4 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



The Condensation Together of Amino Acids. 



The earliest investigations upon the condensation together of amino 

 acids were made by Schaal in 1871, who heated asparagine hydro- 

 chloride in a current of carbonic acid for three days at 180 C., whereby 

 he obtained a hard white mass, the greater portion of which was insol- 

 uble in water and the remainder solubte only with difficulty. The 

 insoluble body was formed by the loss of fifteen molecules of water 

 from eight molecules of aspartic acid, and the other body by the loss 

 of seven molecules of water from four molecules of aspartic acid : 



C 16 H 14 N 4 9 = 4 C 4 H 7 N0 4 - 7 H 2 

 C 32 H 26 N 8 17 = 8C 4 H 7 N0 4 - i 5 H 2 O 



Both compounds were converted into aspartic acid by hydrolysis 

 with baryta water. 



; J. Guareschi, in 1 876, further investigated these substances by 

 determining the amount of silver in the silver salts, but their nature 

 was only demonstrated in 1897-1899 by Schiff. He obtained them by 

 heating aspartic acid, prepared from asparagine and dried at 110 C., 

 for twenty hours at 190-200 C., the yield amounting to 72-75 per cent. 

 Not only were the anhydrides, octaspartide and tetraspartide, as Schiff 

 called these compounds, formed in the process, but also the tetraspartic 

 and octaspartic acids. These acids he also prepared from the anhydrides 

 by hydrolysis with the calculated quantity of cold dilute alkali. From 

 the analysis of their salts, as also their anilides and phenylhydrazides, 

 and from the fact that they gave the biuret reaction which was not 

 observed by Schaal, but pointed out by Grimaux in 1882, he gave these 

 acids the following formulae: 



CO CO 



C.NH 2 ^C. 



CH 2 CH 



COOH COOH 



Tetraspartic acid 



CO CO CO CO CO CO CO COOH 

 H.C.NH 2 C.NH 2 C.NH 2 C.NH 2 C.NH" 2 C.NH 2 C. NH 2 C.NH 2 

 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 



COOH COOH COOH COOH COOH COOH COOH COOH 



Octaspartic acid 



and their anhydrides : 



