ii PRIMARY DISSOCIATION-PRODUCTS 49 



25. Tyrosin, C 9 H n N0 3 



HO<^>CH 2 . CH(NH 2 ) . COOH 



is phenyl-/?-hydroxy-a-amino-propionic acid. It was one of the first dis- 

 covered dissociation-products, and was estimated quantitatively at an 

 early period because of its slight solubility. Even now the best 

 method of estimating it consists in freeing the mixture of dissociation- 

 products from sulphuric acid, barium hydrate, or hydrochloric acid, 

 and then inspissating the remainder, when tyrosin crystallises out 

 fairly completely and approximately pure (for its separation from 

 leucin, see p. 23). In contrast to phenylalanin, it is characteristic 

 of the hemi-group of the albumin molecule, 1 and is therefore absent in 

 gelatine and in hetero-albumose, also in some protamins. 



The occurrence of tyrosin in plants has been definitely established 

 by Sack and Tollens, 2 who found it in the berries of the elder 

 (Sainbucus nigra, L.); by Steudel, 3 and by Schulze and Winterstein, 4 

 who discovered it in potatoes and in germinating cucumber. 



The naturally occurring variety is Z-ty rosin. 5 E. Fischer 5 found 

 for a solution of tyrosin in 21 per cent hydrochloric acid 



a D = -8-64. 



Schulze and Winterstein discovered, however, that tyrosin differs 

 from other amino-acids in showing the greatest amount of rotation 

 in 4 per cent hydrochloric acid, for which strength 



a D = - 14-6 to 16'1. 



By splitting racemic tyrosin into its optically L active components E. 

 Fischer obtained in 4 per cent HC1 



while Schulze and Winterstein have prepared from germinating lupine 

 a tyrosin having 



a = - 16'2. 



D 



1 W. Kiihne, Verh. d. Heidelberger naturhist. med. Vereins, N.F. III. 286 (1885) ; 

 W. Kiihne and R. H. Chittenden, Zeitschr. f. Biologic, 22. 423 (1886) ; E. P. Pick, 

 Zeitschr. f. physiol. Ghem. 28. 219 (1895) ; E. Fischer and P. Bergell, Chemikerzeitung, 

 1902, II. p. 939 ; E. Fischer and E. Abderhaldeu, Zeitschr. f. physiol. Chem. 39. 81 

 (1903). 



2 J. Sack, Dissertation, Gottingen, 1901 ; and J. Sack and B. Tollens, Ber. d. deutsch. 

 chem. Ges. 37. 4115 (1904). 



3 H. Steudel, Deutsche med. Wochenschr. 1900, p. 273. 



4 E. Schulze and E. Winterstein, Zeitschr. /. physiol. Chem. 35. 299 (1902), and 

 45. 79 (1905). 



5 E. Fischer, Ber. d. deutsch. chem. Ges. 32. III. 3638 (1899). 



E 



