1 14 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Schmidt and Widmann have prepared the ester of aspartic acid 

 from acetyl-succinic ester. This was converted by the action of nitrous 

 acid into the nitroso-derivative, which, on reduction with zinc and 

 acetic acid, gave aspartic ester : 



COOC 2 H 5 COOC 2 H 5 COOC 2 H 5 



CH.CO.CH 3 CH.NO CH . NH 2 



! -> I -* J 



CH 2 CH 2 CH 2 



COOC 2 H 5 COOC 2 H 5 COOC 2 H 5 . 



Glutamic Acid. 



The presence of this amino acid in the protein molecule was shown 

 by Ritthausen in 1866, who obtained it from wheat gluten by hydrolysis 

 with sulphuric acid. He showed that it was an amino acid and termed 

 it glutamic acid, on account of its first preparation from gluten. 

 Subsequently Ritthausen and Kreussler isolated it from the hydrolysis 

 products of other vegetable proteins. Kreussler could not demonstrate 

 its presence in animal proteins, in which it was afterwards shown to 

 occur in 1873 by Hlasiwetz and Habermann. Not only is glutamic 

 acid formed by acid hydrolysis, but also by the action of enzymes : 

 Knieriem and Kutscher obtained it by the tryptic digestion of fibrin, and 

 its amide, glutamine, is found in the extracts of seedlings, as shown by 

 Schulze, v. Gorup-Besanez and Scheibler. 



Ritthausen gave glutamic acid the empirical formula C 5 H 9 NO 4 , and 

 found that, when treated with nitrous acid, it was converted into an 

 oxyacid, which he termed glutanic acid and regarded as a homologue 

 of malic acid. Dittmar again prepared glutanic acid and reduced it with 

 hydriodic acid to an acid which was shown by Markownikoffto be what 

 we now call glutaric acid ; this was identical with the substance ob- 

 tained by the hydrolysis of trimethylene cyanide, which was prepared 

 from .trimethylene bromide CH 2 Br . CH 2 . CH 2 Br and potassium 

 cyanide. Glutanic acid differed from Simpson's /3-hydroxy-glutaric 

 acid, and Markownikoff regarded it as the a-hydroxy-glutaric acid, 



COOH COOH 



CHOH CH^ 



I which, according to Bredt, exists in the free state as I \ 



CH 2 Lria \~ 



the 7-lactone. I 



CH 2 CH 2 / 



COOH CO ' 



Glutamic acid would therefore be a-aminoglutaric acid. The proof 



