396 B. MAGASANIK 



The results reported in the subsequent sections were calculated using these values. 



Method S.2* Hydrolysis of PNA by dilute alkali to a mixture of mononucleotides, 

 separation of the mixture by chromatography on a basic ion-exchange resin (Dowex 

 1) [compare Cohn, Chapter 6], elution with acid, and spectrophotometric estimation. 

 In this method the 2'- and 3'-phosphates of the purine nucleosides, which are formed 

 by the action of alkali, are separated. The results recorded here give the sum of the 

 2'- and 3'-phosphates of adenine or guanine. 



Method 4-^'^- *' Hydrolysis of PNA by dilute alkali, followed by separation of the 

 mixture of mononucleotides by electrophoresis on filter paper, elution, and spectro- 

 photometric estimation or phosphorus analysis. [Cf. Smith, Chapter 8.] 



Method 5.**' ®^ Hydrolysis of PNA by N H2SO4 to a mixture of purines and pyrimi- 

 dine nucleotides. The purines are precipitated as insoluble silver salts; these are de- 

 composed by hydrochloric acid, and the concentration of adenine and of guanine in 

 the supernatant solution determined by measurement of its ultraviolet extinction at 

 two wavelengths. The concentrations of the pyrimidine nucleotides in the super- 

 natant solution of the purine silver salts are similarly determined. Alternatively the 

 pyrimidine nucleotides may be converted to nucleosides by treatment with prostatic 

 phosphatase prior to spectrophotometric estimation. [Compare also Loring, Chapter 

 5.] 



Methods 1, 3, and 4 permit the separation of the four nucleic acid com- 

 ponents and are therefore presumably superior in accuracy to methods 2 

 and 5. The recovery of pyrimidine nucleotides in method 1 may be low, 

 even when the correction described by the authors is applied. ^^ 



In general the reliability of a method is judged by the completeness with 

 which the sum of the products obtained will account for the phosphorus 

 and nitrogen content of the PNA preparation. The methods described 

 allow 90-100 % of the nitrogen and the phosphorus content to be accounted 

 for as bases or nucleotides. Usually the composition of the PNA sample is 

 presented as the fraction of PNA phosphorus accounted for in each nucleo- 

 tide. However, in order to facilitate the comparison of the composition of 

 different PNA preparations it is advantageous to express the results as 

 the molar ratios of the nucleotides relative to adenine as 10.** It is in this 

 manner that the composition of PNA preparations is presented in the 

 succeeding sections. 



3. PNA FROM Animal Tissues 



A sufficiently large number of animal PNA preparations has been isolated 

 and analyzed to permit consideration of the cjuestion whether animal 

 pentose nucleic acids are species-specific or organ -specific or fall into no 

 clearly discernible pattern. The composition of PNA preparations isolated 



«2 J. N. Davidson and R. M. S. Smellie, Biochem. J. 52, 594 (1952). 

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

 6^ S. E. Kerr, K. Seraidarian, and M. Wargon, J. Biol. Chem. 181, 761 (1949). 

 " H. S. Loring, J. L. Fairley, H. W. Bortner, and H. L. Seagran, J. Biol. Chem. 197, 

 809 (1952). 



