202 HUBERT S. LORING 



Guanine 



262-280 mil, C = ; 262-240 m/i, C = 



Total purine 



5.11 X 10^ ' 8.25 X 10^ 



252 mM, C = -^^ ; 276 m^, C = — - 

 10,950 ' ^' 7,120 



The corresponding equations for cytidine and uridine at 260 and 278 m/x 

 and for total pyrimidine nucleosides at 266.5 m/u are as follows: 



Cytidine, C = 

 Uridine, C = 



9.902)278 - 4.50D260 

 1.0 X 10' 



13.01)260 - 6.34D278 

 1.0 X 10« 



■D266.5 



Total pyrimidine nucleoside, C = 



9,380 



2. Effect of Various Treatments on the Recovery of the Purine 



Bases and the Pyrimidine Nucleotides 



Various recovery experiments have been performed to determine the extent to 

 which known crystalline samples of adenine, guanine, cytidylic acid, and uridylic 

 acid could be recovered after treatment by the various procedures outlined above. 

 The percentage recoveries of mixtures of adenine and guanine after precipitation as 

 silver salts, after heating for 1 hour at 100° in 1 A'' H2SO4 and after a combination of 

 the two procedures are shown in Table I. In the same table the recoveries of cytidylic 

 and uridylic acids as cytidine and uridine, respectively, are shown after dephos- 

 phorylation by prostatic phosphatase and after acid hydrolysis and dephosphoryl- 

 ation both without and with the addition and removal of Ag+. Because the re- 

 covery of cytidylic acid is low (96-97%) and the recovery of uridjdic acid high 

 (102-104%) after acid hydrolysis, it appears that, as with cytidine under similar con- 

 ditions, ^^ a 3-4% deamination of cytidylic acid occurs after heating a mixture of these 

 substances in 1 A^ H2SO4 at 100° for 1 hour. Other recovery experiments on mixtures 

 of both purine bases and pyrimidine nucleotides gave similar recoveries ranging from 

 98-101% of the amounts used, provided a correction for 3.5% deamination of cytidylic 

 acid was made. It was furthermore shown that the pyrimidine nucleoside fraction 

 could be filtered through Dowex 1 bicarbonate without loss and that added aromatic 

 amino acids and the traces of purine bases remaining owing to the slight solubility 

 of the silver purines were effectively removed by this treatment. 



3. Experimental Procedure for the Analysis of Ribonucleic Acids 



BY Absorption Spectrophotometry 



In analyzing PNA samples by the above-mentioned procedures, it is desirable to 

 relate the purine and pyrimidine composition to their nitrogen and phosphorus con- 

 tents. In the procedure described below, the Ma and Zuazaga method^^ for nitrogen 

 (micro-Kjeldahl) and a modified Fiske-Subbarow procedure^' were used. 



" T. S. Ma and G. Zuazago, Ind. Eng. Chem., Anal. Ed. 14, 280 (1942). 



