27 



ALLEN: To what distance of diffusion does this correspond? 



POLLARD: I cannot remember that. It is in the paper that Smith (3) 

 worked out. 



ALLEN: This seems awfully short for the lifetime of a radical in pure 

 water. Could it be possible that the catalase, when it is in the monolayer stage, 

 is less radiosensitive than it is when dispersed molecularly in water? 



POLLARD: I think if you assume that the catalase has an unequal sen- 

 sitivity, the lifetime does not become any shorter. 



ALLEN: Is there some basis for an estimate of the probability of 

 collision of the radical with a monolayer and of its doing anything? 



POLLARD: Well, that was what worried Smith. He measured the 

 ionic yield for the catalase and got 20 ion pairs to inactivate 1 catalase molecule. 

 I think he assumed that this corresponded to a high sensitivity region on the sur- 

 face, which was l/20th of the whole surface, and he used that l/ZOth of the sur- 

 face as the region on which the radical would have to go. Otherwise, he would 

 come out with a figure like Lea's, which he didn't believe. He has a check 

 against this in the bovine serum albumin where again you get a figure of the same 

 order. I do know that he does not treat the whole molecule as the sensitive re- 

 gion. I know that it is a fraction and it is a fraction determined by the measured 

 ionic yield. Of course, if a multiple number of ions is needed to arrive even to 

 a sensitive place, then it would be different. 



ALLEN: Is it not still possible that the whole structure of the catalase, 

 and particularly its hydration structure, may be changed when it goes into this 

 monolayer? 



way. 



POLLARD: It seems to work on hydrogen peroxide in nearly the same 



MAZIA: But the solubility certainly has changed. 



POLLARD: It is just the enzymatic activity that apparently hasn't 

 changed appreciably. 



