DNA AND Effects of Radiation and Peroxides 287 



Maxwell found that X-irradiation also part-inactivates the 

 larger T-even phages of the T series. Working with purified 

 T4, he has studied the inactivation by ascorbic acid of phage 

 pretreated by peroxides. 



Succinic peroxide, although inactivating the phage, failed 

 to produce part-inactivated particles. In contrast, however, 

 cumene peroxide was found to produce part-inactivated 

 phage. Concentrated phage T4 was treated for 5 minutes 

 with 10"^ cumene peroxide, which produces about 50 percent 

 inactivation. The phage was then diluted to stop further 

 action of the peroxide, and then treated with 10 ~^ M-ascorbic 

 acid. Fig. 4 shows that the rate of inactivation of the pre- 

 treated phage is greater than that of normal T4. 



It is of interest that cumene peroxide produces (while 

 succinic peroxide does not) a very typical change; ionizing 

 radiation also produces this change when acting under con- 

 ditions of indirect efPect. Experiments currently being carried 

 out by Dr. Maxwell seem to indicate that most of the part- 

 inactivation is due to a change occurring in the DNA, although 

 there may be a slight effect on the tail. 



Mutagenicity of succinic peroxide 



Mutagenic effects by some organic peroxides have been 

 observed in Neurospora by Dickey, Cleland and Lotz (1949). 

 Moreover, mutagenicity of some irradiated organic media can 

 be attributed to long-lived radioformed organic peroxides 

 (Wyss et al., 1950). Preliminary experiments carried out with 

 succinic peroxide indicate that such mutagenic activity cannot 

 be observed with all peroxides nor necessarily in all biological 

 systems. 



(a) Dr. R. F. Kimball (1955, personal communication), of 

 Oak Ridge, exposed Paramecia to peroxide for 10 minutes 

 at 26° C in the dark. Following exposure, individual Paramecia 

 were isolated and several days later, groups of 25 autogamous 

 animals were isolated from each treated animal. Those 

 exautogamous clones which reached a maximum population 



