348 



ERWIN CHARGAFF 



TABLE IV 



Liberation of Adenine from Sodium Deoxypentose Nucleate of 

 Wheat Germ and from Enzymically Produced "Cores" 



ease by A^ H2SO4, formic acid,^^^ and perchloric acid;^^* the other type, the 

 concentration of which is considerably increased in the nondiffusible "cores" 

 (see Section V.3), appears resistant to sulfuric acid, but not to the other 

 agents (see Table IV). In other words, a small proportion of the total 

 adenylic acid contained in this nucleic acid shows the resistance to cleavage 

 by mineral acid at 100° that is characteristic of the pyrimidine nucleotides. 

 Similar, though not equally striking, observations have been made in the 

 other instances cited above. It is not probable that they have to do with 

 the type of phosphate bridges linking the nucleosides in the deoxypentose 

 nucleic acids which presumably are 3': 5' in most cases, though exceptions 

 may occur. [See Chapter 12.] This stability is more likely connected with 

 the glycosidic bond (e.g., sugar at position 1 or 3 of the purine). But this 

 is, for the moment, only speculation. 



VII. Composition of Deoxypentose Nucleic Acids 



1. General 



The study of the constitution and structure of a complicated cell con- 

 stituent of a high molecular weight, such as a protein, a polysaccharide or 

 a nucleic acid, goes through several well-defined stages. First, the substance 

 must be properly recognized and also distinguished from other compounds 

 with which it may share some, but not the decisive, properties. Next, all 

 its ultimate organic constituents — and it may comprise one variety or 

 many^ — ^have to be described in a qualitative fashion. As regards the nucleic 

 acids, no better account of these two stages will be found than that given 

 by Levene.^ Rut when quantity has to be translated into quality, when 

 discrimination has to be made not between substances that are palpably 

 different, but between those that are seemingly identical, the task becomes 



2« E. Vischer and E. Chargaff, J. Biol. Chem. 176, 715 (1948). 



