190 



TYROSIK 



is however some conflict of opinion as to its constancy in such cases. 

 It is also present in not inconsiderable quantities, along with leucin, 

 in many plant tissues. 



Tyrosin crystallises in exceedingly fine needles which are usu- 

 ally collected into feathery masses. The crystals are snow- 

 white, tasteless, and odourless. If crystallised from an alkaline 

 solution tyrosin often assumes the form of rosettes composed of 

 fine needles arranged radiately. 



The crystals are very sparingly soluble in cold water (1 in 

 2000 at 20), much more soluble in boiling water (1 in 150) ; 



FIG. 32. TTROSIN CRYSTALS. (Krukenberg.) 



they are almost insoluble in strong alcohol (1 in 13500) and 

 quite insoluble in ether. They are readily soluble in acids and 

 particularly so in ammonia and other alkalis and in solutions of 

 alkaline salts. 



Preparation, (i) The products of a prolonged pancreatic diges- 

 tion of proteids are neutralised and filtered ; the filtrate when 

 concentrated usually yields crusts of tyrosin crystals, which may 

 be readily purified by solution in a little boiling water from 

 which they separate out on cooling after concentration if neces- 

 sary, (ii) Horn shavings are boiled for 24 hours with sulphuric 

 acid (5 of acid to 13 of water). The sulphuric acid is then sepa- 

 rated by the addition of lime, and the filtrate from the calcium 

 sulphate yields as before crusts of tyrosin crystals on concentra- 

 tion and cooling. These are then purified by recrystallisation 

 from boiling water. 1 Any leucin at first present in the crystal- 



1 These methods suffice for the preparation of small amounts of tyrosin for 

 purposes of study. For full details of its preparation and most productive 

 separation from leucin see Hlasiwetz and Habermann, quoted sub leucin. See 

 also E. Schulze, Zt. f. physiol. Chem. Bd. ix. 1885, Sn. 63, 253, on the separation 

 of amido-acids. 



