16 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Anhydrides with Urea, etc. The researches of Schiitzenberger be- 

 tween 1875 and 1880 upon the products of hydrolysis of proteins by 

 the action of baryta water under pressure, led the French chemists to 

 the belief that the proteins were composed of amino acids and urea or 

 oxamide. In 1882 therefore Grimaux heated Schaal's aspartic acid 

 anhydride with urea for two hours at 125-130 C. A thick mass 

 almost entirely soluble in water resulted ; its solution was gelatinous 

 and difficult to filter, and it possessed the properties of colloidal sub- 

 stances, behaving very like albumin. This polyaspartic ureide gave 

 the biuret reaction, and was converted by baryta into carbonic acid, 

 ammonia and aspartic acid ; it had the formula C 34 H 40 N 10 O 26 , and con- 

 sisted of eight molecules of aspartic acid and two molecules of urea. 

 Schiff gave it the formula : 



COOH 



I x / I ^\ 

 HN 



CO CH, 



I 

 HN-CO \ COOH/ 



In 1888 Schiitzenberger, who regarded proteins to be composed of 

 (i) urea and oxamide; (2) leucines, or amino acids of the formula 

 CnHm + iNO 2 , where n = 6, 5, 4, 3, 2 ; (3) leuceines, or amino acids 

 of the formula C n H 2n - 1 NO 2 , where n = 4, 5, 6, and that there was 

 one molecule of leucine to one molecule of leuceine, prepared the leu- 

 ceines by the action of ethylene dibromide upon the zinc salts of the 

 lower leucines, such as glycine and alanine, according to the equations 

 C,H,NO 9 + C 8 H 4 Br, = aHBr + C 4 H 7 NO, 

 C 3 H 7 NO a + C a H 4 Br, = 2HBr +C e H 9 NO, 



and in 1891 he heated a mixture of leucine and leuceine with 10 per 

 cent, of urea, carefully dried at 1 10 C., with phosphoric anhydride. He 

 obtained a mass soluble in water, which was precipitated by several 

 volumes of alcohol ; it gave the biuret reaction and other protein 

 reactions, and Schiitzenberger regarded it as a " pseudo-peptone 

 synthetique ". 



