THE PROTEINS 13 



Pecten irradians Chittenden found glycocoll in a free state; 

 and it has been reported as occurring in the urine under vari- 

 ous pathological conditions. After administration of benzoic 

 acid to man and animals hippuric acid (benzoyl-glycocoll) is 

 found in the urine thus demonstrating a synthesis of hip- 

 puric acid from benzoic acid and glycocoll. J> 



Alanine a-amino-propionic acid. CHa.CH < 

 was prepared synthetically previous to its isolation 

 from among the protein decomposition products and was 

 named by its discoverer, Strecher. Alanine has been shown 

 to be a constant decomposition product of proteins. 



Valine a.-amino-isovalerianic acid. >CH.CH< 



In 1856 v. Gorup-Besanez isolated a substance having the 

 formula CsHnNC^ from pancreas and because it possessed 

 properties similar to leucine he looked upon it as a homologue 

 of leucine and called it butalanine. Although a similar sub- 

 stance was isolated from certain seedlings by Schulze and 

 Barbieri, and from the protamine, clupeine, by Kossel, it was 

 not until 1906 that its identity was established by Fischer 

 who gave it the name of valine. Valine is obtained from most 

 proteins. 



Leucine. a-amino-isobutylacetic acid. 



CH SCH CH CH^ NHi 

 CH3> <COOH 



Leucine was described by Proust in 1818 and was called 

 oxide-caseux. Braconnot in 1820 obtained a substance from a 

 hydrolysis of meat which on account of its glistening white 

 appearance he called leucine. Liebig regarded it as one of the 

 constituents of the protein molecule and this was later proved 

 to be correct. Leucine is also a constituent of many organs 

 and tissues occurring in the free state. It is yielded by both 



