130 



cule. 



Scholes and Weiss' ' contend that ionizing radiation attacks the pentose 

 moiety, or in the case of the desoxynucleic acid, the desoxypentose moiety. 



They argue from analogy of the irradiation of the low molecular weight 

 organic phosphoryl esters. Ethyl phosphate irradiated with about 9 x 10'* r can 

 be transformed into acetylphosphate. 



Glycerophosphate irradiated at about the same level also undergoes an 

 oxidative type reaction, which they formulate as an attack by the perhydroxyl 

 radical which converts the secondary hydroxyl to a ketone. The net effect of 

 converting the hydroxyl to a ketone is to labilize the phosphate. 



They argue that the same sequence of events will take place in the de- 

 soxypentose moiety. That the attack of the oxidative radical will be on the 

 lactone, with a rupture of the furanose ring and with a labilization of adjacent 

 phosphate. Consequently the chain will rupture, and the high molecular weight 

 characteristics of the molecule will disappear. 



Most people argue against this interpretation because of the inability 

 to find traces of inorganic phosphate or other degraded components and the fact 

 that changes in viscosity can take place without finding these components. 



Concomitant changes in molecular weight have been studied by other 

 criteria. While viscosity changes may be extensive, fundamental di-ester link- 

 ages have been unaffected and sedimentation behavior may be unchanged. What 

 has been affected is the high molecular weight orientation that is based upon 

 association or aggregation or weak bonding of some nature that cannot be identi- 

 fied with fundamental particle size. (5) 



However, Scholes and Weiss ^ ' find that if they take a nucleic acid 

 and do a very mild acid degradation, they get virtually no phosphate. From the 

 irradiated nucleic acid they get 15 times the amount of inorganic phosphate. 



CHARGAFF: I have had the feeling that there is something wrong 

 with these experiments. 



PLATZMAN: Why would they be so hard to repeat? 



BARRON: We have attempted to repeat them. We have never found 

 phosphoric acid or ammonia. 



CARTER: Have you ever tried the acid labile phosphate experiment? 



BARRON: No. We irradiated nucleic acid with 50,000 r, and we 

 could not find either ammonia or phosphate. 



CARTER: But nevertheless we have to keep these experiments of 

 Butler in mind, that something has taken place on the nucleic acid molecule 

 which makes it more susceptible to attack by peroxide and the oxidizing radi- 

 cals, and somehow or other we have to come up with an explanation, not to 

 satisfy us or to make us happy but so we can do experiments. 



ALLEN: Do I understand that the acid labile phosphate is increased by 

 radiation? 



