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WALDO E. COHN 



"standard" material.''^' *'^- ^^ Since the commercially available resins have 

 varied over quite a range of divinylbenzene content, it is not possible to 

 say, with respect to some reported separations, just what degree of cross- 

 linking existed in some of the exchangers used. It is known that the poly- 

 nucleotides of the ribonuclease digest, readily separable up to at least tetra- 

 nucleotides on 2 % divinylbenzene material in a chloride system,^^ were not 

 separated on 10% divinylbenzene resin by chloride;^^ very broad peaks, 



Fig. 18. Separation of the products of ribonuclease digestion of PNA.*' 

 Exchanger: Dowex-l(2% DVB) -chloride, 400 mesh, 15 cm. X 3.7 cm. 2. 

 Solution: HCl + NaCl as follows: I, 0.005 N HCl; II, 0.01 N HCl; III-IX, 0.01 

 iVHCl + 0.0125, 0.025, 0.05, 0.1, 0.2, 0.3, and 1 A^ NaCl, respectively; X, 2 A^HCl. 

 Sorbed material: 700 mg. calf liver PNA -|- 10 mg. ribonuclease in 105 ml. H2O, 

 22 hr. at 37°C., + NaOH as required to keep at pH 7.0; pH lowered to 2.0; chilled; 

 centrifuged; supernatant made alkaline with NH4OH; sorbed. 



indicating a poor degree of equilibration and leading to overlapping of 

 components, were obtained (qualitatively similar results have been reported 

 with polypeptides") . 



h. The Ribonuclease Digest 



An example of the separation of polynucleotides by anion exchange is 

 shown in Fig. 18.'*^ In this separation, the concentration of HCl was held 

 at 0.01 A'' (after a brief sequence at 0.005 A^) with stepwise increments in 

 NaCl to remove the more strongly sorbed polynucleotides. Merrifield and 

 Woolley^" used stronger HCl rather than NaCl to remove polynucleotides 



" C. E. Carter and W. E. Cohn, J. Am. Chem. Soc. 72, 2604 (1950). 

 " S. Moore, personal communication. 



