228 



WALDO E. COHN 



URIDYLIC ACIDS 



LITERS THROUGH COLUMNS 



Fig. 11. Separation of (a) cytidylic and (b) uridylic acids by anion exchange.'' 

 Exchanger: Dowex-1 -acetate (a), -formate (b), 200-400 mesh, (a) 11.3 cm. X 

 0.86 cm.^ (b) 9.5 cm. X 0.76 cm.^. 



Solutions: (a) 0.025 M HAc + 0.025 M NaAc, (b) 0.04 M Na formate + 0.0004 

 M formic acid. 



Sorbed materials: (a) crude deoxycytidylic acid fraction"' '" (see Fig. 9), con- 

 taining deoxy-5-methylcytidylic acid (shown as "X"), plus cytidylic acids a and 

 b (2' and 3') ; (b) uridylic acids a and b (2' and 3')- 



of cytidylic acid. Similar separations are achieved in 0.01 A^ formic acid. 

 In Fig. lib is demonstrated the separation of the 2' and 3' isomers of 

 uridylic acid in a formate system. These are not well separated in acid 

 systems. 



(4) Adenylic and Inosinic Acids. The 5'-, 2'-, and 3'-phosphate isomers 

 of adenosine are easily separable by 0.002 A'' HCP®' 2^' ^^ or by 0.1 M formic 

 acid.'^' *° (A separation at pH 5.5 in a chloride system has also been de- 

 scribed,^'* At this pH, the inosinic acid isomers, included in the experiment, 

 precede the corresponding adenylic acids just as do the uridylic acids; 

 see Fig. 12.) Fig. 13 shows the separation of a partially deaminated mixture 

 of the three adenylic acids by formic acid. 



(5) UridyUc Acids. It will be noted that the inosinic acids not only follow 

 the adenylic acids at a considerable distance but are not well separated 

 by formic acid. The uridylic acids show the same behavior (see Fig. 5^'). 

 Hence, in practice, resort has been made, for the separation of uridylic acid 

 isomers after the removal of the cytidylic and adenylic acids, to buffer 

 systems of higher pH and ionic strength (see Fig. 11). This also avoids 

 entangling the uridylic acids with the guanylic acids; it will be recalled 

 (see Fig. 7) that these two groups are not well separated at low pH. 



(6) Guanylic Acids. The guanylic acid isomers separate well at all pH 

 values tested. Separations at pH 2.5 (HCl) and 5 (formate) have been re- 

 ported,^'' ^^ both as part of the analysis of an alkaline digest of PNA which 

 includes the four isomeric pairs of nucleotides. 



