PROTEINS 



ICQ 



(5) Dissolve the remainder of the edestin in 0.2 per cent hydrochloric acid 

 and preserve this acid solution for use in the experiments on proteans (see page 

 114). 



Tests on Edestin Filtrate. (i) Influence of Protein Precipitants. Try a 

 few protein precipitants such as nitric acid, tannic acid, picric acid, and mercuric 

 chloride. 



(2) Biuret Test. 



(3) Coagulation Test. Boil some of the filtrate in a test-tube. What 

 happens? 



(4) Saturation with Sodium Chloride. Saturate some of the filtrate with 

 solid sodium chloride. How does this result differ from that obtained upon 

 saturating egg albumin solution with solid sodium chloride? 



FIG. 38. EXCELSIN, THE PROTEIN OF THE BRAZIL NUT. 

 (Drawn from crystals furnished by Dr. Thomas B. Osborne, New Haven, Conn.) 



(5) Precipitation by Dilution. Dilute some of the filtrate with 10-15 volumes 

 of water. Why does the globulin precipitate? 



Glutelins 



It has been repeatedly shown, particularly by Osborne, that after 

 extracting the seeds of cereals with water, neutral salt solution, and 

 strong alcohol, there still remains a residue which contains protein 

 material which may be extracted by very dilute acid or alkali. These 

 proteins which are insoluble in all neutral solvents, but readily soluble 

 in very dilute acids and alkalis are called glutelins. The only member 

 of the group which has yet received a name is the glutenin of wheat, 

 a protein which constitutes nearly 50 per cent of the gluten, the re- 

 mainder being principally gliadin. It is not definitely known whether 

 glutelins occur as constituents of all seeds. 



