238 



THE EFFECT OF IONIZING RADIATIONS 



unaffected, the O2 uptake in the presence of acetate, glutamate, aspar- 

 tate, lactate, and allantoin was depressed (Table 5). Pyruvate and 

 succinate oxidation was not affected. When irradiation of bacteria was 

 performed in the absence of oxygen, the inhibition of acetate oxidation 

 diminished, evidence that the radiation effect was due to an oxidation 

 process. 



TABLE 5 



Effect of X-Rays on Some Oxidations Produced by Corynebaderium 

 creatinovorans (Washed Bacteria) 



(Unpublished experiments) 



Although we are still far from the desired goal — clear understanding 

 of the mechanism of ionizing radiations in biological systems — I feel 

 that we have made substantial progress. The preponderant role of 

 water and of oxygen has been firmly established. This is obvious in a 

 system like the living cell, containing 80 per cent of water saturated 

 with oxygen. Furthermore, it has also been established that oxidation 

 reactions dominate the picture, oxidations produced mainly by the 

 powerful oxidizing radicals OH and O2H, and less effectively by H2O2 

 produced on reduction of O2H. There are good arguments to postulate 

 that, of these oxidations, the oxidation of thiol groups, in particular, is 

 of considerable importance because of the multiple functions of these 

 groups in cell metabolism, in cell division, in cell growth. Work in 

 progress on the effect of ionizing radiations on other systems of bio- 

 logical importance will further clarify the problem. 



It must be emphasized, however, that all these studies on the effect 

 of ionizing radiations on systems of biological importance are only a 

 guide — an essential guide — for the search of effects in the living cell. 

 These studies represent somewhat like thermodynamic possibilities. If 

 a biologic system is found to be very sensitive, it is possible that the 

 same changes might occur in the living cell; it may also be possible 

 that such might not be the case because of the presence of other factors 



