44 



reasonable figure of about .016, or something like that, for the ionic yield. 

 Then we just took some yeast cells and put them in distilled water and irradi- 

 ated them, extracting the invertase afterward, and we measured how much we 

 had lost. We didn't lose any. Even when yeast cells in distilled water were ir- 

 radiated with 200, 000 r there was no observed effect on the invertase, whereas 

 1000 r given to the commercial preparation in distilled water led to a definite 

 effect. 



KAMEN: Isn't that the same as Forssberg's work on catalase where 

 he found that irradiating the liver gave no inactivation of catalase whereas in 

 vitro the free stuff was inactivated readily *? 



POLLARD: I find myself, therefore, a little bewildered at taking 

 over experiments that are designed to be true in aqueous solution to actual bio- 

 logical systems because, after all, normal yeast is in its right environment. 



COHN: Did you ever set up a row of tubes with 10 units of invertase, 

 20 units, 40 units, and on up to 100 units of invertase and then give all of them 

 a fixed amount of radiation? 



POLLARD: Oh yes. 



COHN: What happens to them ^ 



POLLARD: If you do this in aqueous solution, when enough invertase 

 is present, you get the same amount inactivated per roentgen. If you have too 

 little invertase, the radical is gone before it can be effective. 



COHN: Suppose you have just enough radiation to give 100 percent 

 inhibition in the tube with 50 units of invertase and then you give that amount of 

 radiation to all of them? 



POLLARD: You won't get just 50 units inactivated all the way along. 

 It won't work quite that way. 



COHN: But you might get 10 percent inhibition in the tube that had 

 100 units. 



POLLARD: Yes. The number of units of invertase we measured in 

 theyeastcells, I think, was well within the range of our in vitro experiments. 



COHN: Of course, yeast has a lot of other things besides invertase. 



POLLARD: That is right. That, I think, is perhaps the thing I 

 thought of. I believe that the interaction of the other things present is para- 

 mount in interpretation. 



JONES: I should like to ask Dr. Barron whether the idea originally 

 put forward by Dale of simple protection by ionization product capture still 

 holds. 



BARRON: Yes, that is very well shown by irradiation of protein. 

 An exposure of 75,000 r will precipitate protein irradiated in water solution. 

 If you irradiate the same protein with sodium chloride present, there is no pre- 

 cipitation. Of course, one might say that the protein has combined with the 

 chloride to form a more stable protein. So this possibility must also be con- 



