CHEIMICAL SPECIES INDUCED BY X-RAYS IN 

 CELLS AND THEIR ROLE IN RADIATION INJURYf 



E. L. POWERS 



Division of Biohxjiad and Medical Research, Argonne National L(d) oratory, 



Argonne, Illinois, U.S.A. 



SUMMARY 



The experimental evidence for the existence of several chemical species in 

 the dry bacterial spore after X-irradiation is reviewed and examined critically. 

 One very short-lived species is recognized only if oxygen is present during the 

 time of irradiation; another becomes toxic anoxically and is recognized only if 

 hydrogen sulphide is present during irradiation. Certain characteristics of the 

 long-lived free radicals that become toxic to the cell if they combine with oxygen 

 are examined with special attention to reconciliation of biological and chemical 

 evidence with jahysical evidence gained from ESR techniques. Post-irradiation 

 thermal annealment and post-irradiation treatment with nitric oxide reduce 

 the biological effectiveness of X-rays to the same degree; but the fonner approx- 

 imately halves ESR signals, whereas the latter removes all signals almost com- 

 pletely. One interpretation of these results is that two general kinds of radicals 

 are formed, one of which is thermally annealable and biologically important 

 the other of which is not. Both react with oxygen and with NO. While the 

 removal of the two kinds of radicals with NO results in obliteration of the ESR 

 signal, the biological result is the same as that seen after thermal annealment 

 because only those radicals are important biologically. Another interpretation is 

 that reaction of one kind of radical with NO results in a harmless complex, whereas 

 reaction with a second kind results in a harmful complex. These studies and 

 others similar to them, especially those involving the role of water in these effects, 

 should lead eventually to some vmderstanding of the early effects of high energy 

 radiations in cells. 



INTRODUCTION 



The "initial" effects of high energy radiations in living systems 

 depend npon the same parameters as those in non-living ones, and any 

 one interested in miderstanding the biological effects of irradiation 

 should find assistance from studies on the interactions between radia- 

 tions and purely physical systems. For instance the relationship be- 

 tween stopping power and atomic number is undoubtedly the same in 

 protoplasm as it is in a plastic, the very early chemical changes (i.e. 

 those strictly non-enzymatic in nature) should not be different, and the 



t This work was performed under the auspices of the United States Atomic Energy 

 Commission, 



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