. Basic mechanisms in radiobiology. 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 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
. Basic mechanisms in radiobiology. 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 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+ H2
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