THE CHEMICAL CONSTITUTION OF ITS UNITS 55 



Cl . CH 2 . CH 2 . COOC 2 H 5 . In view of our having only one synthesis 

 of each of these two amino acids, and these syntheses being somewhat 

 arduous, Sorensen's suggestion might with advantage be carried out. 



C. DlAMINOMONOCARBOXYLIC ACIDS. 



Drechsel's discovery of lysine amongst the products of hydrolysis of 

 caseinogen in 1889 first showed that the monoamino acids were not the 

 only constituents of the protein molecule ; the substance, lysatinine, which 

 he and his pupils also isolated a few years later from several proteins, 

 was shown by Hedin to be a mixture of arginine and lysine, the former 

 body having been many years previously obtained by E. Schulze and 

 E. Steiger from germinating seedlings. Though ornithine had been 

 discovered over ten years before lysine, its importance as a constituent 

 of the protein molecule was not recognised until it was shown by 

 Schulze to be a constituent of arginine. Histidine, discovered in 1896 

 by Kossel, was classed with the diamino acids until its constitution was 

 determined, on account of its method of separation and its close rela- 

 tionship in many of its properties to arginine and lysine, the three 

 bases having been termed by Kossel as the hexone bases and regarded 

 as a very important portion of the protein molecule. 



The synthesis of the diamino acids, in comparison with that of the 

 monoamino acids, is very much more difficult and has only been 

 achieved within the last few years. 



Diamino -acetic Acid. This acid, the first member of the series, was 

 described by Drechsel as a decomposition product of caseinogen. Its 

 existence is extremely doubtful, its attempted synthesis by Klebs did 

 not succeed, and Willstatter could only obtain certain of its derivatives. 



Diaminopropionic Acid has not yet been described as a constituent 

 of the proteins, but it was synthesised by Klebs in 1894 by the action 

 of ammonia upon dibromopropionic acid. 



Diaminobutyric Acid. a-7-Diaminobutyric acid was prepared in 

 1901 by E. Fischer by the same method as he employed in the synthe- 

 sis of ornithine. 



Ornithine or a, -diaminovalerianic Acid. In 1877 Jaffe obtained 

 from the urine of birds, which he had fed with benzoic acid, dibenzoyl 

 ornithine or ornithuric acid, and from this substance he prepared orni- 

 thine chloride. He regarded it as a diaminovalerianic acid, the first 

 known representative of the series of diamino acids, but only in 1898 

 was the position of the two amino groups definitely determined by 

 Ellinger, who obtained putrescine from it by putrefaction ; the identity 

 ofputrescinewith tetramethylenediamine had been previously shown by 



