CHAPTER III. 



ISOLATION AND PREPARATION OF SEED PROTEINS. 



VARIOUS methods have been employed to isolate the different protein 

 constituents of the several seeds which have been examined, but as 

 essential modifications of the necessary procedure are required for 

 almost every one of these seeds it is impossible to give here an account 

 of the methods in sufficient detail to enable the reader to make practical 

 use of them in isolating and purifying preparations of the individual pro- 

 teins. He is therefore referred to the original papers in which the pro- 

 teins are described or to special publications dealing with this subject. 

 An outline of these methods and a consideration of the results which 

 can be expected from them deserves some discussion and will be dealt 

 with in this chapter. 



The solvents used to extract the proteins of seeds are water, neutral 

 saline solutions, 70 to 80 per cent, alcohol, and very dilute acids and 

 alkalies. By the successive application of these solvents the greater 

 part of the protein can be extracted from most seeds when finely ground, 

 but the residue, even after extracting as completely as possible, usually 

 contains more or less nitrogen. Although not definitely proved it is 

 probable that this nitrogen belongs largely to protein enclosed in cells 

 of the seed tissue which have escaped disintegration in grinding. In 

 most cases the amount of this undissolved nitrogen is so small that it 

 does not require further consideration. 



A. Extraction with Water. 



Water may dissolve several types of protein from the ground seeds, 

 namely, proteoses, albumins, globulins, soluble in very dilute saline 

 solutions, and such soluble compounds of any other proteins with acids 

 as may be present in the seed, or formed during extraction. It may, 

 as frequently happens with many of the leguminous seeds, also dis- 

 solve a relatively large proportion of protein soluble in water when 

 uncombined with acid but insoluble in the form of its salts, that is 

 when the protein is combined with a definite but small proportion of 

 acid. (See Chapter IV., p. 28.) 



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