THE INDIVIDUAL GROUPS OF PROTEINS 453 



Gliadin. 



Gliadin is not easily prepared from gluten, but is prepared from flour by 

 extracting it with hot alcohol (74 per cent, by volume). The alcohol extract 

 is concentrated in vacua and poured into absolute alcohol. The precipitate 

 may be dissolved in dilute alcohol and poured into absolute alcohol. 



Gliadin prepared as above forms an amorphous powder, but if prepared 

 by evaporation of the dilute alcohol it forms a yellow-brown sticky mass 

 which dries like glue. 



Gliadin is insoluble in water and in absolute alcohol, but dissolves in 

 dilute alcohol of 50-70 per cent. It is also insoluble in dilute salt solutions. 

 It dissolves slowly in warm acids and alkalies and is converted into deriv- 

 atives. 



It gives most of the general reactions for proteins. 



Besides its peculiar solubilities gliadin also differs considerably in composi- 

 tion from other proteins : it contains a large amount of proline and also amide 

 groups hence gliadins have been termed prolamins. They also contain a 

 large amount of glutamic acid. 



Wheat Glutelin or Glutenin. 



Glutenin is most easily prepared from gluten. The gluten is boiled 

 several times with alcohol and the residue dissolved in 0*2 percent, potassium 

 hydroxide. On neutral'sation of the solution with acetic acid, the glutenin is 

 precipitated and may be purified by repeating the solution in alkali and 

 precipitation with acetic acid. The precipitate is washed and dried with 

 alcohol and ether. 



Glutenin forms an amorphous powder which is insoluble in water and 

 in salt solutions, but soluble in -2 per cent, acid or alkali. It is converted 

 into derivatives by stronger acids and alkalies. It gives most of the general 

 reactions for proteins. 



