CHAPTER IX. 

 THE NUCLEIC ACIDS AND THE NITROGENOUS BASES. 



THE DECOMPOSITION-PRODUCTS OF THE NUCLEIC ACIDS. 



The nucleic acids form the prosthetic group in an important series 

 of conjugated proteins, the Nucleoproteins. These substances usually, 

 but not invariably, occur in nuclear tissues and may be precipitated 

 from tissue-extracts by acidification with acetic acid,, in excess of 

 which they do not dissolve. The nucleoproteins dissolve, however, 

 in dilute mineral acids and in dilute alkalies; they are not soluble in 

 distilled water. Certain nucleoproteins designated the /3-nucleopro- 

 teins, however, are soluble in boiling water and are extracted from 

 tissues in this manner, leaving the other tissue-proteins in the form of 

 coagula in the insoluble residue; the jS-nucleoproteirs are also pre- 

 cipitable by acetic acid. 



When the alkali-compound of a nucleoprotein, dissolved in water, 

 is heated, a portion of the protein is split off in a coagulated form, 

 while the residue of the molecule, which still contains protein but is 

 much richer in phosphorus than the original nucleoprotein, remains 

 in solution. A similar cleavage is brought about by the Pepsin in 

 gastric juice, which digests the protein fraction which is split off from 

 the nucleoprotein, but leaves a residue undigested which still contains 

 protein united to nucleic acid. This residue is designated Nuclein. 



By means of more intense hydrolysis with alkali the nucleins are 

 split up into products of protein hydrolysis and the alkali salts of 

 the nucleic acids. These salts may be precipitated from concentrated 

 solutions by the addition of alcohol. 



Upon hydrolysis with acids all of the nucleic acids yield three widely 

 differing groups of products. In the first place phosphoric acid is an 

 essential constituent of the molecule, secondly a carbohydrate radical, 

 which may be either a pentose or a hexose, and thirdly a nitrogenous 

 base belonging to the group of Purine Bases or to the closely allied 

 group of Pyrimidine Bases. 



The carbohydrate radical differs essentially in nucleic acids of different 

 origin. In all of the plant-nucleic acids which have been investigated, 

 the carbohydrate radical has been found to be a pentose d-ribose: 



CHO 

 HCOH 



HCOH 

 HCOH 

 CH;OH 



