SERINE. 143 



recently it has been found by others l among the products of hydrolysis 

 of the proteins. It seems to be associated regularly with ordinary 

 leucine, forming mixed crystals, which give an impression of a chemical 

 combination and which are difficult to separate. On this account the 

 earlier claims as to the quantity of leucine are somewhat uncertain, as 

 they always refer to leucine containing isoleucine. 



The constitution of isoleucine has been explained by EHRLICH through 

 its relation to d-amyl alcohol. In the fermentation of sugar by 

 yeast it yields d-amyl alcohol, and on the other hand, it can also be 

 obtained, in a manner analogous to the synthesis of leucine, from 

 c?-amyl alcohol (as a mixture of isoleucine and alloisoleucine, the latter 

 is levogyrate and has a different stereometric configuration from the 

 isoleucine). The synthesis of isoleucine has been accomplished in 

 other ways by EHRLICH, by BRASCH and FRIEDMANN and by BOUVEAULT 

 and LocQinx. 2 



Isoleucine crystallizes in leaves or rods and plates of the rhombic 

 form. It is more soluble in water than leucine (1:25.8). Its solutions 

 have a bitter taste and are astringent. It is dextro-rotatory in aqueous 

 as well as in acid solution. In aqueous solution it has a specific rotation 

 of (a) D =+9.74 and in 20-per cent hydrochloric acid (a) D =+36.8. 

 Like valine its copper salt is readily soluble in methyl alcohol. The 

 benzoyl combination melts at 116-117, the benzene sulphoisoleucine 

 at 149-150, the phenylisocyanate combination at 119-120, and the 

 naphthylisocyanate combination at 178 C. 



CH 2 (OH) 



Serine (a-amino-/?-oxypropionic acid) C 3 H7NO3 = CH(NH 2 ), was 



COOH 



obtained by FISCHER and his collaborators as a cleavage product of 

 several proteins, generally only in small quantities. The largest quan- 

 tity, 6.6 per cent, was obtained by FISCHER and SKITA S from sericine; 

 KOSSEL and DAKIN 4 obtained a still larger amount from salmine, namely 

 7.8 per cent. The racemic serine is the one generally obtained. From 

 fibroin FISCHER 5 obtained a mixture of active and inactive serine anhy- 

 dride from which he finally prepared Z-serine by hydrolysis. 



Synthetically d-Z-serine has been prepared by FISCHER and LEUCHS 



1 Felix Ehrlich, Ber. d. d. chem. Gesellsch., 37; Winterstein ami Pantanelli, Zeitschr. 

 f. physiol. Chem., 45. 



2 Ehrlich, Ber. d. d. chem. Gesellsch., 40 and 41; Brasch and Friedmann, Hof- 

 meister's Beitrage, 11; Bouveault and Locquin, Compt. rend., 141, and Bull. soc. 

 chim. (3), 35; Locquin, Bull. soc. chim. (4), 1. 



3 Zeitschr. f . physiol. Chem., 35. 



4 Fischer and Skita, Zeitschr. f. physiol. Chem., 35; Kossel and Dakin, ibid., 41. 



5 Ber. d. d. chem. Gesellsch., 40. 



