THE PROTEINS 5 



OCCURRENCE AND CHARACTERISTICS OF DIFFERENT 

 CLASSES OF PROTEINS 



A. Simple Proteins 



Albumins are simple proteins that are soluble in 

 pure water and are coagulable by heat. Globulins, 

 on the other hand, are insoluble in pure water but 

 are readily soluble in dilute salt solutions. Albumins 

 and globulins are generally found together in nature 

 occurring, for example, in large quantity in the blood 

 serum, white of egg, in the substance of cells in gen- 

 eral, and in various seeds. Egg white may be divided 

 into two parts by dialysis against distilled water 

 the globulin being precipitated owing to the diffusion 

 of the salts from the solution which originally were 

 present in quantity sufficient to hold the globulin in 

 solution. 



Glutelins are simple proteins insoluble in all neu- 

 tral solvents but easily soluble in very dilute acids and 

 alkalies. Alcohol-Soluble Proteins are simple proteins 

 readily soluble in relatively strong alcohol (70 to 80 

 per cent), but are insoluble in water, absolute alco- 

 hol and other neutral solvents. These two groups of 

 proteins occur together as constituents of the cereal 

 grains. Glutenin and Gliadin, respectively, from 

 wheat, are the best known examples of these two 

 groups. They constitute the gluten of flour. The 

 elasticity and strength of the gluten, and therefore the 



