DETERMINATION OF STRUCTURE OF PROTEINS 83 



4. Glycyl-valine anhydride, which was identical in its properties, 

 except the melting-point, with the synthetical compound. 



From gliadin Fischer and Abderhalden have isolated the dipeptide 

 1-leucyl-d-glutamic acid, which they identified with the synthetical sub- 

 stance ; from caseinogen Abderhalden and Funk have isolated leucini- 

 mide and 1-phenylalanyl-d-alanine anhydride and probably also leucyl- 

 valine anhydride. 



Osborne and Clapp obtained a crystalline substance by the acid 

 hydrolysis of gliadin. It yielded proline and phenylalanine on further 

 hydrolysis. Fischer and Luniak in 1909 identified it as 1-prolyl-l- 

 phenylalanine. 



Levene and Beatty have isolated an anhydride, composed of glycine 

 and proline, from the products resulting by a prolonged trypsin digestion 

 of gelatin. This substance was optically inactive, but was again ob- 

 tained by Levene in an optically active state by a shorter digestion. 

 Its rotation, however, was still lower than the synthetical compound 

 prepared by Fischer and Reif, but the compounds are probably identical. 



Further investigations have been carried out by Abderhalden. He 

 has isolated 1-leucyl-d-alanine from the mother liquor of the elastin 

 from which d-alanyl-1-leucine was obtained. From edestin two com- 

 pounds were separated but not in a pure state ; the one contained glu- 

 tamic acid and tryptophane, the other contained leucine, glutamic acid 

 and tryptophane. Neither compound was identical with the syntheti- 

 cal preparations which were prepared for comparison with them. 



The presence of glycyl-1-tyrosine in silk-fibroin was proved by its 

 isolation in a crystalline state in 1909. 



d-Alanyl-glycine was subsequently obtained jand thoroughly identi- 

 fied with the synthetical compound. This product can now be easily 

 prepared as follows : 



100 grammes of silk are covered gradually with three times the 

 quantity of 70 per cent, sulphuric acid, cooled to o C. Solution 

 begins immediately and is complete in about two hours. It is 

 then kept at 26 C. for four days, when it is diluted with 10 litres of 

 water, the mixture being kept cold by ice. The sulphuric acid is now 

 removed quantitatively with purified baryta and the filtrate is evapor- 

 ated in vacua at 40 C. The solution is tested from time to time for 

 baryta and sulphuric acid, and if either be present it is removed. The 

 barium sulphate is thoroughly washed with cold water and the wash- 

 ings concentrated in the same way. The residue obtained on complete 

 evaporation is treated with hot methyl alcohol, in which it almost 



6* 



