IX] PROTEINS AND AMINO- ACIDS 145 



endosperm or of the storage tissue of the cotyledons : others are proteins 

 of the protoplasm and nuclei of the tissues of the embryo and of the 

 endosperm. 



Proteins of Cereals {Gramineae). 



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, 16). 



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. 



JSxpt. 135. 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 coflfee-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-purap. Reserve 

 the residue on the filter and test the filtrate for proteins [Expt. 127, (a)-(fl?)]. 



Boil a second portion of the filtrate. 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. Also make the following 

 special tests for proteoses (Expt. 133). (i) Add a few drops of strong nitric acid. A 

 white precipitate is formed which disappears on heating gently and reappears on 

 cooling, (ii) Add one drop of strong acetic acid and two drops of 5 7o potassium 

 ferrocyanide solution. A white precipitate is formed which disappears on heating 

 gently and reappears on cooling. 



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

 a filter-pump. Then extract with 250 c.c. of 10 % 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 off the precipitate, which will be very slight, 

 and dissolve it in a little 10 7o sodium chloride. (Though so little globulin is present, 

 the experiment is instructive for comparison with the large amount of globulin ob- 

 tained from many other seeds.) Make the tests for protein [Expt 127, (a)-(ciO] 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. 



o. 10 



