20 



MAGEE: Aromatics don't give it. 



KAMEN: What happens •? 



PLATZMAN: The excess energy is converted to heat. 



MAGEE: This is a basis for protection theory. It sometimes happens 

 that in a sensitive region, a molecule can dissipate energy that is trapped w^ith- 

 out dissociation, and then you have a protection from radiation. All we need is 

 a recipe for favorable atomic configurations. 



PLATZMAN: I should like to raise the question of the mechanism 

 whereby a single ionization brings about the suggested effect in a protein. What 

 is your opinion of the theory for this that Franck and I advanced (15)? 



POLLARD: You tell me about it, then I will tell you. 



PLATZMAN: It involved the simultaneous breakage and reorganization 

 of many hydrogen bonds as a result of rotation of water dipoles about the freshly 

 formed charge. 



POLLARD: In other words, this occurs the moment water hits it. 

 Being dry, how does this work? 



PLATZMAN: Dry protein still shows strong dielectric absorption; 

 therefore, it contains groups that reorient under the influence of electric fields. 

 This reorientation is, without question, associated with the hydrogen bonds, and 

 the sudden production of an electric charge within the protein must cause the 

 breakage of many hydrogen bonds over a great region. Subsequent reforming of 

 the bonds would then be irregular and might not give the original configuration. 



POLLARD: I think Hutchinson does not like this. Now I am a little 

 out of my department, at the moment, but Hutchinson's low voltage electron ex- 

 periments are really very informative about this (11). What you find is that you 

 don't get a really large effect on a molecule like bovine serum albumin until you 

 get up to about 15 electron volts, indicating that you do have to get ionization 

 first. You can put a great many electrons into your bovine serum albumin, so 

 that it is certainly getting considerable charge; this does not seem to me, how- 

 ever, to be reorienting hydrogen bonds and producing an effect. 



PLATZMAN: It would have to be pretty carefully proven that electrons 

 get in. 



POLLARD: That is right. I don't want to be dogmatic about this, and 

 it would be better if he were sure that the electrons are in there. He is not, of 

 course, but he says this is an indication. A figure of 15 is a sort of plausible 

 broad ionization figure. I think these low voltage electron experiments are very 

 informative. Obviously, they should be done on a larger scale so that we get 

 data more quickly. 



Could I go on for another couple of minutes, putting in the seamy side 

 of this? I want to say why I think this is important first. In considering a cell 

 that has a nucleus, chromosomes, mitochondria and so forth, distributed through 

 it, one fact that must be borne in mind is that radiation that occurs within the 

 molecular region will produce a certain effect. We like to say that you can make 

 a fairly good estimate of the proportion of radiation damage that will occur as a 

 result of this direct process by simply taking the total volume of every one of 



