NUCLEIC ACIDS AND NUCLEOPROTEINS 125 



nucleosides. Many tissues however contain enzymes capable of 

 completing the decomposition with liberation of the carbohydrate and 

 basic radicals. The purine bases may also be deaminized while still 

 in combination as nucleosides and further hydrolysis would then lead 

 to the direct liberation of the oxypurines instead of their precursors, 

 the amino-purines. 



Jones 1 has suggested a method by which the course of the decom- 

 position of the nucleic acid molecule can be followed. By this means 

 it is readily shown that phosphoric acid is liberated at very different 

 rates from the different nucleotides. 



The following outline will indicate the course of decomposition of a 

 nucleic acid and the enzymes involved in the process. 



DECOMPOSITION OF NUCLEIC ACID 

 NUCLEIC ACID v 



(nucleicacidase of intestinal mucosa and juice) 



Purine Nucleotides Pyrimidine Nucleotides 



(nucleotidase of intestinal (tissue nucleases) 



mucosa and juice) 



F" I Sugar 



Phosphoric Acid Purine Nucleosides Phosphoric Acid 



I Pyrimidine Bases 



Cytosine and Thymine 

 (nucleosidase of tissues) or Uracil 



Sugar Purine Bases 



(pentose or hexose) Adenine 



Guanine 



With regard to the fate of the various radicals of the nucleic acids 

 in the body after absorption little is definitely known. The phosphoric 

 acid may of course be built up into phosphorus-containing cell con- 

 stituents such as nucleoproteins, phosphoproteins or phosphatides, or 

 be eliminated as. phosphate in the urine. The carbohydrate portion 

 may undergo the usual transformations of intermediary carbohydrate 

 metabolism. The nucleosides appear to be ordinarily absorbed un- 

 changed from the intestine and may be to a certain extent directly re- 

 synthesized in the animal body to nucleoprotein. The excess over body 

 requirement must, however, be decomposed, although a certain portion 

 may possibly be stored up in the individual cells or in certain organs. 

 Enzymes capable of decomposing nucleic acids are found in most of the 

 cells of the body. 



The Purine Bases. As has been indicated the basic substances 

 present in nucleic acid belong to two classes the purine and pyrimidine 



. l Jones: Presidential address before the Society of Biological Chemists, Boston, Dec. 

 27, 1915. 



