324 PROTEINS 



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 



Glutelins. This is a small class represented by two proteins, 

 both of vegetable origin, namely, 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 or acid. 

 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 

 ammonia, but only small amounts of arginine and histidine, 

 and no lysine. 



Glutelins and gliadins are the chief protein constitu- 

 ents of the substance known as gluten. 



Sclero-proteins. This term is synonymous with the older term 

 albuminoid, and includes substances of skeletal origin, 

 such as keratin from hair, horn, etc., gelatin, elastin, and 

 silk fibroin. 



No representative of this class has as yet been found 

 among vegetable proteins. 



