ELECTROPHORETIC SEPARATION OF NUCLEIC ACID COMPONENTS 283 



4. Separation of Nucleosides and Nucleotides as Borate 



Complexes 



Under certain conditions sugars will form complexes with boric acid 

 believed to be of the types I, 11, and III. 



— C— O 



— C— O 

 I 



I 



B— OH 



C— O OH 



\ / 

 B 



/ \ 

 C— O OH 



I 



II 



H+ 



— C— O 



— C— O 



O— C— 



O— C— 



H+ 



III 



Types II and III are only formed when two adjacent cis-hydroxyls are 

 present in the sugar ring, and, in dilute solutions, when the relative pro- 

 portions of borate to sugar are high, type II predominates.-* It is thus 

 possible by borate complex formation to introduce a new dissociating acid 

 group into sugar residues possessing two m-hydroxyl groups. 



The nucleic acid components bearing czV(OH) groups are ribose (which 

 in the pyranose form has four), and ribonucleosides, ribonucleoside-5'- 

 phosphates, and dinucleoside monophosphates from PNA (in the 2'- and 

 3 '-positions). Jaenicke and Vollbrechtshausen^^ have made use of borate 

 complex formation in the separation of some nucleosides and nucleotides 

 by electrophoresis in 0.1 ilf borate buffer pH 9.2. The pK of the first dissoci- 

 ation of boric acid is 9.0, so that at this pH the acidic group of the complex 

 is partially dissociated and the ribonucleoside-5 '-phosphates bear an ad- 

 ditional net charge and, therefore, move faster than other nucleotides. 

 Under these conditions the ribonucleosides move towards the anode in the 

 order (of increasing mobility): adenosine, guanosine and cytidine, uridine; 

 the rate of movement presumably being determined by the negative charges 

 due to the borate complex and those on the enol (OH) groups of the bases. 

 The deoxy ribonucleosides which only carry charges on the partially dis- 

 sociated enol (OH) groups move more slowly than the ribonucleosides. 



" H. S. Isbell, J. F. Brewster, N. B. Holt, and H. L. Frush, J. Research Natl. Bur. 



Standards iO, 129 (1948). 

 2' L. Jaenicke and I. Vollbrechtshausen, N aturwissenschaflen 39, 86 (1952). 



