POLYPEPTIDES 71 



Applications. 



The synthetical polypeptides have been made use of by Abderhalden 

 and his co-workers and other investigators for several purposes : 



/. Detection of Proteoclastic Enzymes. 



The hydrolysis of glycyl-1-tyrosine and other dipeptides containing 

 tyrosine or cystine is very readily observed as these compounds con- 

 tain amino acids, which are soluble with difficulty in water and which 

 gradually crystallise out as hydrolysis proceeds. 



Glycyl-1-tyrosine, which can be readily prepared, has therefore been 

 repeatedly used for the purpose of detecting proteoclastic enzymes. 



Instead of employing this synthetical dipeptide, Bergell and Schiitze 

 suggested the use of the peptone obtained by the hydrolysis of silk. 

 Abderhalden and Schittenhelm * have found that it is more convenient 

 than the glycyl-1-tyrosine as it is more soluble in water, contains more 

 tyrosine and is readily prepared. Abderhalden and Steinbeck describe 

 its preparation as follows : 



Silk-cuttings (i kilo.) are dried at 100 C. for forty-eight hours and 

 then placed in three to five times the quantity of 70 per cent, sulphuric 

 acid. The acid solution is allowed to stand for four days at 25 C, 

 when it is diluted with ten times the quantity of water ; the vessel in 

 which it is contained is kept cold with ice during the process of dilution. 

 Sulphuric acid is removed by adding, with continual stirring, the calcu- 

 lated quantity of powdered barium hydroxide ; after twelve hours the 

 barium sulphate is filtered off and washed several times with water by 

 stirring up in a mortar and decanting or filtering. The precipitate 

 should not be boiled with water in case neutralisation has not been per- 

 fect. The filtrate and washings are tested for barium and sulphuric acid, 

 and when these are found absent, they are evaporated to a small volume 

 in vacua at 40 C. ; if frothing occurs the evaporation may be effected 

 by dropping the solution into the evacuated flask through a tap funnel. 

 The solution is now again tested for barium and sulphuric acid. If 

 present they can be removed by warming to 60 C. and adding the 

 exact quantity of the necessary reagent. When these substances are 

 absent, the solution is evaporated in vacuo to a thick syrup. The syrup 

 is poured into absolute alcohol when the peptone separates in pale 

 yellow or white flakes. As soon as syrup begins to separate it is 



1 They state that this compound is supplied by Hoffmann La Roche & Co. in Basle 

 under the name " Peptone Roche ". 



