94 



Fano's argument regarding distribution of excitation energy. It is just the thing 

 that I think does not apply to the kind of molecules which Dr. Linschitz dis- 

 cussed. I did a little rough calculation and it seems to me that there are levels 

 which are more often from 6 to 20 volts. Those levels in a molecule like this 

 are essentially mutually interacting and anything you do up at 20 volts is going 

 eventually to come down to 5, 6 or 7 volts and cause the photochemical effects 

 which Dr. Linschitz discussed. 



POLLARD: How did you get up to 20 volts? 



KASHA: Well, I think Dr. Fano was talking about something happening at 20 

 volts from some higher energy radiation. 



FANO: This funneling of energy into particular kinds of excitation is some- 

 thing that happens in materials which really have special kinds of structures, so 

 that they are fluorescent. Fluorescent materials are the object of much study 

 just because it is convenient to use them. But there is not much evidence that 

 most of the biological tissues are like that. Most of the organic materials do not 

 have appreciable atomic groupings with such special structure. 



MAZIA: Couldn't this problem be approached experimentally by comparing 

 the effects of ultraviolet and ionizing radiations in cases where you have a qual- 

 itatively distinguishable effect? For instance, you spoke of absorption in the 

 ultraviolet by nucleic acid. If you irradiate nucleic acid with ultraviolet, the ef- 

 fects on its structure are detectable by losses in ultraviolet absorption. How 

 heavily would you have to irradiate nucleic acid with ionizing radiation to detect 

 these same changes? Have you ever picked them up? 



POLLARD: Pretty heavily, I would say, to pick up an effect that way. But 

 to lose the biological function -- 



MAZIA: I was referring definitely to Dr. Fano's question. If the energy had 

 to be funneled in through the mechanism he was discussing would you be able to 

 detect the same kind of effect with ionizing radiation? 



POLLARD: You certainly don't. The striking thing about irradiating stuff 

 this way is that you don't see any change until you put it in solution. The only 

 thing we have done on this for the two cases where we had bovine serum albumin 

 and hemoglobin. We have put them on a quartz slide, and we have examined 

 them in the Beckmann apparatus. It is really very surprising how small the 

 change is in all the absorption bands and yet such material is totally insoluble. 

 As soon as you do shake it up and look at it a little in solution all the absorbing 

 bands have changed. Here I am talking in a certain sense against myself. You 

 can have a process which is happening in the inert molecule. It is when the 

 molecule is called on to function that you notice the difference, and the first 

 function it has to survive is the ability of going into solution or at least standing 

 contact with water. If you simply irradiated a nucleic acid molecule in the dry 

 state you would have to put tremendous amounts of energy in to see these effects. 



KAMEN: Perhaps the most spectacular demonstration of the difference be- 

 tween low energy ultraviolet radiation and ionizing radiation is that of the photo- 

 reactivation of phage. If you deactivate phage with ultraviolet you can reactivate 

 it with visible light. 



POLLARD: Well, that is in the bacterium, don't forget that. 



KAMEN: Yes, that is a most important thing to remember. If you irradiate 



