404 



RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



characterized, is similar to yeast nucleic acid except that 2-desoxyribose 

 and thymine are substituted for ribose and uracil, respectively. Ion- 

 exchange chromatography of the nucleic acids has been reviewed by Cohn 

 (28) and Samuelson (2). 



The nucleotides may be retained by anion exchangers above pH fi 

 where the phosphate group is functional, or by cation exchangers in the 

 low pH region where the amino group tends to adsorb. Anion exchange 

 appears to be the more effective. Both cation and anion exchange can 



0.7 



0-6 



Start 0.002 N HCI 

 -Bases and Ribosides 



0.5 



E 

 o 



04 



03 



02 



/' 



Cytidylic Acid 



R, 



Start 

 0.003 N 

 HCI 



Adenylic Acids 

 a b 



A 



. Uridytic Acid 



\ 



^J 



1 



1.5 



3.0 



3.5 



0.5 1.0 1.5 



Volume eluting solution, liters 



Fia. 9-11. Demonstration of isomers in the separation of mononucleotides of rat liver 

 ribonucleic acid by anion exchange. Exchanger: Dowex 1, 12.5 cm by 0.74 cm-. Test 

 material: about 14 mg of mixed nucleotides from Ba(OH)o hydrolysis of rat liver 

 nucleic acid, in 10 ml H2O. {From W . E. Cohn, The Anion-exchange Separation of 

 Ribonucleotides, J. Am. Chem. Soc., 72: 1471-1478 (1950).] 



be used for separation of the nucleosides as well as of the purine and 

 pyrimidine bases. The details of separations accomplished may be noted 

 in Table 9-5, compiled from (28). In addition to the discovery of new 

 nucleotides, an outstanding contribution has been the unequivocal dem- 

 onstration of the existence of isomers. Figure 9-11 illustrates the appear- 

 ance and resolution of isomers of adenylic acid and of guanylic acid from 

 rat liver ribonucleic acid after passage through an anion exchanger (29). 

 Other experiments have confirmed this interpretation. Methods have 

 also been described for separation of the adenosine phosphates. 



Estimation of Total Salt Concentration. After passage of a neutral 

 solution containing several salts through a hydrogen-ion exchanger, the 



