CHEMICAL COMPOSITION OF PROTEIN MOLECULE 47 



Globulins. 



The globulins, which can be prepared in a crystalline state, have 

 all a very similar composition. Excelsin contains the greatest amount 

 of arginine and edestin of glutamic acid. These proteins form the 

 best source of arginine. Their content in glutamic acid is about half 

 the content of the gliadins in this amino acid. 



No great difference is to be noted between the crystalline globulins 

 and the other vegetable globulins, except in the proportion of arginine 

 which is distinctly less in most of the non-crystalline ones. 



The legumins of the pea and vetch show no real difference in 

 their physical properties and elementary composition, but the analysis 

 shows that differences do exist, especially in the data for lysine and 

 histidine. Analysis has also shown that vignin ' differs from the other 

 legumins. 



The vicilin of the pea contains less sulphur (0*1-0*2 per cent.) 

 than any other protein ; its analysis shows that it is distinct from 

 legumin. It contains no glycine and more glutamic acid than legumin. 

 A similar protein does not exist in the vetch. 



Amandin contains 19 per cent, of nitrogen; the high content in 

 arginine and ammonia serve to explain this high figure. 



The high figure for valine in Foreman's analysis of the protein of 

 linseed is remarkable. 



Gliadins and Glutelins. 



There is a very marked difference in the composition of the two 

 proteins found in cereals. Those amino acids, which are absent in the 

 alcohol-soluble protein, are present in the other protein, which is 

 soluble in dilute alkali. The mixture (gluten) of these proteins in the 

 grain, therefore, gives all the amino acids present in other proteins. 



The gliadins are very like one another in composition. They are 

 distinguished from other proteins by their high content in glutamic 

 acid, proline and ammonia, their low content in arginine and histidine, 

 and the absence of lysine. On account of the high content in proline 

 and ammonia Osborne suggested the name of prolamines for this 

 group ; the group name gliadins has been preferred by the British 

 workers. 



Wheat-gliadin and rye-gliadin show no great differences, and it 

 seems probable that they are the same protein. Zein of maize differs 

 from them in containing no glycine and no tryptophane and also in con- 



