VIII] THE PROTEINS AND PROTEASES 131 



to dryness, and then poured into a large volume of distilled water. A milky precipi- 

 tate of gliadin is formed which may be made to settle by adding a little solid sodivmi 

 chloride and stirring. Filter oflf the gliadin and dissolve in 10 "/„ acetic acid. With 

 the solution make the tests for protein [Expt. 121, {a)-{d)]. 



(d) Extraction of gliitenin. Take half the wheat residue from the alcoholic ex- 

 traction, pound well in a mortar and extract again with warm alcohol and subsequently 

 with water. The residue must be free from water- and alcohol -soluble proteins as 

 they are also soluble in alkalies. Then extract the residue with O'l "/o caustic potash 

 .solution. Filter off the extract which contains the glutenin. To a portion of the 



N 

 filtrate add y- sulphuric ticid drop by drop. A precipitate of glutenin is formed. 



Test the remainder of the filtrate for proteins [Expt. 121, (a)-(c/)]. 



The gliadin of wheat has the peculiar property of combining with 

 water to form a sticky mass which binds together the particles of 

 glutenin, the whole forming what is termed gluten. It is this phenomenon 

 which gives the sticky consistency and elastic properties to dough. 



Expt. 1 29. To demonstrate the fact that gluten formation depends on the presence 

 of gliadin. Take two small evaporating dishes. Fill one with ordinary flour. Fill 

 the other with flour that has been extracted with 70 % alcohol for two or three days. 

 (The alcohol is allowed to stand on the wheat in the cold. It is then poured off", and 

 more added, and the process repeated. The flour is now dried again, first in air, then 

 in the steam-oven and finally is ground in a mortar.) A little water is added to 

 each of the dishes and the flour worked up into a dough. This is then allowed to 

 stand for half an hour. The dough consists of gluten (gliadin and glutenin) to which 

 the starch adheres. Next take two beakers, fill with water, and over the top of each 

 tie a muslin cover. Place the two samples of dough on the muslin on the two beakers, 

 and rub gently with a glass rod. The starch will be washed away into the beakers. In 

 the case of the normal flour a sticky mass of gluten will remain. In the other case 

 there will be no gluten on account of the absence of gliadin. To the suspension of 

 starch in the beaker add some iodine solution, and it will turn a deep blue-black colour. 



In the Barley {Hordeiim vulgare) grain, small percentages of an 

 albumin, apparently identical with leucosin, and of a globulin, barley 

 edestin, are present, together with some proteose. The main protein is 

 a prolamin, hordein, very similar to, but not identical with, gliadin. 

 There is no well-defined glutelin (Osborne, 9). 



Expt. 130. Extraction of the proteins of the Barley grain, (a) Extraction of the 

 albumin and proteose. Grind up 100 gms. of barley grains in a coffee-mill, or use 

 preferably barley flour. Add 250 c.c. of distilled water to the ground meal, and 

 allow the mixture to stand for 1-4 hrs. Filter ofl' the extract, first through muslin 

 and then through filter-paper. The extract will contain a small quantity of the 

 albumin, leucosin, and proteose. With the filtrate inake the tests for proteins 

 [Expt. 121, {a)~{d)]. 



Boil a second portion of the filtrate, A white precipitate of the coagulated pro- 

 tein is formed. Filter oft' the precipitate, cool the filtrate containing the proteose 



9—2 



