IX] PROTEINS AND AMINO- ACIDS 149 



A well-crystallized globulin can be obtained from the Linseed {Linum 

 usitatissimum) (Osborne, 9, 10), and a globulin, excelsin, from the Brazil nut 

 {Bertholletia excelsa) (Osborne, 10) also in crystalline or semi-crystalline 

 form. Similar globulins can be extracted from a number of other seeds, 

 i.e. Coconut (Cocos nucifera), Sunflower (Helianthus annuus), Cotton-seed 

 {Gossypium herbaceum), Mustard-seed (Brassica alba) and many others. 

 The fat is first removed from the ground seed by either ether or benzene; 

 the residue is then extracted with dilute sodium chloride and the extract 

 dialyzed. 



The Amino- Acids. 



There is every reason to believe, since they always arise in hydrolysis 

 of proteins, that amino-acids are universally distributed in the plant. 

 It is, however difficult to isolate and detect them, except in certain special 

 cases, as, for instance, in germinating seeds when a large store of protein 

 is being rapidly hydrolyzed and translocated. 



A point of interest in connection with amino-acids is the high per- 

 centage of glutaminic acid in many proteins especially those of the 

 Oramineae (35-40 7o) and Leguminosae (15-20 7o)- Moreover, since 

 glutaminic and aspartic acids have two carboxyl groups, only one will be 

 combined in the peptide linkage, the other being free. It appears that 

 the free carboxyl groups of these acids are, even in the protein, combined 

 with ammonia forming an amide, — CONHg. Consequently, when pro- 

 teins containing a high percentage of glutaminic acid are hydrolyzed 

 they yield a correspondingly high percentage (18-23 "/o) of "amide" 

 nitrogen, as ammonia, compared with other proteins (6-7 "/o)- Moreover, 

 as a result of hydrolysis in the plant itself the respective amides, glu- 

 tamine and asparagine, are formed and not the free acids. 



The following is a short account of the occurrence of some of the 

 amino-acids in the free state (see also p. 134). 



Valine has been isolated from seedlings of the Vetch ( Vicia), Lupin 

 (Lupinus) and Kidney Bean (Pltaseolus). It is present in larger amounts 

 in etiolated seedlings of Lupin than in the green plants. 



Leucine is widely distributed. It has been isolated from, seedlings 

 of Vicia, Vegetable Marrow (Cucurbita), Lupinus, Pea (Pisum) and 

 Goosefoot (Chenopodium), It has also been found in Phaseolus, Water 

 Ranunculus {Ranunculus aquatilis), buds of Horse Chestnut (Aesculus 

 Hippocastanum) and in small quantities in Potato tubers and other 

 plants. 



