43 



besides the free radicals from water, free radicals from the ionization of the 

 innumerable substances that are in the cell, and they are going to contribute to 

 the overall effect. 



CARTER: I would certainly agree with Dr. Barron in his interpreta- 

 tion in this regard. I believe, on the basis of prejudice more than anything else, 

 that the primary events probably are concerned with the smaller molecular 

 weight components and those that are exquisitely sensitive to ionizing radiation. 

 These may transmit their effects to the higher molecular weight components. 

 The point that I was arguing (and I believe Dr. Mazia was) was that these high 

 molecular weight structures are quite sensitive; that they do have parameters of 

 structure that probably we don't quite know how to explore at this time and how 

 to correlate with biological activity, but insofar as we can make estimations at 

 this stage of the game, they do seem to be sensitive. 



BARRON: I want to recall for you the experiment with DPN, I have 

 irradiated DPN with 100, 000 r and it has been impossible to produce reduction 

 to DPNH. But when I irradiated with 35, 000 r in the presence of lactic acid, 

 there was a reduction of DPN produced by the oxidation product of lactic acid. 

 This is the sort of thing that we have not considered in radiobiology . 



KAMEN: I should like to bring up a point in connection with this DPN 

 experiment. I believe that when you talk about an enzyme substrate like that, to 

 talk about what happens to it away from the enzyme nnay be misleading. Have 

 there been any experiments to show that there is reduction of DPN with a DPN- 

 dependent enzynne and its substrate present? For instance, in photosynthesis, 

 despite the fact that we produce in extracts carrying out the Hill reaction, an ox- 

 idizing system with a potential near that of the oxygen electrode and simultane- 

 ously a reducing system with a potential near that of the hydrogen electrode, we 

 cannot reduce DPN or TPN directly. But if we throw in enzymes, like Ochoa's 

 "malic" enzyme together with pyruvate and CO2. then, even though we cannot 

 show any accumulation of TPNH or DPNH with H-acceptor systems, we can get 

 reduction of the pyruvate and CO2 to malate. But if you throw in enzymes like 

 alcohol dehydrogenase, then even though you cannot detect any DPN reduction, 

 you do get reduction of the fumarate to succinate. It may be then, that in the cell 

 where the DPN is bound to some characteristic enzyme, such as a dehydrogenase 

 you could be getting reduction of the DPN because there is something to pull it. 

 As long as there is nothing for it to do, it probably does not get reduced. So that 

 is the kind of thing that I think ought to get looked at more carefully. 



BARRON: I presented this experiment to demonstrate that there are ef- 

 fects produced by free radicals present in the cell. So it is not only DPN. There 

 may be other systems, too, that contribute. 



KAMEN: Most of the DPN in the cell is bound DPN. There is very 

 little free DPN in the cell. 



BARRON: I agree with you. But what I am saying is that this is an 

 experiment to demonstrate the enhancement of action. 



KAMEN: I am just saying that your model experiment may not be a 

 model experiment. 



POLLARD: I have one experiment that worries me very much, and I 

 should like to ask whether anyone here has anything analogous to it. We meas- 

 ured the ionic yield for invertase in aqueous solution and came out with a very 



