CHEMICAL COMPOSITION OF PROTEIN MOLECULE n 



The next operation consists in the reconversion of the esters into the 

 amino acids. In the case of the lower boiling fractions, this recon- 

 version is effected by boiling the esters with five to six volumes of 

 water under a reflux condenser for six to seven hours, until the alkaline 

 reaction has disappeared ; in the case of the higher boiling fractions, 

 which contain the esters of aspartic and glutamic acids, the reconversion 

 is effected by boiling with baryta water for one and a half to two hours ; 

 hydrolysis by water alone only converts these esters into their acid 

 esters. Phenylalanine ester is converted into its hydrochloride by eva- 

 poration to dryness with hydrochloric acid. 



The Separation and Characterisation of the Individual Monoamino 



Acids. 



The separation, estimation and characterisation of each constituent 

 contained in an ester fraction has still to be carried out after the con- 

 version into the free amino acid, and for each amino acid a somewhat 

 special process has to be performed, which is best described for each 

 individual product. 



Glycine. As previously stated, if glycine occurs in large amounts in 

 a protein, the greater quantity of it is separated as ester hydrochloride 

 before the esters are liberated from their hydrochlorides and fractionally 

 distilled. The remainder is contained in the first ester fraction, from 

 which it is obtained by again esterifying and separating as ester hydro- 

 chloride. It is identified by its melting point and by elementary 

 analysis, and its amount determined by its yield. 



Alanine. After the glycine has been removed as -above described, 

 the alanine is obtained by crystallisation after removal of the hydro- 

 chloric acid by boiling with lead hydroxide. 



When mixed with valine, leucine and proline, the two former separate 

 in the first fractions on crystallisation when their solution is evaporated ; 

 if present in large amounts it crystallises out in an almost pure state. 

 It is separated from proline by evaporating to dryness and boiling with 



