ELECTROPHORETIC SEPARATION OF NUCLEIC ACID COMPONENTS 269 



TABLE I 

 The Dissociation Constants of Some Purines, Pyrimidines, Nucleosides, and 



Nucleotides" 



" The values given under the headings adenylic, guanylic, cytidylic, and uridylic acids' were probably 

 determined on mixtures of the 2' and 3'-phosphates. The amino group pK given for adenosine-5'-phosphate» 

 does not bear the expected relation to that of the mixture of adenosine-2'- and -3'-phosphates and may be 

 incorrect. 



3.5 where the degree of dissociation of the NH2 group of adenyUc acid is 

 0.54, giianyhc acid 0.05, cytidylic acid 0.84, while uridylic acid of course 

 has none. As each nucleotide carries a negative charge of 1 due to the pri- 

 mary phosphate group, the net negative charges are: adenylic acid 0.46, 

 guanylic acid 0.95, cytidylic acid 0.16, and uridylic acid 1.00. The four 

 mononucleotides have very nearly the same size and so approximately the 

 same resistance to motion; consequently these figures give their relative 

 mobilities at this pH. With the use of the dissociation curves the relative 

 mobilities of the nucleotides may be calculated for any other pH. 



The pK values of the amino groups of the isomeric nucleoside-2'-, -3'-, 

 and -5 '-phosphates differ so little that they would only be expected to show 

 separation in a long electrophoretic mn and in practice generally run to- 

 gether, although Davidson et at? • * have observed incomplete separation 

 of guanosine-2'- and -3 '-phosphates at pH 3.5. 



^ H. Wassermeyer, Z. physiol. Chern. 179, 238 (1928). 



« L. F. Cavalieri, J. Am. Chem. Soc. 74, 5804 (1952). 



■' J. N. Davidson and R. M. S. Smellie, Biochem. J. 52, 599 (1952). 



« G. W. Crosbie, R. M. S. Smellie, and J. N. Davidson, Biochem. J. 54, 287 (1953). 



