INITIAL RADIATION DAMAGE AT SUB-CELLULAR LEVEL 19 



ALEXANDER: Particularly larp;e changos ocfur when air is admitted. On heating 

 the changes are less consitlerable. When irradiation was performed at room tem- 

 perature different changes of the signals were also provided. I cannot go into the 

 details but would like to emphasize the importance of our results in determining 

 the role of sulphiu*. 



POWERS: T do not think that these data support yovir surmises on the role of 

 sulphur. 



ALEXANDER : When ii-radiation was carried out in the presence of oxygen, ESR 

 signals of the irradiated cysteine and proteins were similar, but if during irradia- 

 tion oxygen was lacking, the cysteine and protein signals differed. We believe 

 that the similarity of these signals is due to the oxygen, in the presence of which 

 peroxide radicals are formed. 



LEBEDiNSKY : What experimental data confirm the very valuable, in my oj)inion, 

 sviggestion about the importance of the membrane permeability disturbances? 



ALEXANDER : I hope to demonstrate this in the future by excluding other possible 

 causes, since it would hardly be possible to obtain direct proof. Besides this, it is 

 probably possible to get physiological and biochemical data confirming this view- 

 point in an indirect way. But I have no direct evidence except the fact that 

 following irradiation of erythrocytes with several hundred roentgens a leakage 

 of the potassium is observed while at the same time we have shown that there 

 is a change of the surface potential following such a dose. However, this is only 

 a suggestion, not a proof. 



BLUMENFELD : What could you say about the form, width and position of the 

 ESR signals which you obtain from protein at liquid nitrogen temperature? 



ALEXANDER: We did not obtain ESR signals with unirradiated protein whether 

 this was denatiu'ed or native. 



