CH. IV.l TYROSINE. 95 



reddish-violet colour is produced, which turns yellow on adding an 

 excess of bromine. If the addition of the bromine water be stopped 

 when the red colour has reached its maximum intensity, it will be 

 found that the coloured product can be shaken out with a few cc. of 

 amyl or butyl alcohol. 



B. To a small knife point of tryptophane add a few cc. of 

 41 reduced oxalic acid " (see Ex. 23). Add an equal volume of pure 

 sulphuric acid and mix. A beautiful purple colour is produced. 



C. To a small knife point of tryptophane add about I cc. of 

 water, 2 drops of a 5 per cent, solution of cane sugar, and 5 cc. of pure 

 hydrochloric acid. Boil for about a minute. A deep purple solution 

 is obtained. 



D. Dissolve about 0-05 gram, of tryptophane in 5 to 10 cc. of 

 water by boiling in a test tube. Add as much freshly prepared, 

 washed copper hydroxide (see note to Ex. 79) as will go on a large 

 spatula and boil for i minute. Filter hot. The nitrate is not blue 

 and gives no reactions for tryptophane. The precipitate contains 

 the copper salt of tryptophane, which is characteristically insoluble 

 except in the presence of even traces of other amino-acids. It is 

 then soluble in their copper salts. 



Tyrosine. 



Tyrosine is the least soluble of the amino-acids', and for 

 that reason is easily obtained from proteins. When casein 

 is digested by trypsin, under the conditions described in 

 Ex. 87, it generally happens that a considerable amount 

 separates as a chalky white precipitate in 6 to 10 days. 

 The amount separating varies with the activity of the 

 ferment preparation, and on the particular sample of casein 

 employed. If a good yield of tyrosine is especially desired 

 it is advisable to concentrate the filtrate obtained in 

 Ex. 87, B (i.) to about one-fourth, allow to cool over-night, 

 filter off the precipitate on the pump, and purify by the 

 method described below. The concentrated filtrate can be 

 diluted, and used for the isolation of tryptophane, but 

 owing to its unstability, the yield of this latter amino- 

 acid is very apt to be poor. 



