diaminotrioxydodecanic acid, C 12 H 26 O 5 N 2 , was isolated by 

 Fischer and Abderhalden [1904] from some tyrosine prepared from 

 caseinogen. Other workers have subsequently searched for this com- 

 pound, but have never isolated it. Abderhalden and Weil [1912, 2] 

 stated that it had been obtained in very varying yields, which made it 

 appear probable that it was a secondary product of hydrolysis and that 

 its constitution appeared to be different to that implied by its name. 



6. A substance of the formula C U H 15 O 5 N was isolated by Torquati 

 [1913, I, 2] from the seedlings and green pods of the vetch, ViciaFaba. 

 This compound was investigated by Guggenheim [1913], who ascer- 

 tained that its elementary composition corresponded more closely to 

 the formula C 9 H U O 4 N, and that its constitution was 3, 4, dihydroxy- 

 phenylalanine, 



OH 



CH 2 . CH(NH 2 ) . COOH 



In properties it resembled the synthetical dl-dihydroxyphenylalanine 

 described by Funk [1911] and also by Stephen and Weizmann [1914]. 

 Like adrenaline this substance possesses a pyrocatechin nucleus. (See 

 Barger's Simpler Natural Bases.} 



7. Gortner [1911] mentions the presence in wool of an aromatic 

 phenolic compound, which gives Millon's reaction but is not tyrosine. 

 If it should prove to be dihydroxyphenylalanine, this compound may 

 prove also to be present in other proteins and to be a unit of general 

 occurrence. 



8. Abderhalden and Kempe [1907, i], in preparing tryptophan by 

 the tryptic digestion of caseinogen, observed the presence of another 

 compound of the formula C n H 12 N 2 O 3 . It was found more frequently 

 when the digestion was prolonged and the subsequent preparation was 

 slow ; it seems to be an oxidation product of tryptophan. It does not 

 give the usual reactions for tryptophan and is converted by hydrochloric 

 acid into a quinoline derivative. It is known as oxy tryptophan. 



9. 3, %-Diiodotyrosine is present in the protein contained in corals 

 and other sea animals : it is formed when proteins are treated with the 

 halogen : it is not included in the above list since it is of such rare 

 occurrence and presumably a derivative of tyrosine. 



10. Glucosamine. The presence of glucosamine in the protein 

 molecule is a disputed question ; there is no doubt that a carbohydrate 



