127 



are more sensitive than proteins or any other biological structure? 



CARTER: No, there isn't, and, as a matter of fact, as Dr. Barron 

 pointed out, there is fairly good evidence to indicate that they are less sensitive. 



Inorganic phosphate can be formed from the organic phosphoryl esters, 

 and ammonia can be liberated from these solutions. All of these events take 

 place with high energy absorption. A lot of radiation is necessary to accomplish 

 this. 



Perhaps the more immediately interesting radiation effects in this area 

 are related to changes brought about in the high molecular weight desoxyribonu- 

 cleic acid by the various forms of radiation. This work probably begins with 

 that which Dr. Hollaender did with ultraviolet radiation, and then was continued 

 in cooperation with Taylor and Greenstein employing X radiation. The funda- 

 mental experiments are there. The effects are all described. They have pro- 

 vided a fertile area for re-investigation and for amplification. It was found that 

 when the polymerized desoxyribonucleic acids v/ere exposed to X radiation, they 

 rapidly lost their properties of high viscosity, and that not only this primary 

 event could be shown, but that if the irradiated nucleic acid were kept in solution 

 after irradiation, viscosity tended to decrease continuously for a long period of 

 time thereafter. 



These effects have been re-investigated by Butler and Conway and 

 Scholes and Weiss, and their investigations have brought forth several interesting 

 additional findings. In the first place, Butler and his colleague found that this 

 after-effect is largely absent when the nucleic acid is irradiated in nitrogen. 

 That is, if the nucleic acid is irradiated in the absence of air, viscosity does not 

 decrease significantly after the initial ionizing event. Scholes and Weiss, under 

 slightly different conditions, found that irradiation in nitrogen produces about 

 one-third of the after-effect of irradiation in oxygen, and this has modified to a 

 considerable extent their interpretation, but nevertheless oxygen has a profound 

 influence upon this drop in viscosity of the nucleic acid. 



KAMEN: About a week ago, there was another article in Nature by 

 Conway'") more or less taking Scholes and Weiss to task and upholding Butler's 

 and Conway's original notion. 



CARTER: That is based on a difference in techniques. Butler, after 

 irradiation, takes the nucleic acid out and dilutes it by a factor of 2. There is, 

 he says, an immediate reorientation of molecules after dilution. Whereas Scholes 

 and Weiss do their viscosity studies in the same solution, and the after-effect 

 which they get in the presence of nitrogen, Butler and Conway say is merely a 

 slow reorientation that takes place after the ionizing event. If they take the solu- 

 tion and dilute it out by a factor of 2 the event is no longer seen. 



CHARGAFF: But the original viscosity decrease during the irradiation 

 (is not influenced by absence of oxygen. 



CARTER: To a very small extent. The primary event is influenced to 

 an extremely small extent. 



PATT: Is oxygen added immediately after irradiation in all instances? 



CARTER: They have done it immediately after. 



