42 2 PROTEINS 



These facts are made use of in the extraction of the sub- 

 stances in question from vegetable tissues such as seeds, which 

 may contain several proteins ; and although the products so 

 obtained are anything but pure, a brief outline of the method 

 may be given. The separation of the proteins removed by 

 these means from the seed by a given solvent is a very lengthy 

 and tiresome process, and the details must be sought for 

 elsewhere.* 



Before proceeding with the extraction, the material must 

 be ground up as finely as possible, in order that all the cells 

 may be broken ; if needs be, the tissue must be carefully dried 

 beforehand, but too high a temperature must not be used. 



In all cases the initial procedure is much the same ; the 

 powdered material is well mixed with the solvent, which is 

 allowed to act for some time ; the mixture should be well 

 shaken periodically f The solid is then filtered off and well 

 washed with fresh solvent, and is again treated until the 

 extract gives no protein reaction. The temperature may be 

 raised during the extraction, but it should not be high enough 

 to alter the proteins. If the extraction, especially with aqueous 

 solvents, be prolonged, it may be necessary to add a little 

 antiseptic, such as chloroform, in order to stop bacterial action. 



When it is desired to make successive extracts, in cases 

 such as seeds where several proteins may be present, the order 

 may be water, lo per cent sodium chloride, alkali (-1 to -2 per 

 cent caustic potash or -5 to i per cent sodium carbonate), and 

 finally alcohol (70 to 80 per cent). 



The initial extraction may be made with salt solution, the 

 albumins being afterwards separated from the globulins, and 

 this course is recommended when both are present on account 

 of the saving of time. 



The proteins isolated by these means may be roughly 

 purified as follows : — 



* See Osborne : " The Vegetable Proteins," London, 1924, on whose 

 account the following is based. For a method for the preparation of plant 

 globulins, see Reeves : " Biochem. Journ.," 1915, 9, 508. 



t If the material employed is a fatty seed, a preliminary extraction 

 with ether is essential to remove the fat before treating with aqueous 

 solvents. 



