92 NUCLEIC ACIDS AND NUCLEOPROTEINS 



pyrimidine derivatives that were flanked on both sides by purine 

 nucleotides, whereas more prolonged treatment affects poly- 

 pyrimidine stretches, with the glycoside fission of cytidine more 

 readily brought about than that of thymidine. It was possible to 

 develop methods for the quantitative estimation of the diphos- 

 phates and other small fragments of degradation. Table 22 gives 

 a selection of some of the results. It is clear that this sort of study 

 may be a powerful tool in bringing out variations in the nucleo- 

 tide arrangement of different nucleic acids; it is possible to 

 distinguish between specimens that cannot be distinguished by 

 the total analysis of their constituents. It may be concluded that 

 the nucleic acids listed in Table 22 represented chains consisting 

 predominantly of polypurine and polypyrimidine units and that 

 the arrangement of constituents was far from random. 



5. PENTOSE NUCLEIC ACIDS AND NUCLEOPROTEINS 



In glancing, more briefly, at the composition of various pentose 

 nucleic acids^^ one has to state that nothing much could have 

 been stated as long as isolated preparations were compared. The 



TABLE 22 



DEOXYCYTIDINE AND THYMIDINE 3 ',5 '-DIPHOSPHATES FROM DNA* 



<^0.65 ^0.7 ^t Oq.Io ^1.0 ^''2.6 



Molar ra^io^in DNA ^ ^^ ^ ^^ ^3^ ^ ^^ ^ ^^ ^ ^3 



mole%'o?totalT 23.5 12.8 15.4 15.9 19.9 16.0 



pCp** 

 mole % of total C 



Molar ratio 

 pTp/pCp 



10.8 6.00 9.70 9.20 6.30 14.0 



2.24 2.68 2.16 2.58 4.77 1.80 



* 30 min, 100°, 0.1 M H2SO4; DNA preparations from ox = O, man = 

 M, Arbacia = Ar. Subscripts: t = total DNA; the others indicate NaCl 

 molarity at which fraction was obtained. 

 ** pTp and pCp denote the 3 ',5 '-diphosphates of thymidine and cytidine. 



