ISOLATION AND ESTIMATION OF TYROSINE 19 



The data for tyrosine by the gravimetric method by various workers 

 are in some cases quite concordant, but there are instances in which 

 the data are very different, e.g., Abderhalden and Langstein [1910] give 

 4 -6 per cent, for the amount of tyrosine in caseinogen, whereas Osborne 

 and Guest [1911] were only able to isolate 3-4 per cent. The same 

 quantity was obtained by Totani [1916]. Totani was able to isolate 

 up to 4 -I per cent, by the further treatment of the liquid with 

 mercuric sulphate. Osborne and Clapp [1907, 8] have emphasised the 

 fact that from zein it is extremely difficult to crystallise the whole of 

 the tyrosine, and Abderhalden and Fuchs [1913] also make a similar 

 statement. They state further that better yields are obtained by 

 evaporating the solutions in vacua, which prevents access of acid and 

 alkali vapour which keeps the tyrosine in solution and prevents it from 

 crystallising. Sometimes the basic di-amino acids such as lysine form 

 a combination with tyrosine preventing crystallisation. It may be 

 generally considered that all these data are minimal. 



In order to obtain tyrosine E. K. Marshall, jun. [1913], pointed out 

 that it was made more quickly and with less manipulation if it were 

 prepared by the tryptic digestion of caseinogen. Pig's pancreas was 

 finely minced, mixed with an equal weight of water, and allowed to 

 stand in the presence of chloroform for two days, whereupon the mix- 

 ture was incubated at 37 for twenty-four hours, cooled and filtered. 

 100-150 grams of caseinogen are added per litre of filtrate, the solu- 

 tion is made slightly alkaline with ammonia and digested at 37 for 

 three to seven days. Tyrosine separates out and is filtered off after 

 cooling. The solid matter is extracted with 1000, 500, and 250 

 c.c. of boiling water and these extracts are evaporated to 250 c.c. 

 The tyrosine which crystallises out is obtained quite pure by one re- 

 crystallisation. The yield is given as 5 grams from 100 grams of 

 caseinogen and I -2 grams from I litre of pancreas extract. 



This method of preparation of tyrosine has been used for many 

 years by the author by digesting caseinogen dissolved in alkali with 

 various preparations of trypsin. The yields were never so high as the 

 3 -8 per cent, obtained by Marshall ; on the average about 2-5 per cent. 



