THE CHEMICAL CONSTITUTION OF ITS UNITS 53 



Glutamic Acid. 



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

 by Ritthausen in 1 866, who obtained it from wheat gluten by hydrolysis 

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

 it glutaminic 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 

 oxy-acid, 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 Markownikoff to 

 be what we now call glutaric acid ; this was identical with the sub- 

 stance obtained by the hydrolysis of trimethylene cyanide, which was 

 prepared from trimethylene bromide CH 2 Br. CH 2 . CH 2 Br and potas- 

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

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

 acid, 



COOH COOH 



CHOH CH\ 



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

 the 7-lactone. i 2 O 



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

 for this constitution was only given in 1 890 by L. Wolff who synthesised 

 glutamic acid from laevulinic acid. Dibromolaevulinic acid is obtained 

 by bromination, and this when boiled with water gives diacetyl and 

 glyoxylpropionic acid ; diisonitrosovalerianic acid is formed from the 

 latter, on treatment with hydroxylamine : 



