49 



BARRON: Yes, and this was so in Swallow's work. The concentration 

 of the alcohol was continuously diminished in our experimental procedure be- 

 cause of the nitrogen bubbling. We do not know how much alcohol we had in the 

 solution. I think that when we repeat the experiment we will have to determine 

 the actual amount of alcohol present. However, we could not have lost more than 

 half. So wemusthavehad 0.2 molar. I think that the concentration of alcohol 

 has to be high enough to produce a large number of radicals. If we diminish the 

 concentration of alcohol, I am afraid we will be unable to find the reduction of 

 DPN. But those are points that we have not yet worked out. 



Also, the concentration of DPN was high. We did that purposely in 

 order to demonstrate quite conclusively that there was a large formation of re- 

 duced DPN. 



CHARGAFF: What about those experiments of Joseph Weiss with high 

 dosage irradiation of nucleic acid? He used very high dosages and got fearful 

 effects. 



BARRON: The same thing happens with sulfur mustard and nitrogen 

 mustard. When large amounts are used, all kinds of effects appear. 



CHARGAFF: Is it possible that the same effects but, of course, in a 

 much lower concentration, do take place in physiological doses but cannot be de- 

 tected because the particular methods are not good enough? 



BARRON: To that question, I have no answer. We have tried very 

 hard, with the most accurate methods for the determination of phosphorus, and 

 we have never found any inorganic phosphorus. You see, Weiss irradiated with 

 1.5 million r. With amounts within 150,000 r we were unable to find any diminu- 

 tion. 



CHARGAFF: If nucleic acid has a molecular weight of six million, 

 that would mean 20, 000 nucleotides. If 1 or 2 out of these 20, 000, say, were 

 dephosphorylated, you would not see it analytically. 



BARRON: We have used adenosine triphosphate, that has a much 

 smaller molecular weight, and have observed a decrease in the absorption band 

 at 260 mfx. It was strictly proportional to the amount of radiation. But no inor- 

 ganic phosphorus was formed. 



CARTER: Scholes and Weiss have an explanation for this in terms of 

 the increase in acid lability of the phosphate, not necessarily a splitting out of 

 inorganic phosphate from the molecule. They explain the after-effect, the long 

 period of drop in viscosity that takes place subsequent to irradiation, in terms of 

 slow hydrolysis of the labile phosphate compounds. 



Also they have recently reported conversion of monoethyl phosphate to 

 acetylphosphate, which, at least, is the model for this type of reaction. 



CARTER: They say that the 4' hydroxyl group of the desoxypentose 

 moiety is extremely susceptible to attack by the perhydroxyl radical leading to 

 the production of an acid labile phosphate ester. 



BARRON: Coming back to the sulfhydryl groups, you may recall that 

 coenzyme A was oxidized in vitro with an ionic yield of 3 . It is extremely sensi- 

 tive. 



