426 PROTEINS 



The vegetable globulins, which form the major portion 

 of the reserve proteins of all seeds except cereals, do not 

 always conform to these conditions of solubility. Thus, 

 whereas animal globulins are insoluble in water and are 

 precipitated by half-saturation with ammonium sulphate, 

 a great many globulins from plants are precipitated at 

 less than half saturation, and, on the other hand, some are 

 not precipitated until the solution is almost saturated with 

 ammonium sulphate. It must, however, be noted that 

 globulins extracted from seeds are nearly always obtained 

 in the form of salts with a small amount of acid, and so 

 long as they are in this form they have the characteristic 

 solubilities of animal globulins. As soon, however, as the 

 acid is removed they lose these and become completely 

 soluble in water. 



A further point of difference between animal and 

 vegetable globulins is that many of the latter are only 

 coagulated by heat with considerable difficulty. 



The albumins and globulins are the only classes of 

 proteins which are coagulated with heat. 

 Ghitelins. — This is a small class represented by two proteins, 

 both of vegetable origin, nam.ely, glutenin found in wheat 

 and oryzenin in rice. Similar substances probably occur 

 in other cereals as well, but owing to the difficulty of 

 obtaining them in a pure condition, they have not as yet 

 been investigated. 



Glutelins are insoluble in water and neutral saline 

 solutions, but dissolve in dilute alkali. 

 Gliadins or Prolamins. — These also are represented only by 

 vegetable proteins, namely, gliadin from wheat or rye, 

 hordein from barley, and zein from wheat or maize. Up 

 to the present they have only been found to occur in 

 cereals. The gliadins differ from all other proteins in being 

 soluble in 70-90 per cent alcohol, the solutions being un- 

 altered by boiling ; they are insoluble in water or in salt 

 solutions, but are soluble in dilute acids or alkalis. 



On hydrolysis they yield a considerable quantity of 

 proline (hence the name prolamins), glutamic acid and 



