CHEMICAL SPECIES INDUCED BY X-RAYS IN CELLS 101 



radicals we observe once again into those which can be liarnilessly 

 removed by reacting with nitric oxide bnt are toxic after reaction with 

 oxygen, and those which become toxic or damaged by virtue of their 

 reaction with nitric oxide or with oxygen. 



There are then two ways in which the subdivision of Class III into 

 two components can be viewed, each implying different characteristics 

 of the radicals in question. One is as follows: 



Ilia 



1. In presence of *02* Ra* > Ra02* (toxic) 



2. Removable by heat (Anneal.) Ra' "^ > RaH (not toxic) 



3. Reacts with NO* Ra* > RaON (not toxic) 



Illb 



Not annealable Rb' > Rb02* (toxic) 



Reacts with NO' Rb* > RbON (toxic) 



In this case the radicals Rt,* are not sufficiently mobile to be annealed 

 by heat, or they are in some way shielded from H* atoms, or some other 

 characteristic prevents their annealment, so that they persist and be- 

 come active RO2* or RO' radicals when oxygen is admitted to the 

 system. These very radicals are, however, available to NO* as shown by 

 the ESR data, and if the foregoing statement is true, i.e. if they do 

 become toxic radicals even after high temperature treatment, then the 

 combination Rt,ON must be equally as toxic as Rb02*. Heat treat- 

 ment and NO treatment produce the equivalent results biologically 

 when used alone, and no additive effects of sequential treatments of the 

 two agents has been demonstrated. 



If the above explanation is true, we see a distinction between the two 

 radicals on two counts: one (Ra*) is heat annealable, and the other 

 (Rb*) is not, both being toxic when in the form RO2*; and one (Rb*) is 

 toxic as RON and the other (Ra*) is not. 



Another general possibility is seen by setting up the characteristics 

 of the two radicals as follows : 



Ilia — All toxic when in Ra02* form 



1. Annealable Ra' > RaH (not toxic) 



2. Reacts with NO* Ra* > RaON (not toxic) 



Illb — Not toxic when in Rb02* form 



1. Not annealable, but Rb* > Rb02* (not toxic) 



2. Reacts with NO' Rb* > RbON (not toxic) 



In this scheme, the diff"erences between Ra* and Rb' is that one 

 (Ra') is annealable, the other (Rb*) is not; and only the annealable 



