274 Discussion 



Pirie: Does your weakening effect increase with time after radiation 

 or can you stop it, i.e. if you irradiate your whole cell and immediately 

 take out the nuclei, are they then stable? 



Alexander: There is certainly a time effect with whole cells but for 

 technical reasons it is very difficult to reduce the time interval to less 

 than about five minutes. 



Holmes: Do we know any useful DNAse inhibitors? You could not 

 apply them after irradiation, they would not act quickly enough. 

 Could they be used as protective substances ? In the case of a proteolytic 

 enzyme, for instance, we might imagine that cystine and cysteine would 

 interfere with it. 



Alexander: This is an idea to which Prof. Bacq and I have given much 

 thought. We don't think that DNAse is the only enzyme concerned 

 and it is possible that there are some other enzymes which are capable 

 of de-geling the nucleoprotein in other ways. 



Spiegelman : Has the effect of citrate been tried on this ? 



Alexander: Yes, but citrate does not protect. 



Gray: Where is the DNAse situated in the cells? 



Bracket: It is mostly cytoplasmic. 



Alexander: Is there evidence for any DNAse in the nucleus? 



Bracket: There is always the possibility that some of the DNAse is 

 sticking to the nuclei. One finds a little DNAse in them, but it is dif- 

 ficult to say, when an enzyme is present only in small amounts in a given 

 cellular fraction, that it has not been adsorbed during the isolation pro- 

 cesses. 



Hollaender: We would like very much to have a physical anti-ioniza- 

 tion agent. Hypertonic salt solution is probably something of a physical 

 agent; putting a new balance of ions in where this balance has been 

 upset. But if one could visualize an agent which would counteract the 

 ions, hold them in some form immediately following radiation, I think 

 the problem would be very much simpler. 



Swanson: There is one possibility in the infrared. Some work has 

 been published recently by Moh and Withrow (1955, Plant Physiol., 

 abstracts), where the 6200 A region is believed to be inhibitory in 

 terms of chromosome breaks, while the 7100-8200 A region adds to the 

 X-ray damage. These correspond to the regions of the spectrum that 

 were worked on by Hendricks in his seed germination studies, with the 

 shorter wavelengths being inhibitory, the longer ones capable of break- 

 ing dormancy. 



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