112 PHYSIOLOGICAL CHEMISTRY 



drolysis but no lysin. The largest percentage of glutamic acid (43.66 

 per cent) ever obtained as a decomposition product of a protein sub- 

 stance has very recently been obtained by Osborne and Guest from the 

 hydrolysis of the prolamin gliadin. 1 This yield of glutamic acid is also 

 the largest amount of any single decomposition product yet obtained 

 from any protein except protamines. 



Gliadin : Preparation and Tests. Introduce the finely divided crude gluten 

 as prepared on page 1 1 1 into a flask or bottle, add about 250 c.c. of 70 per cent 

 alcohol 2 and allow the mixture to stand 24 hours with occasional shaking. Filter 

 (retaining the undissolved portion for preparation of glutenin, page 1 1 1 ) , evaporate 

 the filtrate to dryness in a porcelain dish over a water-bath. Pulverize the dry 

 material. Apply the following tests to this gliadin powder : 



Solubility and Protein Tests. Test the solubility in alcohol (30 per cent, 

 50 per cent and 70 per cent), water, 0.9 per cent NaCl, 0.2 per cent HC1 and 0.5 

 per cent Na 2 CO 3 . Shake each test repeatedly and filter. To the filtrate apply 

 Coagulation test (page 105) and Biuret test (page 98). 



Albuminoids (Scleroproteins) 



The albuminoids yield similar hydrolytic products to those obtained 

 from the other simple proteins already considered, thus indicating that 

 they possess essentially the same chemical structure. They differ from 

 all other proteins, whether simple, conjugated, or derived, in that they 

 are insoluble in all neutral solvents. The albuminoids include "the 

 principal organic constituents of the skeletal structure of animals as 

 well as their external covering and its appendages. ' ' Some of the princi- 

 pal albuminoids are keratin, elastin, collagen, reticulin, spongin, and 

 fibroin. Gelatin cannot be classed as an albuminoid although it is a 

 transformation product of collagen. The various albuminoids differ 

 from each other in certain fundamental characteristics which will be 

 considered in detail under Epithelial and Connective Tissue (sec 

 Chapter XVIII). 



CONJUGATED PROTEINS 



Conjugated proteins consist of a protein molecule united to some 

 other molecule or molecules otherwise than as a salt. We have glyco- 

 proteins, nucleoproteins, hemoglobins (chromoproteins), phosphoproteins 

 and lecithoproteins as the five classes of conjugated proteins. 



Glycoproteins may be considered as compounds of the protein mole- 



1 Osborne and Guest: Jour. Biol. Chem., 9, 425, 1911. Up to this time the yield of 

 41.32 per cent obtained by Kleinschmitt from hordein was the maximum yield. 



2 Bailey and Blish claim that 50 per cent alcohol is more satisfactory (Jour. Biol. 

 Chem., 23,345, 1915)- 



