10 CHEMICAL SPECIFICITY OF NUCLEIC ACIDS 



6. METHODS OF HYDROLYSIS 



It has long been known that the purines can be spUt off com- 

 pletely by a relatively mild acid hydrolysis of the nucleic acids. 

 This could be confirmed in our laboratory in a more rigorous 

 manner by the demonstration that heating at 100° for 1 hour in 

 A^ sulfuric acid effects the quantitative liberation of adenine and 

 guanine from adenylic and guanylic acids, respectively. The 

 liberation of the pyrimidines, however, requires much more 

 energetic methods of cleavage. Heating at high temperatures with 

 strong mineral acid under pressure is usually resorted to. To 

 what extent these procedures brought about the destruction of 

 the pyrimidines could not be ascertained previously owing to the 

 lack of suitable analytical procedures. The experiments sum- 

 marized in Table 1, which are quoted from a recent paper^^, 

 show that the extremely robust cleavage methods with mineral 



TABLE 1 



RESISTANCE OF PYRIMIDINES TO TREATMENT WITH STRONG ACID* 



* A mixture of pyrimidines of known concentration was dissolved in the 

 acids indicated below and heated at 175° in a bomb tube. The concen- 

 tration shifts of the individual pyrimidines were determined through a 

 comparison of the recoveries of separated pyrimidines before and after 

 the heating of the mixture. 



acids usually employed must have led to a very considerable 

 degradation of cytosine to uracil. Uracil and also thymine are 



