12 



one thing that may be very significant in radiation action is any type of bonding in 

 which this is unlikely to happen. Another thing I feel may be very significant, is 

 the ring structure in which this, so to speak, is held up by just going around and 

 around the ring for a while and, therefore, not traveling. 



PLATZMAN: What is important about postulating that? 



POLLARD: The important thing is for this type of broken bond, as I 

 see it, to be able to migrate. 



PLATZMAN: Why is that important? 



POLLARD: So as to have an event anywhere in the molecule apparently 

 produce an inactivation. 



There are two points of view on this. One is that a protein molecule is 

 so sensitive that anywhere you hit it, it dies. I look on that as being a little su- 

 perstitious. I just don't think any biological system is quite that critical. I used 

 to feel that way, but I no longer do. If that is not so, then you have to say the 

 protein will cease to function biologically under a condition in which a bond is 

 broken and the wrong bond is formed. The place where a bond can be broken and 

 a wrong bond can form isn't just anywhere in the molecule. Apparently it does 

 not matter where we put the radiation energy in; we are able to find the place 

 where the bond is broken and the wrong bond is formed. So I feel there has to be 

 some nneans for the migration of this effect. 



PLATZMAN: But perhaps not with 100 percent efficiency. 



POLLARD: No, not with 100 percent efficiency; in fact, almost surely 

 this is not 100 percent because we now find molecules which require at least 3 

 ionizations to inactivate them. Not 1 but 3, and that alone means that there is an 

 efficiency factor. 



It certainly did not seem obvious to me that because you "ionize" an 

 atom in a solid molecular configuration like this, that that particular atom had to 

 stay ionized. It would seem to me that it would be just the other way around and 

 there would be every reason for the place of ionization to have a statistical 

 chance of moving all around. 



BARRON: You are acquainted with our work in which we irradiated 

 enzymes containing the sulfnydryl groups as the active group and where the only 

 thing that happened was the oxidation of the SH group without destruction of the 

 protein molecule. That is completely reversible because you can reduce the SH 

 group and enzyme activity is restored. There, you see, you cannot use your 

 criteria for explaining inactivation of the enzyme. 



POLLARD: No, that is a chemical reaction. 



BARRON: That is correct. I am very glad that Dr. Pollard is talking 

 about the direct theory, but we have to make sure that what he is talking about 

 has nothing to do with the indirect action. 



POLLARD: That is right. 



PLATZMAN: Is someone going to tell us just how good a distinction 

 one can make between direct and indirect action "^ 



