VIII] THE PROTEINS AND PROTEASES 133 



through muslin, and then through filter-paper. Dialyze the extract for 24 hrs. Then 

 filter oflF the precipitate of globulin which will have separated out, and dissolve 

 in 10 7n 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 takes place, (iii) Add a little 

 acid : the protein is precipitated. 



(f) Extraction of the prolamin, zein. The residue after salt extraction is then 

 extracted with 250 c.c. of hot 95 % alcohol. Filter, and concentrate the filtrate, 

 which contains the zein, on a water-bath (or, better, distil in vacuo). Pour a few 

 drops of the concentrated extract into (1) absolute alcohol, (2) distilled water. As 

 in the case of gliadin and hordein, a precipitate of zein will be formed. Then pour 

 the whole extract, after evaporating to a small bulk, into excess of distilled water, 

 and add a little solid sodium chloride. The precipitate of zein will slowly settle, and 

 can be filtered off. Zein is not readily soluble in acids and alkalies. Hence Millon's 

 and the xanthoproteic tests should be made on the solid material. Zein does not 

 contain the tryptophane nucleus. To demonstrate this, the glyoxylic reaction should 

 be made by shaking up some solid zein in reduced oxalic acid and adding sulphuric 

 acid and mixing. No purple colour is formed. 



{d) Extraction of glutenin. Take about half of the residue after the alcoholic 



extraction, pound in a mortar, and extract again with alcohol. Then extract the 



residue with O'l <'/o caustic potash solution. Filter off' the extract which contains 



N 

 the glutenin. To a portion of the filtrate add — sulphuric acid drop by drop. 



A precipitate of glutenin is formed. Test the remainder of the filtrate for proteins 

 [Expt. 121, (a)-(t^)]. 



Proteins of Leguminous Seeds (Leguminosae). 



In the Leguminosae, which are starchy seeds, the chief reserve 

 proteins, as contrasted with those of cereals, are globulins. The various 

 proteins occurring may be enumerated as : 



Legumin. A globulin which forms the chief protein in the seeds of 

 the Broad Bean {Vicia Foba), the Pea (Pisum sativum), the Lentil 

 (Ervum Lens) and the Vetch ( Vicia sativa). Legumin itself is soluble 

 in water, but occurs as salts which are insoluble in water and soluble 

 in saline solutions. Some portion can be extracted from the seed by 

 water only. 



Vicilin. A globulin occurring in smaller quantities than legumin 

 and found only in the Pea, Bean and Lentil seeds. 



Phaseolin. A globulin forming the bulk of the protein of the 

 Kidney Bean (Phaseolas vulgaris). 



Conglutin. A globulin forming the bulk of the protein in Lupin 

 {Lupinus luteus) seeds. 



