33 



distribution of the -SH groups will hinder 

 oxidation. In Table II, we have the -SH 

 enzymes, D-amino acid oxidase and hex- 

 okinase, which are more resistant to X 

 irradiation. 



MAGEE: How did you calculate 

 the ionic yield? 



BARRON: In these experiments 

 ionic yields were calculated by assuming 

 that 1.61 x 10^^ ion pairs are formed per 

 g. of water per r unit. 



PLATZMAN: Thirty-five volts 



per ion pair? 



BARRON: 



32. 5 volts. 



X lo 



I want to discuss now the problem 

 of induced oxidation-reduction reactions 

 by the free-radicals produced during ox- 

 idation with OH and O2H radicals. I 

 would like to call this process enhance- 

 ment of irradiation. These radicals, 

 having a longer half-life than the OH and 

 O^H radicals, may diffuse longer dis- 

 tances. This, in my opinion, is of tre- 

 mendous importance to the biologist be- 

 cause it may explain effects produced by 

 small doses of ionizing radiations, and 

 effects observed at long distances from 

 the ionizing tracks. While reduced pyri- 

 dine nucleotide (DPNH) is oxidized by X 

 irradiation, the oxidized form (DPN"*") is 

 not reduced (4). In the same manner, 

 ethanol is oxidized to acetaldehyde, 'and lactate to pyruvate, while the reverse 

 process does not occur. Swallow (5) found that when aqueous solutions -- nitro- 

 gen saturated -- of DPN+ and ethanol were X irradiated, there was formation of 

 DPNH as shown by spectrophotometric measurements. Swallow did not measure 

 enzymatic activity of the irradiation product. We have confirmed Swallow's ex- 

 periments. Moreover, the same reduction, although to a lesser degree, was 

 found after irradiation of lactate plus DPN+ (Figure 1), and also after irradia- 

 tion of isoproply alcohol plus DPN+. We have, in this case, the following reac- 

 tions taking place with ethanol and DPN"^: 



Figure 1. Effect of X-irradiation on the 

 absorption spectrum of cytidine and cy- 

 tosine X-ray dose, 20,000 r. 



CH3CH2OH+ OH 



CH3CHOH + DPN 

 CH3CH2OH+ OH 

 CH^CHOH + DPNH 



^ CH3CHOH+ H2O 



DPNH+ CH3COH 



■> CH3CHOH + H2O 



CH3COH+ DPNH +H + 



(1) 

 (2) 

 (3) 



(4) 



The OH radical oxidizes ethanol to the half-oxidized radical, CH3CHOH, 

 which in turn reduces DPN to the half-reduced radical DPNH. A second molecule 

 of alcohol radical completes the reduction of DPN. The reduction is thus pro- 



