450 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



THE COAGULABLE PROTEINS OF PLANTS. 



Coagulable proteins are present in various parts of plants, but are 

 particularly abundant in oil and leguminous seeds, in which they 

 form the reserve protein of the endosperm. The amount of pro- 

 tein in the seeds is determined by a nitrogen estimation by Kjeldahl's 

 method, but since the vegetable proteins contain more nitrogen than 

 animal proteins the factor 5-68 is employed instead of 6*25. The pro- 

 tein content of various seeds is as follows : 



Dried haricot beans 14 to 25 per cent. 

 lentils . . 19 to 24 

 ,, peas . . 19 to 23 

 Nuts . . . 15 to 28 ,, 



Vegetables and fruits contain from 1-1*5 P er cent, of protein, 

 the edible portion of beans about 7 per cent. 



Globulin forms the greater part of the protein of the seeds, but 

 small amounts of albumin are also present. 



It seems that the pea, horse bean, lentil and vetch contain the 

 same principal protein, the globulin termed legumin. In the three 

 first mentioned there is also another globulin termed vicilin. These 

 globulins are separated from one another by fractional precipitation 

 with ammonium sulphate. These seeds contain small quantities of 

 the albumin, legumelin. 



The oil seeds also contain globulins as their principal protein. 

 Many of them have been obtained in a crystalline form. The amount 

 of albumin in them is very small. 



The albumin, termed leucosin, is present in wheat in small quantities 

 and similar albumins are present in other cereals. 



They make up from '2-2 per cent, of the total protein. 



Globulins from Leguminous Seeds (Pea). 



Preparation. 



Pea flour (10 gm. or more) is stirred up with twice its weight of 10 

 per cent, sodium chloride solution and allowed to stand for about an hour. 

 The liquid is filtered from the insoluble residue which consists mainly of starch 

 (as shown by iodine test) and saturated with ammonium sulphate crystals (80 

 gm. per 100 c.c.). The legumin and vicilin are precipitated and filtered off. 

 They are dissolved in dilute ammonium sulphate solution (y^j- saturated) 

 and saturated ammonium sulphate solution is added in the proportion of 150 

 c.c. to 100 c.c. of solution ( T 8 ^ saturation). The legumin is precipitated ; it is 

 purified by repeating the process of precipitation with ^ saturated ammonium 

 sulphate and separated by dialysis. The filtrate from the legumin is saturated 

 with ammonium sulphate. The vicilin is precipitated and purified by solution, 

 *fo saturation and complete saturation as above and finally separated by dialysis. 



These proteins can be extracted with sodium benzoate solution (see under 

 edestin). 



Properties. 



These globulins have the same properties as other globulins ; they are 

 insoluble in water and are precipitated by pouring their solutions in salt 

 into a large volume of water or by dialysis. 



Legumin dissolved in 10 per cent, sodium chloride does not coagulate 

 on boiling. Vicilin is coagulated under the same conditions. 



