PROTEINS III 



Gluten: Preparation and Tests. 1 To about 50 grams of wheat flour in a 

 casserole or evaporating dish, add a little water and mi* thoroughly until a stiff 

 dough results. Knead this dough thoroughly and permit it to stand for about a 

 half hour. This is done in order that the maximum quantity of gluten may be 

 obtained. Treat the dough with about 200 c.c. of water and knead it thoroughly. 

 Note the yellowish color of the dough and the milky appearance of the water due 

 to suspended starch granules. (Place a drop of the suspension on a slide, cover 

 with a cover slip, run underneath the slip a drop of iodine solution and observe 

 the stained starch granules under the microscope.) Filter and apply a protein 

 color reaction (see page 97) to the nitrate. It should be positive indicating 

 that water-soluble proteins were present in the flour. Add fresh water to the 

 dough and repeat the kneading process. Continue this procedure with fresh 

 addition of water until practically no starch granules are noted in suspension. 

 To a small piece of the yellow, fibrous gluten apply Millon's Reaction (page 97). 

 This test shows gluten to be protein material. Utilize the remainder of the 

 gluten in the preparation of gliadin (page 112). 



Glutenin : Preparation and Tests. (In the preparation of gliadin (page 112) 

 it is customary to remove this prolamin from the crude gluten by extracting with 

 70 per cent alcohol. Inasmuch as gluten consists chiefly of gliadin and glutenin 

 the portion of the gluten remaining after the extraction of the alcohol-soluble 

 protein gliadin may be utilized for the preparation of glutenin.) 



To the finely divided residue from the preparation of gliadin (page 112) in a 

 flask or bottle add about 250 c.c. of 70 per cent alcohol. Allow to stand for about 

 48 hours with repeated shaking. This alcohol treatment will remove the gliadin 

 and leave crude glutenin. To purify the glutenin treat it in a mortar, with suffi- 

 cient 0.2 per cent NaOH to dissolve it, and filter the liquid through a wet pleated 

 filter. Neutralize the filtrate carefully, with 0.2 per cent HC1 adding the acid 

 drop by drop with thorough mixture after each addition. (The glutenin is sol- 

 uble in excess of acid.) Filter off the glutenin precipitate and wash several 

 times with 70 per cent, alcohol and finally with water. Apply the following tests : 



1. Solubility in water, salt solution, 0.2 per cent HC1 and 0.5 per cent Na2CC>3. 



2. Millon's Reaction. 



Prolamins (Alcohol-soluble Proteins) 



The term prolamin has been proposed by Osborne for the group of 

 proteins formerly termed "alcohol-soluble proteins." The name is 

 very appropriate inasmuch as these proteins yield, upon hydrolysis, 

 especially large amounts of proline and ammonia. The prolamins are 

 simple proteins which are insoluble in water, absolute alcohol and other 

 neutral solvents, but are soluble in 70 to 80 per cent alcohol and in dilute 

 acids and alkalis. They occur widely distributed, particularly in the 

 vegetable kingdom. The only prolamins yet described are the zein of 

 maize, the hordein of barley, the gliadin of wheat and rye, and the bynin 

 of malt. They yield relatively large amounts of glutamic acid on hy- 



1 This experiment as well as those on glutenin and gliadin which follow have been 

 adapted from directions given in Laboratory Notes of Professor Gies, College of Physicians 

 and Surgeons, New York. 



