TYROSINE. 153 



Naturally occurring tyrosine and that obtained by the cleavage of 

 protein substances by acids or enzymes, is generally Z-tyrosine, while 

 that obtained by decomposition with baryta-water or prepared syn- 

 thetically is inactive, v. LIPPMANN l has obtained d-tyrosine from 

 beet-sprouts. The statements as to specific rotation of tyrosine are 

 somewhat variable. For tyrosine from proteins E. FISCHER has found 

 a rotation of (C*)D = ~ 12.56 to 13.2 for the hydrochloric acid solution, 

 while SCHULZE and WINTERSTEIN 2 obtained higher results using tyrosine 

 from plants, namely, (a) D = 16.2. 



Tyrosine in a very impure state occurs in the form of balls similar 

 to leucine. The purified tyrosine, on the contrary, appears as colorless, 

 silky, fine needles which are often grouped into tufts or balls. It is diffi- 

 cultly soluble in water, being dissolved by 2454 parts of water at 20 C, 

 and 154 parts boiling water, separating, however, as tufts of needles on 

 cooling. It dissolves more easily in the presence of alkalies, ammonia, 

 or a mineral acid. It is difficultly soluble in acetic acid. Crystals of 

 tyrosine separate from an ammoniacal solution on the spontaneous 

 evaporation of the ammonia. One hundred parts glacial acetic acid 

 dissolve on boiling only 0.18 part tyrosine, and by this means, especially 

 on adding an equal volume of alcohol before boiling, the leucine can be 

 quantitatively separated from the tyrosine (HABERM ANN and EHREN- 

 FELD 3 ) . The Z-tyrosine-ethyl-ester crystallizes in colorless prisms which 

 melt at 108-109 C. The naphthylisocyanate-Z-tyrosine melts at 205- 

 206. Tyrosine can be oxidized with the formation of dark-colored 

 products by various plant as well as animal oxidases, so-called tyro- 

 sinases (see Chapters XV and XVI). In alcoholic fermentation of sugar 

 the tyrosine present at the same time is transformed according to F. 

 EnRLiCH 4 into tyrosol (p-oxyphenylethyl alcohol), CgHioC^. Tyrosin is 

 identified by its crystalline form and by the following reactions: 



PIRIA'S Test. Tyrosine is dissolved in concentrated sulphuric acid 

 by the aid of heat, by which tyrosine-sulphuric acid is formed; it is 

 allowed to cool, diluted with water, neutralized by BaCOa, and filtered. 

 On the addition of a solution of ferric chloride the filtrate gives a beautiful 

 violet color. This reaction is disturbed by the presence of free mineral 

 acids and by the addition of too much ferric chloride. 



HOFMANN'S Test. If some water is poured on a small quantity of 

 tyrosine in a test-tube and a few drops of MILLON'S reagent added and 



1 Ber. d. d. chem. Gesellsch., 17. 



2 See Hoppe-Sey ler-Thierf elder, Handb. d. physiol. u. pathol. chem. Analyse, 8. 

 Aufl., 1909. Also E. Fischer, Ber. d. d. chem. Gesellsch., 32; Schulze and Winter- 

 stein, Zeitschr. f. physiol. Chem., 45. 



3 Zeitschr. f. physiol. Chem., 37. 



4 Ber. d. d. chem. Gesellsch., 44. 



