CHEMICAL COMPOSITION OF PLANTS 77 



Purine and pyrimidine are heterocyclic nitrogen-containing 

 compounds. Their derivatives being substances of a basic 

 character, they will combine readily with phosphoric acid. The 

 carbohydrate group is most frequently represented by the 

 pentose, Z-ribose C5H10O5. In breaking down nucleoproteins 

 in the animal organism, the derivatives of purine most often give 

 uric acid. 



The proteins of the protoplasm have been studied very little. 

 In protoplasm, glucoproteins are often found; these are complex 

 proteins, which yield carbohydrate groups on hydrolysis. Fungi 

 are especially rich in glucoproteins. Protoplasm contains also 

 special phosphorus-containing proteins, which do not belong to 

 the nucleoproteins and are called ''plastins." Many authors, 

 including Lepeschkin, suppose that the proteins of protoplasm, 

 being of a very complex structure, are chemically bound still 

 further with Hpoids forming molecular complexes of an enormous 

 size and capable of the most varied biochemical reactions. It 

 was at one time supposed that ''living" proteins of the plasma 

 differ from ''nonliving" ones in that nitrogen is found in them 

 not in the form of the amino group, NH2, but in the form of the 

 cyanic group, — C:N, which gives them a special instabiUty 

 and high capacity for transformation — two essential properties 

 of life. This theory was first advanced by Pfliiger and was 

 supported for a long time by Loew and Bokorny, who by means 

 of a special aldehyde reaction attempted to distinguish chem- 

 ically between living and nonliving proteins. 



The most recent biochemical investigations do not support 

 this idea, and therefore there is no reason to believe that the 

 proteins of protoplasm are especially unstable. Quite the 

 contrary; in their relation to enzymes and to many chemical 

 reagents, they are usually more stable than the reserve proteins. 



Such processes of hydrolysis of reserve proteins and synthesis 

 of active proteins of the protoplasm also take place at the time 

 of resumption of growth by other storage organs. Asparagine, 

 for instance, accumulates in large quantities in the underground 

 sprouts of asparagus, from which it has received its name. 

 Considerable quantities of it are also to be found in the unfolding 

 leaves and flower buds of trees that have been kept in darkness; 

 but in the light, synthetic processes soon become dominant, pro^ 

 ceeding at the expense of the newly produced carbohydrates. 



