84 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



completely dissolves. A flocculent precipitate gradually separates 

 from the solution and is removed by filtration. The solution is again 

 evaporated in vacuo, and the residue is dissolved in about 200 c.c of 

 water warmed to 60 C., the more insoluble portions being removed by 

 filtration. To a test portion absolute alcohol is added until there is a 

 distinct turbidity and to the remainder the corresponding volume re- 

 quired is added. On scratching the sides of the vessel and seeding the 

 solution with a crystal of d-alanyl-glycine the compound crystallises 

 out in about twenty-four hours. It is filtered off, washed with alcohol 

 and ether, dissolved in water and again precipitated by absolute alcohol. 

 The yield amounts to about 8 per cent 



The study of silk which has been undertaken by Abderhalden has 

 shown that the different varieties contain different amounts of amino 

 acids. They seem also to yield different anhydrides on partial 

 hydrolysis : 



Canton silk yielded glycyl-d-alanine anhydride and glycyl-1-tyrosine 

 anhydride. Chwang silk and Indian Tussore silk yielded d-alanine 

 anhydride and glycyl-d-alanine anhydride. From both Canton silk 

 and Bengal silk d-alanyl-glycine has been isolated by the above 

 method. 



In the case of tripeptides where six isomers are possible the de- 

 termination of the constitution was again attempted by Abderhalden 

 and Funk by the conjugation of the compound with naphthalene-sulph- 

 onyl-chloride. This radicle becomes attached to the amino acid at 

 the beginning of the chain ; on hydrolysis the amino acids are separated 

 but the naphthalene-sulphonyl radicle remains attached ; the isolation 

 of this derivative shows which amino acid is in combination and stood 

 originally at the beginning of the chain. For example : 



Alanyl-glycyl-tyrosine will yield naphthalene-sulphonyl-alanyl- 

 glycyl-tyrosine which on hydrolysis will give naphthalene-sulphonyl- 

 alanine, glycine and tyrosine. In this particular example, however, 

 the OH group of tyrosine also reacts with the naphthalene-sulphonyl- 

 chloride, and mono-naphthalene-sulphonyl-tyrosine will be obtained 

 instead of tyrosine. If tyrosine stands at the commencement of the 

 chain the product is di-naphthalene-sulphonyl-tyrosine. 



The treatment of a peptone-like product from silk with this reagent 

 and subsequent hydrolysis gave naphthalene-sulphonyl-alanine, mono- 

 naphthalene-sulphonyl-tyrosine and glycine, from which it was concluded 

 that alanine was at the commencement, glycine in the centre, and 

 tyrosine at the end, *>., that the compound was alanyl-glycyl-tyrosine. 



