ISOLATION OF GLUTAMIC ACID 33 



THE OTHER MONO-AMINO ACIDS. 



The isolation and estimation of these units is usually not carried 

 out separately, except occasionally for glutamic acid and glycine. 

 The process is one which yields the mono-amino acids in sequence. 



The method generally adopted in isolating the other mono-amino 

 acids is that first employed by E. Fischer [1901]. It has been modi- 

 fied in certain details by his pupils, particularly Abderhalden [1910] 

 and other workers have contributed to its improvement. 



Hydrolysis is more conveniently effected by concentrated hydro- 

 chloric acid than by dilute sulphuric acid, and is carried out as 

 mentioned on p. 9. 



(i) Isolation of Glutamic Acid as Hydrochloride. 



The method of isolation of glutamic acid as hydrochloride was 

 introduced by Hlasiwetz and Habermann [1873]. 



The solution of amino acids in 25 per cent, hydrochloric acid is 

 concentrated in vacua to a half or a third of the original volume, and 

 glutamic acid, if present in any large amount, is removed as its hydro- 

 chloride by saturating the solution with dry gaseous hydrochloric acid. 

 After allowing to stand at o for some days, glutamic acid hydro- 

 chloride crystallises out. This occurs in the case of caseinogen and 

 certain vegetable proteins, which contain from 10-40 per cent, of this 

 amino acid. The glutamic acid hydrochloride is filtered off after add- 

 ing an equal volume of ice-cold alcohol, washed with alcoholic hydro- 

 chloric acid, redissolved in water, and boiled with baryta to remove 

 ammonia. The barium is removed with sulphuric acid and the gluta- 

 mic acid is again precipitated as hydrochloride by saturating the 

 solution with gaseous hydrogen chloride. It is usually quite pure. 

 The mother liquor on further concentration may give further crops of 

 glutamic acid hydrochloride. These are treated in the same way as 

 the first crop. The whole of the glutamic acid in the protein is not 

 always precipitated as hydrochloride ; the remainder is then isolated 

 later. The precipitation of glutamic acid hydrochloride is, however, so 

 nearly complete that the yield is considered quantitative. Many com- 

 parative determinations of the glutamic acid content of various pro- 

 teins have been made by Abderhalden and his co-workers, and a series 

 of values in numerous vegetable proteins and a few animal proteins 

 have been published by Osborne and Gilbert [1906]. Abderhalden 

 PT. i. 3 



