270 



J. D. SMITH 



It might be thought that a mononucleotide and the corresponding di- 

 nucleotide, which below pH 5 has twice the charge and approximately 

 twice the size, would not differ in electrophoretic mobihty. This is not the 



Adenylic acid 



4 5 



pH 



Fig. 1. The dissociation curves of the ionizing groups of adenylic, guanylic, cytidy- 

 lic, and uridylic acids plotted from the data of Levene and Simms.* 



case, for the separation of polynucleotides depends on the relative resist- 

 ances to motion of a mononucleotide, its dimer, trimer, etc. Before at- 

 tempting the electrophoretic separation of polynucleotides, Markham and 

 Smith^ ' ^o calculated the probable limits that could be set to the relative 

 resistance to motion of a mononucleotide and its dimer. From its diffusion 



9 R. Markham and J. D. Smith, Nature 168, 406 (1951). 

 1" R. Markham and J. D. Smith, Biochem. J. 52, 558 (1952). 



