10 



of the molecule? Well, I feel that the things one has to think about are these: 

 In the first place we have atoms that have lost an electron. The positive attri- 

 bute, it seems to me, cannot possibly stay there, or at least there is no reason 

 why it should. It would be quite natural for the neighboring atom to feed an 

 electron into it, in which case, the plus is now in the next atom, even though the 

 positive charge itself does not move physically. But from the place where it 

 started it can go all the way along these chains and probably does so very rapid- 

 ly. So we have a concept of migration up and down fromi one end to the other. 



We have a specific functional region in the molecule, and let's say that 

 this is attached in some way to the substrate or is hooked on to something else. 

 It won't matter. Let us say that a bond is broken. Suppose I indicate a broken 

 bond at X, The breaking of the bond is my conception of the removal of a va- 

 lence electron by the migrating positive charge. This broken bond will mean 

 that the structure will essentially break here, and the fragment can move off 

 with the material of the substrate, or whatever you like, that is bound to it. In 

 which case, the molecule no longer has its specific configuration and its biolog- 

 ical activity is lost. This is inactivation by a single event and corresponds to 

 the fact that the single event occurs in a place where just that one event is suf- 

 ficient to cause inactivation. This might, for instance, be a prosthetic group 

 that dropped off. The concept I want to state is that of the high energy single 

 event. Let's call that category 1. This, in Augenstine's picture, would be the 

 equivalent of the breaking of an S-S bond. 



Now let's look at something else that can occur. If these positive po- 

 sitions wander around, they can move, for instance, into a place like E and that 

 can mean that for a moment a bond will be broken. Now suppose that for some 

 other reason, e. g. , thermal agitation or another ionization, the bond at D is al- 

 so broken temporarily. Then there can be a motion of the whole end of the 

 chain outward. 



Bear in mind that Figure 1 is not drawn to scale because I have drawn 

 it linearly and, in actual fact, the ends are closer together. It is possible that 

 this outward motion will then cause a cross-linkage between, for example, F 

 and G, and this cross-linkage will make permanent the sort of damage that has 

 occurred. This second method, too, is clearly dependent on the strength of the 

 hydrogen bonding. This is something that may be dependent on temperature. 



I feel that there is a lot of significance to the fact that proteins have a 

 high coefficient of thermal expansion, and this may mean that they contain bonds 

 that are actually Capable of being weakened just by the fact that they are a little 

 further apart when the high expansion is taking place. When this type of inac- 

 tivation involving two bonds takes place, we observe a temperature effect. 



In any event I should like to point out that the migration of the energy 

 up and down these chains may take place by means of nnigralLon of the plus 

 charge; this seems to me to be the significant thing. 



I have concentrated on the plus charge, but what I have said also ap- 

 plies equally well to the minus, which will be stopped in the vicinity of an atom. 

 Of course, in time these opposite charges will come close enough together so 

 that a recombination can occur, and in a period of time of about 10"° seconds 

 recombination will be completed. It must be as small as that or we would not 

 observe time-dose rate reciprocity in radiation action. 



CURTIS: If I can get one thing clear, both of these events really occur 

 at the outside of this molecule. That is, you have a volume here, and if I have 



