AMINO ACIDS 449 



of glycyl-leucine from elastin. Levene and Beatty * also 

 claim to have obtained prolyl-glycine from the hydrolysis of 

 gelatine. 



Abderhaldenf also mentions certain substances of a poly- 

 peptide nature which he found amongst the products of pan- 

 creatic digestion of a number of proteins such as casein, 

 edestin, haemoglobin, serum globulin, egg albumin and 

 fibroin. 



A polypeptide of considerable importance is that known as 

 Glutathione ; this substance, whose constitution has been 

 established by synthesis, $ has the formula — 



CH2— SH ^SH— CH2 



CH . NH . CO . CH2 CH., . CHNH2 . COOH CH . NH . CO . CH., . CH^ . CHNH^ COOH 



I I 



COOH COOH 



and is thus a diglutaminyl cystine. The significance of this 

 substance as an oxidizing mechanism is discussed in Vol. II. 



OCCURRENCE OF AMINO ACIDS IN PLANTS. 



Leucine occurs as such in the buds of the horse-chestnut § 

 and many other plants. Isoleucine has been discovered by 

 Felix Ehrlich || in the residual molasses obtained from sugar 

 refineries. 



Lysine and histidine have been isolated from sprouting 

 plants by Schulze.^ 



Arginine has been observed in the cotyledons of lupin 

 seeds and in etiolated pumpkin seeds,** and also in several 

 species of conifers. 



Phenylalanine was discovered by Schulze and Barbieri ft 

 in etiolated germinating lupin seeds. 



* Levene and Beatty : " Ber. deut. chem. Gesells.," 1906, 39, 2060. 



t Abderhalden : " Zeit. physiol. Chem.," 1905, 44, 28, 33. 



X Stewart and Tunnicliffe : " Biochem. Journ.," 1925, 19, 207. 



§ Schulze and Barbieri : " J. prakt. Chem.," 1882, 15, 145. Schulze 

 and Winterstein : " Zeit. physiol. Chem.," 1902, 35, 299. 



!l Ehrlich : " Ber. deut. chem. Gesells.," 1904, 37, 1809. 



^ Schulze : " Zeit. physiol. Chem.," 1899, 28, 465. 



** Schulze and Steiger : id., 1887, 1 1, 43 ; " Ber. deut. chem. Gesells.," 

 1886, 19, 1177. 



tt Schulze and Barbieri: id., 1881, 14, 1785. 



29 



