CHAPTER VI 

 NUCLEIC ACIDS AND NUCLEOPROTEINS 1 



The Nucleoproteins. The nucleoproteins occur widely distributed 

 in the animal and plant kingdoms, being found in nearly all cells and 

 particularly in the nuclei of cells. They are found in especially large 

 amounts in glandular tissues such as those of the thymus, pancreas and 

 spleen. The nucleoproteins are combinations of protein with a phos- 

 phorus-containing substance known as nucleic acid. As different nu- 

 cleic acids exist and are found in combination with different proteins, 

 a variety of nucleoproteins exist. The protein combined with the 

 nucleic acid is in certain cases a histone, the conjugated protein in 

 this case being called a nucleohistone. 



The nucleoproteins give the ordinary protein color reactions. 

 They are acidic in character and insoluble in water. They are readily 

 soluble in weak alkali but are precipitated from such solution on the 

 addition of acetic acid in excess of which they dissolve with more or 

 less difficulty although readily soluble in very dilute hydrochloric acid. 

 We distinguish them from mucins, which are likewise precipitated by 

 acetic acid through the fact that the latter give no tests for phosphorus 

 on decomposition. 



The nucleoproteins are very complex and unstable substances 

 and one has probably never been prepared in a pure form. Under the 

 action of the gastric juice or of weak acid nucleoproteins lose a portion 

 of their protein content and are transformed into a rather ill-defined 

 class of substances known as nucleins which still possess some protein 

 in combination with the nucleic acid molecule. In most cases the 

 decomposition does not proceed further in gastric digestion. Through 

 the action of the pancreatic juice, however, the remainder of the 

 protein is split off and the nucleic acid set free. The decomposition 

 of nucleoprotein may be diagramatically expressed thus, although 

 the course of decomposition is probably not quite so simple as indicated. 



1 For review of the literature on nucleic acids and nucleases see Monograph on "Nucleic 

 Acids" by Walter Jones, New York, 1914, Longmans Green & Co. 



123 



