132 THE PROTEINS AND PROTEASES [CH. 



and test for proteins. All the tests will be positive : in the case of the xanthoproteic, 

 the precipitate disappears on heating and reappears on cooling, a characteristic of 

 proteoses (Expt. 126). Make also the special test for proteoses : Add a little potas- 

 sium ferrocyanide and acetic acid. A white precipitate is formed which disappears 

 on heating and reappears on cooling. 



(b} Extraction of the globulin. To the barley residue, after extraction with 

 water, add 250 c.c. of 10 / sodium chloride and allow the mixture to stand for 

 12-24 hrs. Filter first through muslin and then filter-paper, and put the extract 

 to dialyze for 24 hrs. Filter off the precipitate of globulin which will have formed, 

 and take it up into solution again in as small a quantity as possible of 10 % sodium 

 chloride. Make with the solution the following tests : (i) The usual (except Millon's) 

 tests for proteins [Expt. 121, (a)-(d)] : these will give positive results, (ii) Boil a little 

 of the solution : imperfect coagulation will take place, (iii) Add a little acid : a pre- 

 cipitate is formed, as is usual with plant globulins. 



(c) Extraction of the prolamin, hordein. The residue, after the sodium chloride 

 extraction, is then extracted with 250 c.c. of warm 95 / alcohol. Filter, and con- 

 centrate the filtrate on a water-bath (or better, distil in vacuo). After concentration, 

 test a little filtered extract as follows : pour a few drops into (1) absolute alcohol, 

 (2) distilled water. A white precipitate of hordein is produced in each case, since, 

 like gliadin, it is insoluble in both strong alcohol and water, but soluble in dilute 

 alcohol. Then pour the whole extract into a large volume of water. The protein is 

 precipitated as a fine white suspension, but will settle out more readily if a little 

 solid sodium chloride is added. Filter off the hordein, and dissolve in 1 % acetic acid. 

 Make the usual protein tests [Expt. 121, (a)-(rf)] ; there will be a positive result in 

 each case. 



In the Rye (Secede cereale) grain there are small percentages of 

 proteose, and of leucosin and edestin. The greater part of the protein 

 is gliadin, said to be identical with that in wheat. 



In the Maize (Zea Mays) grain there is apparently no true albumin, 

 though there is some proteose. There are small quantities of globulin, 

 but the greater part of the protein is a prolamin, termed zein, and a 

 glutenin (Osborne, 10). 



Expt. 131. Extraction of proteins of the Maize grain, (a) Extraction of proteins 

 soluble in water. Grind up 100 gms. of maize grains in a coffee-mill, or preferably use 

 maize meal. Add 250 c.c. of water and allow the mixture to stand 1-4 hrs. Filter 

 off, first through muslin, and then filter-paper. The filtrate contains proteose and 

 probably a little globulin which has gone into solution owing to the presence of salts 

 in the seed. Make the usual tests for protein [Expt. 121, (a)-(rf)]. 



Boil another portion of the filtrate. Some coagulation of protein will take place. 

 Filter, cool the filtrate and test for protein [Expt. 121, (a)-(d)]. Positive results will be 

 given by the proteose present. Make also the special test for proteoses : Add a little 

 potassium ferrocyanide and acetic acid. A white precipitate is formed, which dis- 

 appears on heating and reappears on cooling. 



(6) Extraction of globulin. The residue, after water extraction, is next treated . 

 with about 250 c.c. of 10% sodium chloride solution for 12-24 hrs. Filter, first 



