186 THE PROTEINS AND PROTEASES [ch. 



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. The following 

 is a short account of the occurrence of some of the amino-acids in the 

 free state (see also p. 120). 



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

 (Lupinus) and Kidney Bean (Pha.seolus). 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 (Pisiim) and 

 Goosefoot {Ghenopodium). 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. 



Isoleucine has been extracted from seedlings of Vicia sativa. 



Aspartic acid. The amide of this acid, i.e. asparagin, 

 CONHo • CHo • CHNHo • COOH 

 is widely distributed in plants. It is present in shoots of Asparagus 

 from which it derives its name. It has also been extracted in very 

 considerable quantities from etiolated seedlings of Vicia, Lupin, and from 

 various plants such as Potato, Dahlia, Garden Nasturtium (Tropaeolum), 

 Cucurbita and Sunflower (Helianthus). 



Glutaminic acid. The amide, again, of this acid, i.e. glutamine, 



CONH. • CHo • CH2 • CHNH„ • COOH 



is widely distributed. It has been isolated from seedlings of Cucurbita, 



Lupinus, Helianthus, Castor-oil plant (Ricinus), Spruce Fir (Picea excelsa) 



and a number of Cruciferae. 



Arginine has been isolated from seedlings of Lupinus, Cucurbita, 

 Vicia, and Pisum. It is especially abundant in the seedlings of some 

 Coniferae, i.e. Picea excelsa. Silver Fir {Abies pectinata) and Scotch Fir 

 {Pi^ms sylvestris). It also occurs in roots and tubers, as for instance in 

 those of the Turnip {Brassica campestris), Artichoke {Helianthus tubero- 

 sus), Chicory {Cichorium Intybus), Beet {Beta vulgaris), Potato and 

 Dahlia, and in the inner leaves of the Cabbage {Brassica oleracea). 



