178 NUCLEIC ACIDS AND THE NITROGENOUS BASES 



colorless residue which does not turn red or violet on heating with 

 alkali. With hydrochloric acid and zinc and subsequent addition of 

 alkali an adenine solution yields a ruby-red color which changes to a 

 brownish tinge. Adenine has been obtained from certain pathological 

 urines (leukemia) and it occurs in considerable amounts in tea-leaves. 



THE STRUCTURE OF THE NUCLEIC ACIDS. 



The nucleic acid of yeast appears to be identical with the nucleic 

 acid of the wheat-kernel, Tritico-nucleic Acid. It yields, on complete 

 hydrolysis, two purine bases and two pyrimidine bases, namely, 

 guanine, adenine, cytosine and uracil. 



When yeast nucleic acid is heated in neutral solutions under pressure 

 to 175 C. it splits off phosphoric acid and yields four different Nucleo- 

 sides each consisting of a molecule of purine or pyrimidine base united 

 to a molecule of a-ribose. These nucleosides are the following: 



Guanosine ..... ......... 



Adenosine .............. 



Cytidine ............... 



Undine ........... .... C B H9O4.C4H 3 N 2 O2 



It follows that in the undecomposed molecule of nucleic acid the 

 purine and pyrimidine bases must be attached directly to the a-ribose 

 molecules. The nucleosides do not reduce Fehling's Solution and 

 hence the carbohydrate radical must be united to the basic radical in 

 such a way as to involve destruction of the actual or potential aldehyde 

 structure of the sugar, in other words these compounds are analogous 

 to the Glucosides. 



If, instead of hydrolyzing nucleic acid with the aid of heat or inor- 

 ganic catalyzers, we employ extracts of various organs, such as the 

 kidney, heart-muscle, liver, pancreas, or intestinal mucosa, or if we 

 employ blood-serum or hemolyzed blood, all of which contain the 

 enzyme Nuclease, the nucleic acid is split into four different Mono- 

 nucleotides each of which, on intense hydrolysis, yields phosphoric acid, 

 a carbohydrate which in the case of yeast nucleic acid is a-ribose, and 

 one of the four different purine and pyrimidine bases which the original 

 molecule contained. The molecule of nucleic acid is, therefore, a 

 Tetranucleotid, built up out of the union of four mononucleotid 

 radicals. 



Two mononucleotids are known to occur in animal tissues, they are 

 Guanylic Acid, obtained by the partial hydrolysis of /3-nucleoproteins, 

 those nucleoproteins which may be extracted from a variety of tissues 

 by Boiling Water, and Inosinic Acid which exists as such in most 

 extracts. 



When guanylic acid is completely hydrolysed by mineral acids it 

 yields phosphoric acid, a-ribose and guanine. It yields no other 

 purine base and no pyrimidine bases. By means of hydrolysis in 



