62 



J. A. V. Butler 



and liberation of inorganic phosphate; (5) occurs normally 

 as a consequence of (4) (Scholes and Weiss, 1952; Butler and 

 Conway, 1953). 



All these chemical effects are primarily radical reactions 

 and can be produced by — OH radicals formed in other ways. 

 The reactions of — H are not so well defined, except in so 



o 



X 



a 



o 



NO IRRADIATION 

 I X 10 £ IN SOLUTION 

 2xl0^r IN SOLUTION 

 8x lO^r IN SOLID 

 |-2xl0^r SOLUTION 



2 3 4 



HOURS HYDROLYSIS 



— p- 



6 



Fig. 3. Hydrolysis of DNA by heating with sulphuric acid 

 after irradiation (Butler and Simson, 1954). 



far as it combines with oxygen to form the oxidizing radical 

 OgH. The liberation of inorganic phosphate varies with the 

 square of the dose, as is to be expected since two phosphate 

 ester bonds have to be broken in order to liberate PO4 

 (Butler and Conway, 1953). It is not easy to demonstrate 

 directly the breakage of the nucleotide chains. The effect of 

 single breakage is to liberate a terminal phosphate group, but 

 it can be shown that after irradiation free phosphate is more 

 quickly liberated on acid hydrolysis (Butler and Simson, 

 1954; see also Fig. 3). 



