CHAPTER VI 

 NUCLEIC ACIDS AND NTJCLEOPROTEINS 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 addi- 

 tion of acetic acid in excess of which they dissolve with more or less 

 difficulty although readily soluble in excess of 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 

 are probably in many cases to be considered as mixtures of protein and 

 nucleic acid rather than as definite compounds. Under the ac- 

 tion 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 decom- 

 position 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 nucleo- 

 protein may be diagrammatically 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 nucleuses see Monograph on "Nucleic 

 Acids" by Walter Jones, New York, 1920, Longmans Green & Co. 



