38 



o 



is irradiated, the optical density at 2600 A decreases by 0.09. Addition of 



ribose to form adenosine (9-S-D-ribofurano-sidoadenine), 



N 



CH ^ Ov CH^OH 



. N ^ C ' • C 



'^C — C^ ' 



H ' ' H 



OH OH 



decreases by half the sensitivity of the compound. Further protection against 

 the effect of X irradiation is observed on addition of phosphoric acid residues. 

 The ionic yields of several of these compounds is given in Table IV. It can be 

 seen that while the ionic yields of thymine, uracil, cytosine, adenine, and 

 guanine are around 1 per 100 ev. , they are considerably less for ribonucleic 

 and desoxyribonucleic acids. 



TABLE IV 



RADIOCHEMICAL YIELD ON X IRRADIATION OF 

 PURINES AND PYRIMIDINES IRRADIATED IN 

 DILUTED AQUEOUS SOLUTIONS 



Substance G(100ev.) 



CARTER: The latter are more stable as measured by one criterion'' 



BARRON: That is correct; stable around the chromophore groups 

 responsible for light absorption in the ultraviolet. 



CHARGAFF: How do you explain the difference between thymine and 

 guanine'? 



