CHEMICAL COMPOSITION OF PLANTS 73 



The physiological significance of the splitting of proteins during 

 the germination of seeds consists in the fact that these proteins 

 first of all must be transformed into a conveniently mobile form, 

 since they must be transported from the reserve tissues, such as 

 the endosperm and the cotyledons, into the growing parts of the 

 developing embryo. Moreover, reserve proteins are only 

 slightly soluble or entirely insoluble; and, even in a dissolved 

 form, they are unable to diffuse through the cell membranes, 

 owing to their colloidal nature. Another no less important result 

 of the breaking down of proteins into amino acids is their loss 

 of specific nature. Every protein being characterized by a 

 combination of amino acids specific to it, it is not possible there- 

 fore to change one protein directly into another. In order to 

 do this, it is necessary first to decompose it into its simplest 

 integral parts, and only then may they be combined into a new 

 protein molecule. This is attained by a complete destruction 

 of the protein molecule into the end products of its hydrolysis. 



A part of the amino acids formed during disintegration of the 

 reserve proteins is not directly utilized in the construction of 

 new protein molecules on account of the differences in the com- 

 position of proteins stated above. These ''superfluous" amino 

 acids disintegrate further into ammonia and nitrogen-free sub- 

 stances by means of the activity of a special enzyme desamidase. 

 That is why ammonia is always found among the products of 

 disintegration in germinating seeds. It never accumulates in 

 significant quantities, however, for immediately after this last 

 stage of decompositio"n of proteins is attained in the seedling, 

 synthetic processes commence, which greatly complicate the 

 general picture of the metabolism of nitrogenous substances 

 during germination. Boussingault (1864) has pointed out the 

 fact that in germinating seeds, especially in legumes rich in 

 reserve proteins, there accumulates a large quantity of aspara- 

 gine, an amide of aspartic or aminosuccinic acid, 



CONH2— CH2— CHNH2— COOH. 



He expressed the idea that asparagine is analogous to the 

 amide that accumulates in the blood of animals, viz., urea, 

 NII2CONH2. The production of asparagine is a way of fixing 



