130 THE PROTEINS AND PROTEASES [ch. 



Proteins of Cereals {Graminaceae). 



As far as investigations have gone it may be said that the starchy- 

 seeds of cereals are poor in albumins and globulins. The chief reserve 

 proteins belong to the peculiar group of prolamins, and a considerable 

 portion also consists of glutelins. 



The grain of Wheat {Triticum vulgare) contains some proteose and 

 a small percentage of an albumin, leucosin. A globulin occurs only 

 in very small amount. The bulk of the protein consists of gliadin (a 

 prolamin) and of glutenin (a glutelin). Nucleoproteins are present in 

 the embryo, but there is no gliadin or glutenin (Osborne and Voorhees, 14). 



Expt. 128. Extraction of the proteins of the Wheat grain, (a) Extraction of 

 albumin {leucosin) and proteose. Take 100 gms. of white flour (the same quantity of 

 wheat grains which have been ground in a coffee-mill may be used, but the extraction 

 in this case is slower), put the ground mass in a large flask or beaker and add 

 250 c.c. of distilled water. Let the mixture stand for 1-4 hrs., shaking occasionally. 

 Filter off some of the liquid, first through muslin and then on a filter-pump. Reserve 

 the residue on the filter and test the filtrate for proteins [Expt. 121, (a)-(o?)]. 



Boil a second portion of the filtrate (after adding a drop or two of acetic acid). 

 A precipitate of the albumin, leucosin, is formed. Filter off this precipitate, cool the 

 filtrate and make the protein tests again. All the above tests are given by the proteose 

 in solution: in the case of the xanthoproteic, the precipitate disappears on heating 

 and reappears on cooling (Expt. 126). Also make the following special test for 

 proteoses (Expt. 126): Add a little potassium ferrocyanide solution and acetic acid. 

 A white precipitate is formed which disappears on heating and reappears on cooling. 



(b) Extraction of the globulin. Take the residue of ground wheat and drain on 

 a filter-pump. Then extract with 250 c.c. of 10 **/o sodium chloride solution for 

 12-24 hrs. Filter off, first through muslin, and then through paper on a filter- 

 pump. Put the extract to dialyze in a collodion dialyzer for 24 hrs. (toluol should 

 be added to the liquid in the dialyzer). Filter oft' the precipitate, which will be very 

 slight, and dissolve it in a little 10% sodium chloride. (Though so little globulin is 

 present, the experiment is instructive for comparison with the large amount of 

 globulin obtained from many other .seeds.) Make the tests for protein [Expt. 121, 

 (a)-{d)] with the solution (Millon's cannot be used on account of the presence of 

 chlorides). Also try the effect of (i) boiling the sodium chloride solution : coagulation 

 is not complete, (ii) adding a little acid: a precipitate is formed as in the case of 

 edestin. 



(c) Extraction of gliadin. Take the wheat residue, which has been filtered from 

 the sodium chloride solution, and add 250 c.c. of 95 f'/o alcohol. Warm on a water- 

 bath and filter. Evaporate the filtrate, which contains gliadin, on a water bath (or 

 better distil oft" the alcohol in vacuo). When reduced to about half its bulk, take a 

 little of the filtrate and filter. Divide this filtrate into two parts in test-tubes. To 

 one add water: to the other absolute alcohol. A white precipitate of gliadin is 

 formed in each case, since it is insoluble in both water and strong alcohol, though 

 soluble in dilute alcohol. The remainder of the gliadin extract is evaporated almost 



