y. A. V. BUTLER AND P. SIMSON 



oxidation of the sugar moiety, resulting in a greater ease of hydrolysis of the 

 phosphate, or (c) the hydrolysis of terminal phosphate which has been 

 produced by the primary action of the radiation. 



; - <? s 



Time of hydrolysis with O-SW^W^^^ 



Figure 1 





However, it is not certain that the viscosity after-effect can be ascribed 

 to the same process as gives rise to hydrolysable phosphate, as very little 

 change in the amount of free phosphate occurs on standing in neutral solu- 

 tions, even after massive doses of X-rays, although the acid treatment can 

 liberate considerable amounts, as shown in Table I. 



Table I 



DNA initial 



DNA after irradiation with 200,000 r 



Same after 16 hr standing . . 



PO4 (y per ml.) 



Sante after 1 hr 

 hydrolysis with H2SO4 



0-28 

 1-68 

 1-80 



A marked change of viscosity may, of course, be brought about b\- the 

 breakage of comparatively few bonds. 



In order to exclude the possible hydrolysis of terminal phosphate, experi- 

 ments were made with the ribonucleotides (not deoxy), adenosine-2' (or 

 3') -phosphate and adenosine-5'-phosphate. The phosphate group of the 

 former compound is easily hydrolysed by sulphuric acid (70°) but that of 

 the 5'-phosphate is barely affected in 1 hour. Treatment of the latter 

 compound with X-rays, or with hydroxyl radicals photochemically gener- 

 ated by ultraviolet light on HgOg, causes a marked increase in the amount 

 of phosphate hydrolysed by sulphuric acid. 



It thus appears that the effect of X-ra>s is to increase the hydrolysability 

 of phosphate which is initially terminal. The actual increase of hydrolysable 



47 



